March 2013Electronics Project Circuts

5 channel radio remote control

Sunil Jadhavar 5:27 AM

<b>TX-2B / RX / 2B  5 channel radio remote control.</b><br />

<div style="text-align: justify;">
This article is about a simple 5 channel
 radio remote control circuit based on ICs TX-2B and RX-2B from Silan 
Semiconductors.  TX-2B / RX-2B is a remote encoder decoder pair that can
 be used for remote control applications. TX-2B / RX-2B has five 
channels, wide operating voltage range (from 1.5V to 5V), low stand by 
current (around 10uA), low operating current (2mA), auto power off  
function and requires few external components. The TX-2B / RX-2B was 
originally designed for remote toy car applications, but they can be 
used for any kind of remote switching application.</div>
<br />
<b><span style="font-size: large;">Circuit diagrams and description</span>.</b><br />

<h4>
Remote encoder / transmitter circuit.</h4>
<div class="wp-caption aligncenter" id="attachment_6287" style="width: 1185px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/07/5-channel-radio-remote-control-circuit.jpg"><img alt="radio remote control transmitter ciruit" class="size-full wp-image-6287" height="250" src="http://www.circuitstoday.com/wp-content/uploads/2011/07/5-channel-radio-remote-control-circuit.jpg" title="5 channel radio remote control circuit" width="640" /></a><div class="wp-caption-text">
5 channel redio remote control encoder / transmitter circuit</div>
</div>
<div style="text-align: justify;">
The TX-2B forms the main part of the 
circuit. Push button switches S1 to S5 are used for activating (ON/OFF) 
the corresponding O/P channels in the receiver / decoder circuit. These 
push button switches are interfaced to the built-in latch circuitry of 
the TX-2B. Resistor R7 sets the frequency of the TX-2B’s internal 
oscillator. Resistor R1 and Zener diode D1 forms a simple Zener 
regulator circuit for providing the IC with 3V from the 9V main supply. 
C2 is the filter capacitor while C1 is a noise by-pass capacitor. D2 is 
the power on indicator LED while R6 limits the current through the same 
LED. S1 is the ON/OFF switch. The encoded control signal will be 
available at pin 8 of the IC. The encoded signal available at pin 8 is 
without carrier frequency. This signal is fed to the next stage of the 
circuit which is a radio transmitter. Crystal X1 sets the oscillator 
frequency of the transmitter section. R2 is the biasing resistor for Q1 
while R3 limits the collector current of Q1. The encoded signal is 
coupled to the collector of Q1 through C3 for modulation. Transistor Q2 
and associated components provide further amplification to the modulated
 signal.</div>
<h4 style="text-align: justify;">
Remote receiver / decoder circuit.</h4>
<h4 style="text-align: justify;">
<div class="wp-caption aligncenter" id="attachment_6288" style="width: 910px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/07/5-channel-remote-control-receiver.png"><img alt="" class="size-full wp-image-6288" height="457" src="http://www.circuitstoday.com/wp-content/uploads/2011/07/5-channel-remote-control-receiver.png" title="5 channel remote control receiver" width="640" /></a><div class="wp-caption-text">
5 channel radio remote decoder</div>
</div>
</h4>
<div style="text-align: justify;">
The remote receiver circuit is built 
around the IC RX-2B. The first part of the circuit is a radio receiver 
built around transistor Q1. The received signal is demodulated and fed 
to pin 14 of the IC. Pin 14 is the input of the built in inverter inside
 the IC. R2 sets the frequency of the IC’s internal oscillator. O/P 1 to
 O/5 are the output pins that are activated corresponding to the push 
buttons S1 to S5. Zener diode D1 and resistor R12 forms an elementary 
Zener regulator for supplying the RX-2B with 3V from the 9V main supply.
 C12 is the filter capacitor while R11 is the current limiter for the 
radio receiver section. Diode D2 protects the circuit from accidental 
polarity reversals. C15 is another filter capacitor and C14 is a noise 
by-pass capacitor.</div>
<h3>
Notes.</h3>
<ul>
<li>This circuit can be assembled on a vero board or  a PCB.</li>
<li>Use 9V DC for powering the transmitter / receiver circuits.</li>
<li>Battery is the better option for powering the transmitter / receiver circuit.</li>
<li>If you are using a DC power supply circuit, it must be well regulated and free from any sort of noise.</li>
<li>Both ICs must be mounted on holders.</li>
</ul>
<h4>
Interfacing relay to the RX-2B output.</h4>
<div style="text-align: justify;">
The method for interfacing a relay to 
the output of RX-2B is shown below. When push button switch S1 of the 
transmitter circuit is pressed, pin O/P1 (pin 7 of the RX-2B) goes high.
 This makes the transistor 2N2222 to conduct and the relay is activated.
 The same technique can be applied to other output pins of the RX-2B. 
The relay used here is a 200 ohm type and at 9V supply voltage the load 
current will be 45mA which is fine for 2N2222 whose maximum possible 
collector current is 900mA. When using relays of other ratings this 
point has to be remembered and do not use a relay that consumes a 
current more than the maximum possible collector current of the driver 
transistor.</div>
<div style="text-align: justify;">
</div>
<div class="wp-caption aligncenter" id="attachment_6286" style="width: 422px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/07/interfacing-relay-to-RX-2B-output.png"><img alt="transistor relay driver" class="size-full wp-image-6286" height="363" src="http://www.circuitstoday.com/wp-content/uploads/2011/07/interfacing-relay-to-RX-2B-output.png" title="interfacing relay to RX-2B output" width="412" /></a><div class="wp-caption-text">
Interfacing relay to the remote decoder</div>
</div>
<table><tbody>
<tr><td>

5 channel radio remote control

TX-2B / RX / 2B 5 channel radio remote control. This article is about a simple 5 channel radio remote control circuit based on ICs TX-2...

Flashing battery monitor

Sunil Jadhavar LED Projects 5:24 AM

<div style="text-align: justify;">
<b>Description.</b></div>
<div style="text-align: justify;">
Here is a simple circuit in which an LED
 will continue flashing as long as the voltage of the battery to be 
monitored is above the set level.The transistors Q1 and Q2 are wired as a
 complementary astable multivibrator.The circuit can operate from  a 
voltage range from 6V to 12V. The voltage level at which LED has to stop
 flashing can be set by adjusting the preset R4.When the battery voltage
 reaches the threshold the flashing frequency decreases and when the 
voltage goes below the threshold the LED becomes OFF.The diode D1 is 
used to compensate the changes in the base emitter voltage of Q1 due to 
temperature changes.</div>
<div style="text-align: justify;">
<b>Circuit diagram with Parts list.</b></div>
<div style="text-align: justify;">
<b><a href="http://www.circuitstoday.com/wp-content/uploads/2009/04/flashing-battery-monitor-circuit.jpg"><img alt="flashing-battery-monitor-circuit" class="alignnone size-full wp-image-846" height="450" src="http://www.circuitstoday.com/wp-content/uploads/2009/04/flashing-battery-monitor-circuit.jpg" title="flashing-battery-monitor-circuit" width="614" /></a><br />
</b></div>
<div style="text-align: justify;">
<b>Notes.</b></div>
<ul>
<li>Assemble the circuit on a general purpose PCB.</li>
<li>Batteries from 6V to 12V can be monitored by this circuit.</li>
<li>The diode D1 must be a Schottky diode.</li>
</ul>

Flashing battery monitor

Description. Here is a simple circuit in which an LED will continue flashing as long as the voltage of the battery to be monitored is a...

Battery charger circuit using L200

Sunil Jadhavar 5:19 AM

<strong>Description.</strong>
<br />
<div align="justify">
A very simple battery charger circuit having reverse 
polarity indication is shown here.The circuit is based on IC L200 . L200
 is a five pin variable voltage voltage regulator IC.The charging 
circuit can be fed by the DC voltage from a bridge rectifier or center 
tapped rectifier.Here the IC L200 keeps the charging voltage 
constant.The charging current is controlled by the parallel combination 
of the resistors R2 & R3.The POT P1 can be used to adjust the 
charging current.This circuit is designed to charge a 12 V lead acid 
battery.The transistor t1,diode D3 and LED are used to make a battery 
reverse indicator.In case the battery is connected in reverse polarity 
,the reverse polarity indicator red LED D5 glows.When the charging 
process is going on the battery charging indicator green LED D4 glows.</div>
<div align="justify">
<br /></div>
<div align="justify">
<br /></div>
<div align="justify">
<strong>Circuit diagram with Parts list.</strong></div>
<div align="justify">
<br /></div>
<div align="justify">
 <a href="http://www.circuitstoday.com/wp-content/uploads/2008/08/battery-charger-circuit-using-l200.JPG" title="battery-charger-circuit-using-l200.JPG"><img alt="battery-charger-circuit-using-l200.JPG" src="http://www.circuitstoday.com/wp-content/uploads/2008/08/battery-charger-circuit-using-l200.JPG" /></a></div>
<div align="justify">
<br /></div>
<div align="justify">
<br /></div>
<div align="justify">
<strong>Notes. </strong></div>
<ul>
<li>The circuit can be assembled on a good quality PCB or common board.</li>
</ul>
<ul>
<li>The values of R2 & R3 can be obtained from the equation,</li>
</ul>
(<strong>R</strong>2//<strong>R</strong>3) =( <strong>V</strong>5-<strong>2</strong>)/(<strong>I</strong>o).<br />

Where <strong>V</strong>5 is  the charging voltage (voltage at pin 5) and <strong>I</strong>o is the charging current.<br />

<ul>
<li>The POT R8 can be used for fine adjustments of charging current.</li>
</ul>
<ul>
<li>If battery is connected in reverse polarity the RED LED will glow.</li>
</ul>
<ul>
<li>When the  charging is going on the GREEN LED will glow.</li>
</ul>
<ul>
<li>The rectified input voltage to the charger can be 18V.</li>
</ul>

Battery charger circuit using L200

Description. A very simple battery charger circuit having reverse polarity indication is shown here.The circuit is based on IC L200 . L2...

Three phase auto changer circuit

Sunil Jadhavar 5:18 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
The circuit given here is designed by Mr.Seetharaman V.S (<a href="mailto:seethasub@hotmail.com">seethasub@hotmail.com</a>) from Chennai.</div>
<div style="text-align: justify;">
<span style="color: grey;"><em><strong>Seetharaman’s comments about the circuit</strong></em></span>: This circuit is a modification of  High & Low voltage cut-off with delay& alarm
 circuit  appeared in Circuits today, which I have tried and found to be
 quite reliable. You can adopt this circuit with small modification. Use
 a transformer with secondary 15 – 0 – 15 AC Volt at 500mA, for 18Volt 
relay operation. Normally any modern electrical / electronic equipment 
can operate with 230 Volt ± 15% AC supply. That is, it can stand normal 
voltage operating range of 195 to 265 Volts. It may misbehave beyond 
this voltage range. You can choose the practical voltage required for 
the low end high cut off to change over to other phase.</div>
<strong>Circuit diagram.</strong><br />

<strong>Connection diagram.</strong><br />

<strong>Notes.</strong><br />

<ul>
<li> Set VR3 for minimum voltage to switch on the relay (Say 195 Volt input).</li>
<li>Set VR1 to switch off the relay above a particular voltage (say 260Volt input).</li>
<li>You can use a 100μF 40 Volts good make in parallel with relay for chatter free operation.</li>
<li>Each Phase you have to use one module as above.</li>
<li>The relay interconnections are shown in the connection diagram above.</li>
<li>T1 can be a 15-015 V secondary, 230V primary, 500mA step down transformer.</li>
</ul>

Three phase auto changer circuit

Description. The circuit given here is designed by Mr.Seetharaman V.S ( seethasub@hotmail.com ) from Chennai. Seetharaman’s comments ab...

LDO regulator / low dropout regulator

Sunil Jadhavar 5:16 AM

<div style="text-align: justify;">
LDO regulator means low dropout 
regulator. An LDO voltage regulator is just a DC linear voltage 
regulator which can be operated with a very small input-output voltage 
differential. This input output voltage differential is called dropout 
voltage. In simple words dropout voltage is the voltage dropped by the 
regulator circuitry alone for its working. For example, an LM2941 LDO 
voltage regulator has a dropout voltage of only around 0.5V, which means
 that in order to get 5 volts at the output you need to input only 5.5 
volts where an ordinary 7805 linear voltage regulator has a dropout 
voltage of around 2V. This means that, in order to get 5V at the output 
of 7805 you need to input at least 7V.</div>
<h3 style="text-align: justify;">
LDO regulator working.</h3>
<div class="wp-caption aligncenter" id="attachment_6066" style="width: 613px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/LDO-regulator-schematic.png"><img alt="LDO regulator block diagram" class="size-full wp-image-6066" height="414" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/LDO-regulator-schematic.png" title="LDO regulator schematic" width="603" /></a><div class="wp-caption-text">
Schematic of a LDO regulator</div>
</div>
The image shown above is the schematic of a typical LDO voltage 
regulator. The working principle of LDO regulator is just like that of 
an ordinary linear voltage regulator. The essential components of an LDO
 voltage regulator are a reference voltage source, error amplifier and 
series pass element (BJT or MOSFET). The voltage drop across the series 
pass element is controlled by the error amplifiers output in order to 
control the output voltage. For example, suppose the load current 
decreases and as results the output voltage tends increase. This 
increase in output voltage will increase the error voltage (VERR).The 
output of the error amplifier will increase, making the series pass 
element ( P-Channel MOSFET) less conducting, which results in the 
reduction of the output voltage and the output voltage is brought back 
to the original level.<br />

<div style="text-align: justify;">
As I said above the working of a LDO 
voltage regulator is similar to the working of an ordinary linear 
voltage regulator and the only difference is in the schematic topology 
of their internal circuitry. Ordinary linear regulators (7805, LM117, 
LM317 etc) uses a common collector scheme while the LDO regulators use 
an open collector (termed as open drain if a MOSFET is used as the 
series pass element) scheme.</div>
<h4 style="text-align: justify;">
Common collector scheme.</h4>
<div style="text-align: justify;">
Common collector scheme is one of the 
three basic transistor configurations. Here base is the input terminal, 
emitter is the output, and supply voltage is applied to the collector 
terminal. The series pass transistor inside an ordinary linear voltage 
regulator is wired in this configuration. Fig A shows the common 
collector scheme (also termed as emitter follower scheme).</div>
<div style="text-align: justify;">
</div>
<div class="wp-caption aligncenter" id="attachment_6067" style="width: 674px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/common-collector-and-open-collector-scheme.png"><img alt="emitter follower scheme and open drain scheme" class="size-full wp-image-6067" height="355" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/common-collector-and-open-collector-scheme.png" title="common collector and open collector scheme" width="664" /></a><div class="wp-caption-text">
Common collector and open collector scheme</div>
</div>
<h4 style="text-align: justify;">
Open collector scheme.</h4>
<div style="text-align: justify;">
Many integrated circuits like LDO 
voltage regulators this scheme for wiring the series pass element (BJT 
or MOSFET). The input signal (which comes from the previous stage inside
 the IC) is coupled to the base of the BJT (or gate of the MOSFET), 
collector is left open and it is connected to a pin of the IC while the 
emitter is connected to the IC ground. This configuration makes it easy 
to saturate the series pass element and hence the dropout voltage is 
minimized.Fig B shows the open collector / drain scheme.</div>
<h3 style="text-align: justify;">
Practical LDO regulator circuit.</h3>
<h3 style="text-align: justify;">
<div class="wp-caption aligncenter" id="attachment_6068" style="width: 641px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/LDO-regulator-using-LM2941.png"><img alt="practical LDO regulator circuit" class="size-full wp-image-6068" height="434" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/LDO-regulator-using-LM2941.png" title="LDO regulator using LM2941" width="631" /></a><div class="wp-caption-text">
LDO regulator using LM2941</div>
</div>
</h3>
<div style="text-align: justify;">
The circuit shown above is of a 
practical LDO regulator circuit using IC LM2941 from National 
semiconductors. LM2941 is an integrated LDO voltage regulator IC whose 
output can be adjusted. The IC has many good features like thermal 
shutdown, transient protection, short circuit protection etc. The 
reverse polarity protection feature makes this IC very applicable in 
automotive applications. The output voltage can be adjusted from 5V to 
20V and the dropout voltage is 0.5V at 1A output current.<br />
In the circuit the voltage divider network comprising of R1 and R2 sets 
the output voltage. Capacitor C2 is the input filter which is very 
essential if the regulator circuitry is situated away from the 
rectifier+filter module. Capacitor C1 is the output filter while S1 is 
the ON/OFF switch. Resistor R3 is used to ensure the necessary 300mA 
pull up current which is necessary for proper shutdown when the switch 
S1 is made open.</div>
<h3 style="text-align: justify;">
Notes.</h3>
<ul>
<li>The circuit must be assembled on a good quality PCB.</li>
<li>A heat sink is required for application above few hundred milli amps.</li>
<li>Vout = 1.275 ((R1 + R2)/R1)</li>
<li>During calculation select R1=1K and solve for R2.</li>
<li>Selecting R1 = 1K will make the input bias current error of the adj pin negligible.</li>
<li>Reducing the value of C1 below 22uF will induce instabilities and 
also this capacitor must be placed as close as possible to the IC on the
 PCB.</li>
</ul>
<table><tbody>
<tr><td>

LDO regulator / low dropout regulator

LDO regulator means low dropout regulator. An LDO voltage regulator is just a DC linear voltage regulator which can be operated with a ve...

Regulated DC power supply

Sunil Jadhavar 5:14 AM

<b>Regulated DC Power Supply using transistors.</b><br />
<br />

<div style="text-align: justify;">
A low ripple regulated DC power supply 
designed based on transistors is shown here. Such transistor voltage 
regulators are suitable for application where high output current is 
required. Conventional integrated series regulators like 7805 can only 
deliver up to 1A. Additional series pass transistors have to be added to
 the 7805 based regulator circuit for improving their current capacity.</div>
<h3>
Description.</h3>
<div style="text-align: justify;">
The circuit shown below is a basic 
series voltage regulator based on transistors. Transistor Q1 (2N 3054) 
and Q2 (2N 3055) form a darlington pair. Resistor R1 provides the base 
current for Q1 and also keeps the zener diode D2 in the active region. 
The overall working of the circuit can be demonstrated by explaining two
 situations.</div>
<ul>
<li style="text-align: justify;">When the input voltage (output of the 
rectifier section) increases, the output voltage of the regulator (Vout)
 also increases. This increase in Vout decreases the base emitter 
voltage of Q2 because the zener diode D2 is operating in the breakdown 
region and the voltage across it is unchangeable. This decrease in V<sub>BE</sub> increases the collector emitter resistance  of Q2 and so the output voltage (Vout) gets reduced accordingly.</li>
<li style="text-align: justify;">When the output load increases, the output voltage (Vout) gets reduced. This decrease of output voltage (Vout) makes V<sub>BE</sub> of Q2 to decrease. This reduces the collector emitter resistance of Q2 and so the output voltage gets increased accordingly.</li>
</ul>
<h3>
Circuit diagram.
<div class="wp-caption aligncenter" id="attachment_6483" style="width: 849px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/10/regulated-dc-power-supply.png"><img alt="zener regulated dc power supply" class="size-full wp-image-6483" height="327" src="http://www.circuitstoday.com/wp-content/uploads/2011/10/regulated-dc-power-supply.png" title="regulated dc power supply" width="640" /></a><div class="wp-caption-text">
Regulated dc power supply</div>
</div>
</h3>
<h3>
Notes.</h3>
<ul>
<li>If 5A bridge is not available, then make one using 6A6 diodes.</li>
<li>Transistor Q2 requires a heat sink.</li>
<li>An optional 5A fuse can be added in series to the output.</li>
<li>Breakdown voltage of the zener diode D2 must be chosen according to 
the output voltage you need,         and it is according to the 
equation, Vout = Vz – 0.7.</li>
</ul>
<table><tbody>
<tr><td>

Regulated DC power supply

Regulated DC Power Supply using transistors. A low ripple regulated DC power supply designed based on transistors is shown here. Such t...

Transformerless switch mode power supply circuit

Sunil Jadhavar 5:13 AM

<span style="font-size: small;"><b>12V/120mA switch mode power supply circuit.</b></span><br />
<br />

Transformer less switch mode power supplies have become very popular 
these days. The circuit shown below is of a 12V/120mA output, 85 to 230V
 AC input transformerless switch mode power supply using LNK304 IC. 
Applications of a power supply based on this IC includes hand held 
devices, timers, small appliances, LED drivers, industrial gadgets etc.<br />

<div style="text-align: justify;">
LNK304 is a low component count, 
efficient off-line switcher IC that can support buck, buck-boost and 
flyback topologies. The IC has a built in auto start circuit for short 
circuit and open loop fault protection. Other features of LNK304 
includes low temperature variation, thermal shut down,high break down 
voltage, good line & load regulation, high band width , wide input 
voltage range (85 to 230V AC) etc. In general the LNK304 has a better 
performance when compared to the many other discrete buck regulators.</div>
<div style="text-align: justify;">
<br /></div>
<div class="wp-caption aligncenter" id="attachment_6115" style="width: 642px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/LNK304-pin-configuration-typical-application.png"><img alt="" class="size-full wp-image-6115" height="294" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/LNK304-pin-configuration-typical-application.png" title="LNK304 pin configuration & typical application" width="632" /></a><div class="wp-caption-text">
LNK304 pin configuration and typical application</div>
</div>
<div style="text-align: justify;">
The pin configuration and the typical 
application diagram of LNK304 are shown above. Drain (D) pin the drain 
connection of the built in power MOSFET. The external by pass capacitor 
(0.1uF) is connected to the BYPASS (BP) terminal. FEEDBACK (FB) pin 
controls the switching of the built in power MOSFET. A current above 
than 49uA delivered to this pin will inhibit the switching. The internal
 power MOSFETs source is connected to the SOURCE (S) pin.</div>
<h3 style="text-align: justify;">
LNK304 based switch mode power supply circuit.</h3>
<div class="wp-caption aligncenter" id="attachment_6116" style="width: 972px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/06/12V-transformerless-switching-power-supply.png"><img alt="12V switch mode power supply" class="size-full wp-image-6116" height="349" src="http://www.circuitstoday.com/wp-content/uploads/2011/06/12V-transformerless-switching-power-supply.png" title="12V transformerless switch mode power supply" width="962" /></a><div class="wp-caption-text">
12V /120 switch mode power supply circuit</div>
</div>
<div style="text-align: justify;">
The circuit diagram of a practical 
12V/120mA transformerless switch mode power supply is shown above. 
Resistor R1, capacitors C1 and C2, diodes D1 and D2 and inductor L1 
forms the input stage. D1 and D2 forms the rectifier section while C1 
and C2 are input filters. Resistor R1 which is a fusible resistor limits
 the inrush current, increases differential mode noise attenuation and 
also serves as an input safety fuse.</div>
<div style="text-align: justify;">
The next stage is the regulator stage 
which consists of IC LNK304, diodes D3 and D4, capacitors C3, C4 and C5,
 resistors R3, R4 and R5 and inductor L2. D3 is the freewheeling diode 
while L2 is the output choke. C5 is the output filter capacitor which 
limits the output ripple voltage to a value as low as possible. The IC 
LNK304 is so configured that the power supply operated in the most 
discontinuous mode and that’s why a fast recovery diode (UF4005) is used
 as the freewheeling diode (D3). UF4005 has a reverse recovery time of 
around 75nS and it is well enough for the given situation.</div>
<div style="text-align: justify;">
The voltage drop across diodes D3 and D4
 are practically same and so the voltage across C4 tracks the output 
voltage and this voltage is picked by the network comprising of 
resistors R2, R3 and is fed to the feedback pin. R2 and R3 sets the 
output voltage and for 12V output the voltage at the feedback pin must 
be 1.65V DC. The circuit attains regulation by skipping the switching 
cycles. When the output voltage rise, the current at the feedback pin 
also rises and when the current rises above the threshold value, 
subsequent cycles are skipped until the current at the feedback pin goes
 below the threshold and thus a constant output voltage is maintained.</div>
<div style="text-align: justify;">
The IC will auto restart if no cycles 
are skipped during a 50mS time period and this limits the maximum output
 power to 6% of the maximum over load power. That’s how over load 
protection is attained. Resistor R4 serves as a small preload which 
nullifies the effects of tracking error.</div>
<h3>
Notes.</h3>
<ul>
<li>Assemble the circuit on a good quality PCB.</li>
<li>LNK304 is a very high efficiency switching regulator IC that has a hand full of applications.</li>
<li>LNK304 is commonly available in SMD package (DIP is also available) and care must be taken while soldering it.</li>
<li>D1 and D2 are standard 1N4007 silicon rectifier diodes.</li>
<li>D3 (UF4005) is a fast recovery diode.</li>
<li>D4 (1N4005GP) is a glass passivated diode.</li>
<li>C3 can be a ceramic capacitor.</li>
<li>C1,C2 and C4 are polyester capacitors.</li>
<li>C5 can be electrolytic or polyester capacitor.</li>
<li>Voltage ratings of the capacitors are shown in the circuit diagram.</li>
<li>R1 is a fusible, fire proof resistor.</li>
<li>Maximum possible output current is 120mA.</li>
<li>Input voltage range is 85 to 230V AC.</li>
</ul>

Transformerless switch mode power supply circuit

12V/120mA switch mode power supply circuit. Transformer less switch mode power supplies have become very popular these days. The circuit...

10A Adjustable voltage Regulator MSK 5012

Sunil Jadhavar 5:11 AM

<div style="text-align: justify;">
MSK5012 is a highly reliable adjustable 
voltage regulator.Whose output can be programmed using two resistors. 
The regulator has a very low dropout voltage(0.45v @10A  )due to the 
usage of MOSFET with very low Rds (ON) as the internal series pass 
element.The MS5012 has a high level of accuracy and ripple rejection is 
around 45dB. It is available in a 5 pin Sip package that is electrically
 isolated from the internal circuitry. This give us the freedom to fit 
the IC directly to the heat sink and this sort of direct heat sinking 
improves the thermal dissipation.</div>
<h3>
<strong>Description.</strong></h3>
<div style="text-align: justify;">
The output voltage of this circuit is adjustable from 1.3v to 36v DC.Resistors R<sub>1</sub> and R<sub>2</sub> are used for programming the output voltage.For all applications, value of R<sub>2</sub> is fixed to 10K. The relationship between R<sub>1</sub>,R<sub>2</sub> and output voltage Vout is according to the equation R<sub>1</sub>=R<sub>2</sub>(Vout/1.235)-1. C<sub>1</sub>
 is a filter capacitor which is also a part of the gate drive circuit of
 the internal series pass MOSFET. Around three times the input voltage 
will appear across this capacitor and so the its voltage rating must be 
selected accordingly.C<sub>2</sub> is the input filter capacitor while C<sub>3</sub> is the output filter capacitor.</div>
<h3 style="text-align: justify;">
Circuit  diagram.</h3>
<div class="wp-caption aligncenter" id="attachment_6496" style="width: 607px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/10/10A-adjustable-voltage-regulator-MSK5012.png"><img alt="adjustable regulator" class="size-full wp-image-6496" height="329" src="http://www.circuitstoday.com/wp-content/uploads/2011/10/10A-adjustable-voltage-regulator-MSK5012.png" title="10A adjustable voltage regulator MSK5012" width="597" /></a><div class="wp-caption-text">
10A adjustable voltage regulator MSK5012</div>
</div>
<h3>
<strong>Notes.</strong></h3>
<ul>
<li>Input voltage 3v to 36v DC.</li>
<li>Output voltage range 13v to 36v DC.</li>
<li>Typical application of MSK5012 are high efficiency linear 
regulators, constant voltage/current regulators, system power supplies 
etc.</li>
<li>A heat sink with thermal resistance not more than 2.40 <sup>o</sup>C/W must be fitted to the MSK5012.</li>
<li>Resistance R<sub>2</sub> is fixed at 10 K for all applications.</li>
<li>Quiescent current of MSK5012 is around 10mA.</li>
</ul>

10A Adjustable voltage Regulator MSK 5012

MSK5012 is a highly reliable adjustable voltage regulator.Whose output can be programmed using two resistors. The regulator has a very lo...

Battery eliminator circuit

Sunil Jadhavar 5:10 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
Here is the circuit diagram of a battery
 eliminator circuit that can be used as a replacement for 9V PP3 
batteries. The circuit given here can be used to power any device that 
operates from a 9V battery. The transformer T1 steps down the mains 
voltage and bridge D1 performs the job of rectification. Capacitor C1 is
 a filter. IC LM317T is the regulator here. The value of R1, R2 and R3 
are so selected that the output voltage of IC1 will be steady 9 volts.</div>
<div style="text-align: justify;">
<strong>Circuit diagram.</strong></div>
<div style="text-align: justify;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2009/12/battery-eliminator-circuit.png"><img alt="battery eliminator circuit" class="alignleft size-full wp-image-2732" height="263" src="http://www.circuitstoday.com/wp-content/uploads/2009/12/battery-eliminator-circuit.png" title="battery eliminator circuit" width="640" /></a></div>
<strong>Notes.</strong><br />

<ul>
<li>Assemble the circuit on a good quality PCB.</li>
<li>Transformer T1 can be a 230V primary, 9V secondary, 1.5A step down transformer.</li>
<li>If 1A Bridge is not available, then make one using four 1N 4007 diodes.</li>
<li>Do not connect loads that consume more than 1.5A to this circuit.</li>
<li>A heat sink is recommended for IC1.</li>
</ul>
<table><tbody>
<tr><td>

Battery eliminator circuit

Description. Here is the circuit diagram of a battery eliminator circuit that can be used as a replacement for 9V PP3 batteries. The ci...

Automatic changeover circuit

Sunil Jadhavar 5:10 AM

<div style="text-align: justify;">
<strong>Description.</strong><br />
The circuit diagram shown here is of a automatic changeover switch using
 IC LTC4412 from Linear Technologies. This circuit can be used for the 
automatic switchover of a load between a battery and a wall 
adapter.LTC4412 controls an external P-channel MOSFET to create a near 
ideal diode function for power switch over and load sharing. This makes 
the LT4412 an ideal replacement for power supply ORing diodes. A wide 
range of MOSFETs can be driven using the IC and this gives much 
flexibility in terms of load current. The LT4412 also has a bunch of 
good features like reverse battery protection, manual control input, 
MOSFET gate protection clamp etc.</div>
<div style="text-align: justify;">
The diode D1 prevents the reverse flow 
of current to the wall adapter when there is no mains supply. Capacitor 
C1 is the output filter capacitor. Pin 4 of the IC is called the status 
output. When wall adapter input is present the status output pin will be
 high and this can be used to enable another auxiliary P-channel MOSFET 
(not shown in the circuit diagram).<br />
<strong> </strong></div>
<div style="text-align: justify;">
<strong>Circuit diagram.</strong></div>
<div style="text-align: justify;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2010/01/automatic-changeover-circuit.png"><img alt="automatic changeover circuit" class="alignleft size-full wp-image-2931" height="305" src="http://www.circuitstoday.com/wp-content/uploads/2010/01/automatic-changeover-circuit.png" title="automatic changeover circuit" width="517" /></a></div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
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</div>
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</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
<strong>Notes.</strong></div>
<ul>
<li> Assemble the circuit on a good quality PCB.</li>
<li>The wall adapter input can be anything between 3 to 28V DC.</li>
<li>The battery voltage can be anything between 2.5V to 28V.</li>
<li>Do not connect loads that consume more than 2A.</li>
<li>Maximum continuous drain current of Q1 (FDN306P) is 2.5A.</li>
<li>D1 (1N5819 is a 1A Schottky diode.</li>
<li>Q1 (FDN306P) is a P-channel MOSFET.</li>
</ul>

Automatic changeover circuit

Description. The circuit diagram shown here is of a automatic changeover switch using IC LTC4412 from Linear Technologies. This circuit c...

12V battery level indicator circuit (LED bargraph)

Sunil Jadhavar 5:07 AM

<h4>
LM3914.</h4>
<div style="text-align: justify;">
The heart of this circuit is the LM3914 
from national semiconductors. The LM3914 can sense voltage levels and 
can drive a display of 10 LEDs in dot mode or bar mode. The bar mode and
 dot mode can be externally set and more than one ICs can be cascaded 
together to gat an extended display. The IC can operate from a wide 
supply voltage (3V to 25V DC). The brightness of the LEDs can be 
programmed using an external resistor. The LED outputs of LM3914 are TTL
 and CMOS compatible.</div>
<h4>
Description.</h4>
<div style="text-align: justify;">
In the circuit diagram LEDs D1 toD10 
displays the level of the battery in either dot or bargraph mode. 
Resistor R4 connected between pins 6,7 and ground controls the 
brightness of the LEDs. Resistors R1 and POT R2 forms a voltage divider 
network and the POT R2 can be used for calibration.</div>
<div style="text-align: justify;">
The circuit shown here is designed in 
order to monitor between 10.5V to 15V DC. The calibration of the circuit
 can be done as follows. After setting up the circuit connect a 12V DC 
source to the input. Now adjust the 10K POT to get the LED10 glow (in 
dot mode) or LEDs up to 10 glow (in bar mode). Now decrease the voltage 
in steps and at 10.5 volts only LED1 will glow. Switch S1 can be used to
 select between dot mode and bar graph mode. When S1 is closed, pin9 of 
the IC gets connected to the positive supply and bar graph mode gets 
enabled. When switch S1 is open pin9 of the IC gets disconnected to the 
positive supply and the display goes to the dot mode.</div>
<div style="text-align: justify;">
With little modification the circuit can
 be used to monitor other voltage ranges. For this just remove the 
resistor R3 and connect the upper level voltage to the input. Now adjust
 the POT R2 until LED 10 glows (in dot mode). Remove the upper voltage 
level and connect the lower level to the input. Now connect a high value
 POT (say 500K) in the place of R3 and adjust it until LED1 alone glows.
 Now remove the POT, measure the current resistance across it and 
connect a resistor of the same value in the place of R3. The level 
monitor is ready.</div>
<h4>
Circuit diagram of battery level indicator using LM3914.</h4>
<div class="wp-caption aligncenter" id="attachment_7080" style="width: 704px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/11/battery-level-indiactor.png"><img alt="" class="size-full wp-image-7080" height="468" src="http://www.circuitstoday.com/wp-content/uploads/2011/11/battery-level-indiactor.png" title="battery level indiactor" width="640" /></a><br />
<div class="wp-caption-text">
Battery level indicator circuit using LM3914</div>
</div>
<h4>
Cascading two LM3914.</h4>
Two or more LM3914 ICs can be cascaded together to get 
an extended display. The schematic of two LM3914 ICs cacaded together to
 get a 20 LED voltage level indicator is shown below.<br />
<div class="wp-caption aligncenter" id="attachment_7084" style="width: 728px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/11/cascading-two-LM3914.png"><img alt="20 LED voltage level indicator" class="size-full wp-image-7084" height="640" src="http://www.circuitstoday.com/wp-content/uploads/2011/11/cascading-two-LM3914.png" title="cascading two LM3914" width="622" /></a><br />
<div class="wp-caption-text">
Cascading two LM3914</div>
</div>
<h4>
<b>Few other battery level related circuits that you may like.</b></h4>
<div style="text-align: justify;">
1.<i><b>Simple battery level indicator</b></i>
 : This circuit can be used for monitoring the level of 3V batteries. 
The circuit is based on MN13811G from Panasonic. MN13811G is a CMOS 
 voltage detector IC that can be used a variety of voltage monitoring 
applications. In the circuit LED D1 will flash when ever the battery 
voltage drops below 2.4 volts.</div>
<div style="text-align: justify;">
2.<i><b>3 LED battery level indicator</b></i>
 : A 3 LED battery level indicator that can be used for monitoring the 
voltage level of 12V automobile battery is shown here. Three states of 
the battery ie; below 11.5V, between 11.5 and 13.5 and above 13.5 are 
shown by the glowing of LEDs.</div>
<div style="text-align: justify;">
3.<i><b> Flashing battery monitor</b></i>
 : This circuit can be used for monitoring the voltage level of 6 to 12V
 batteries. The circuit is based on transistors and the voltage level at
 which the LED starts flashing can be adjusted by using a potentiometer.</div>
<ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_2_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins>

12V battery level indicator circuit (LED bargraph)

LM3914. The heart of this circuit is the LM3914 from national semiconductors. The LM3914 can sense voltage levels and can drive a displ...

Chager circuit for SMF batteries

Sunil Jadhavar 5:05 AM

<strong>Description.</strong><br />

<div align="justify">
Here is a simple charger circuit for charging 
SMF(sealed maintenance free ) batteries.The charger circuit being 
curernt and voltage regulated,can be safely used to charge SMF batteries
 of 1.2 AH rating.This circuit was actually designed in response to a 
request from a reader.With slight modifications you can use it for 
charging any sort of SMF batteries.</div>
<div align="justify">
The first part of the circuit is the power supply 
made of transformer T1 and diodes D1&D2.The capacitor C1 filters the
 rectifier output .The next part is the section comprising of IC1 and Q1
 which provides the necessary volatge and current regulation.The diode 
D3 prevents ther reverse flow of charge from the battery .</div>
<div align="justify">
<strong>Circuit diagram with parts list.</strong></div>
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/06/smf-battery-charger-circuit.JPG" title="smf-battery-charger-circuit.JPG"><img alt="smf-battery-charger-circuit.JPG" height="314" src="http://www.circuitstoday.com/wp-content/uploads/2008/06/smf-battery-charger-circuit.JPG" width="640" /></a><br />

Notes.<br />

<ul>
<li>Assemble the circuit on a good quality PCB or common board.</li>
<li>An ammeter can be conncted in series with the battery to monitor the charging current.</li>
<li>Do not short circuit the charging terminals of the circuit.The circuit doesnot have short circuit protection.</li>
<li>R4 is the component that determines the charging current.Here it is 
set to be 120 mA. R4= (0.6 V/Charging current).By selecting the proper 
value of R4 according to equation, you can charge batteries that require
 different charging currents.</li>
</ul>
<ins style="border: none; display: inline-table; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"><ins id="aswift_2_anchor" style="border: none; display: block; height: 280px; margin: 0; padding: 0; position: relative; visibility: visible; width: 336px;"></ins></ins>

Chager circuit for SMF batteries

Description. Here is a simple charger circuit for charging SMF(sealed maintenance free ) batteries.The charger circuit being curernt an...

Super fast Ni-Cd battery charger

Sunil Jadhavar 5:03 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
<strong>H</strong>ere is  the circuit 
diagram of an effective and super fast Ni-Cd battery charger circuit.The
 circuit is based on the IC MAX 712. The circuit is designed to fast 
charge a Ni-Cd battery at 3oomA. After the fast charging is completed 
the circuit charges the battery in trickle charging mode at 15 mA. Here 
the instant to end fast charging and start trickle charging is sensed by
 dv/dt method as per the data sheet. This method of charging increases 
the charging speed as well as the battery life. The circuit is designed 
strictly as per the data sheet from Maxim and found to be working with 
no flaw.</div>
<div style="text-align: justify;">
<strong>T</strong>he diode D3 toD6 full 
wave rectifies the input supply. The capacitor C4 filters the output of 
the rectifier. The transistor Q1 (SK 100)  with associated components 
forms a series pass for driving the charging battery. The LED indicates 
the fast charging.</div>
<div style="text-align: justify;">
<strong>Circuit diagram with Parts list. </strong></div>
<div class="wp-caption aligncenter" id="attachment_7536" style="width: 625px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/04/Ni-Cd-Battery-CHarger-Circuit-Schematic.jpg"><img alt="Ni-Cd Battery Charger Circuit Diagram" class="size-full wp-image-7536" height="417" src="http://www.circuitstoday.com/wp-content/uploads/2008/04/Ni-Cd-Battery-CHarger-Circuit-Schematic.jpg" title="Ni-Cd Battery Charger Circuit Diagram" width="615" /></a><div class="wp-caption-text">
Ni-Cd Battery Charger Circuit Diagram</div>
</div>
<div style="text-align: justify;">
<strong>Notes.</strong></div>
<ul style="text-align: justify;">
<li>Assemble the circuit on a good quality PCB or common board.</li>
<li>Transistor 2N6109 can be also used instead of SK 100.</li>
<li>Do not connect not more than 2 Ni-Cd cells.</li>
<li>If you are using a PCB, it should be well designed and fabricated 
that there are no  unwanted feed back paths existing, which would cause 
oscillations in the circuit.</li>
</ul>

Super fast Ni-Cd battery charger

Description. H ere is the circuit diagram of an effective and super fast Ni-Cd battery charger circuit.The circuit is based on the IC ...

Simple battery charger circuit.

Sunil Jadhavar 5:02 AM

<strong>Description .</strong><br />

<strong>H</strong>ere is the circuit diagram of a simple and straight
 forward 12 V battery charger circuit with diagram. This circuit can be 
used to charge all type of 12V rechargeable batteries including car 
batteries. The circuit is nothing but a 12V DC power supply with an 
ammeter for monitoring the charging current. The two diodes forms a 
centre tapped full wave rectifier. The capacitor filters the rectifier 
output to produce a clean 12V output.<br />

<strong>Circuit diagram with Parts list. </strong><br />

<strong>Notes. </strong><br />

<ul>
<li>At initial stages of charging the ammeter will read about 1 to 3 amperes.</li>
<li>As the battery is slowly charged the current slowly decreases.</li>
<li>When the battery is fully charged the ammeter reading will be zero.</li>
<li><span style="color: red;">Always be careful to connect the charger to the battery in correct polarity. Positive to positive and negative to negative.</span></li>
</ul>

Simple battery charger circuit.

Description . H ere is the circuit diagram of a simple and straight forward 12 V battery charger circuit with diagram. This circuit can b...

Lead acid battery charger circuit

Sunil Jadhavar 5:00 AM

<h3 style="text-align: justify;">
<strong>Description</strong></h3>
<div style="text-align: justify;">
Here is a lead acid <strong>battery charger circuit</strong>
 using IC LM 317.The IC here provides the correct charging voltage for 
the battery.A battery must be charged with 1/10 its Ah value.This 
charging circuit is designed based on this fact.The charging current for
 the battery is controlled by Q1 ,R1,R4  and R5. Potentiometer R5 can be
 used to set the charging current.As the battery gets charged the the 
current through R1 increases .This changes the conduction of  Q1.Since 
collector of Q1 is connected to adjust pin of IC LM 317 the voltage at 
the output of of LM 317 increases.When battery is fully charged charger 
circuit reduces the charging current and this mode is called trickle 
charging mode.</div>
<h3 style="text-align: justify;">
<strong>Battery Charger Circuit Diagram with Parts List.</strong></h3>
<div class="wp-caption alignnone" style="width: 510px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/03/battery-charger.jpg" title="battery-charger.jpg"><img alt="Lead Acid Battery Charger" height="272" src="http://www.circuitstoday.com/wp-content/uploads/2008/03/battery-charger.jpg" title="Lead Acid Battery Charger Circuit" width="500" /></a><div class="wp-caption-text">
Lead Acid Battery Charger Circuit Diagram</div>
</div>
<div style="text-align: justify;">
</div>
<h3 style="text-align: justify;">
<strong>Notes .</strong></h3>
<ul style="text-align: justify;">
<li>Connect a battery to the circuit in series with a ammeter.Now adjust
 R5 to get the required charging current.  Charging current = (1/10)*Ah 
value of battery.</li>
<li>Input to the IC must be at least 18V for getting proper charging 
voltage at the output .Take a look at the data sheet of LM 317 for 
better understanding.</li>
<li>Fix LM317 with a heat sink.</li>
</ul>

Lead acid battery charger circuit

Description Here is a lead acid battery charger circuit using IC LM 317.The IC here provides the correct charging voltage for the batt...

Car Battery Voltmeter Circuit

Sunil Jadhavar 4:58 AM

<h3 style="text-align: justify;">
<strong>Description</strong></h3>
<div style="text-align: justify;">
This is a very useful circuit which when installed on your car gives the voltage of you <strong>car battery </strong>in
 a LED dot display form.The circuit  is based on four comparators made 
of quad op amp LM324.The inverting inputs of IC are kept at at reference
 voltages 5.6V,5.2V,4.8V,4.4V  respectively at pins 2,6,9,13  by 
resistors ,R3,R4,R5,R6.The battery voltage is directly fed to the pin 
inverting input through the voltage divider arrangement using R1 and 
R7.When there is variation in the input supply the out put of each op 
amp goes high accordingly as they are wired as voltage comparators.The 
corresponding LED glows.</div>
<h3 style="text-align: justify;">
<strong>Voltmeter Circuit Diagram and Parts List</strong></h3>
<div class="wp-caption alignnone" style="width: 625px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/03/led-volt-meter.jpg" title="led-volt-meter.jpg"><img alt="Voltmeter Circuit Diagram" height="395" src="http://www.circuitstoday.com/wp-content/uploads/2008/03/led-volt-meter.jpg" title="Voltmeter Circuit" width="615" /></a><div class="wp-caption-text">
Voltmeter Schematic</div>
</div>
<div style="text-align: justify;">
</div>
<h3 style="text-align: justify;">
<strong>Notes </strong></h3>
<ul style="text-align: justify;">
<li>IC LM 324 consists of4 op amps in one package , so power supply is common and is shown once (pin 4 and 11).</li>
<li>To setup , connect  the circuit to battery  ,adjust R6 so that 
required voltages are available at the inverting pins( refer description
 to get the required voltages).</li>
<li>Fix the LED’s on the dash board and mark the voltages near to it as shown in circuit diagram.The gadget is now ready.</li>
</ul>

Car Battery Voltmeter Circuit

Description This is a very useful circuit which when installed on your car gives the voltage of you car battery in a LED dot display for...

Simple Battery Level Indicator

Sunil Jadhavar 4:57 AM

<h3 style="text-align: justify;">
Description</h3>
<div style="text-align: justify;">
Here is a easy to build low battery 
level indicator circuit that produces a visible indication by flashing a
 LED when the battery voltage drops below a predetermined voltage.The 
circuit is based on Panasonic’s  IC MN13811G   and a efficient flasher 
based on transistors Q1&Q2.Here when the battery voltage drops below
 2.4  V the output of the IC is activated and the flasher starts 
flashing.This circuit here is an ideal one for monitoring the level of 
all types of 3V batteries.The circuit is power efficient with a  idle 
current drawing as less as 1 uA  , and a current drawing while flashing 
as less as 20uA.</div>
<h3 style="text-align: justify;">
<b>Circuit Diagram with Parts list .</b></h3>
<div class="wp-caption alignnone" style="width: 618px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/04/battery_-monitor-circuit.jpg" title="battery_-monitor-circuit.jpg"><img alt="Low Battery Level Indicator" height="376" src="http://www.circuitstoday.com/wp-content/uploads/2008/04/battery_-monitor-circuit.jpg" title="Battery Indicator Circuit" width="608" /></a><br />
<div class="wp-caption-text">
Battery Level Indicator Circuit Diagram</div>
</div>
<h3 style="text-align: justify;">
<b> Notes.</b></h3>
<div style="text-align: justify;">
Assemble the circuit on a good quality PCB or common board.</div>
<div style="text-align: justify;">
Do not keep the soldering iron tip on the IC’s pins for long time.</div>
<div style="text-align: justify;">
IC MN13811  series are available with 
different trip point voltages( from 2.4V t0 4.8V) ie MN13811G to 
MN13811U .If you need a trip point other than 2.4 shown here, you can 
choose the corresponding IC from the data sheet  and use it in the 
circuit here.</div>
<div style="text-align: justify;">
<b>We have more Battery Circuits that you may like to take a look;</b></div>
<div style="text-align: justify;">
<b>1. <a href="http://electroneecs-project.blogspot.in/2013/03/car-battery-voltmeter-circuit.html" title="Voltmeter Circuit">Voltmeter Circuit using LED</a></b></div>
<div style="text-align: justify;">
<b>2. <a href="http://electroneecs-project.blogspot.in/2013/03/lead-acid-battery-charger-circuit.html" title="Lead Acid Battery Charger">Lead Acid Battery Charger Circuit</a></b></div>
<div style="text-align: justify;">
<b>3. <a href="http://electroneecs-project.blogspot.in/2013/03/super-fast-ni-cd-battery-charger.html" title="Ni Cd Battery Charger">Ni Cd Battery Charger Circuit</a></b></div>
<div style="text-align: justify;">
<b>4. <a href="http://electroneecs-project.blogspot.in/2013/03/simple-battery-charger-circuit.html" title="Simple battery charger">Simple Battery Charger Circuit</a></b></div>
<div style="text-align: justify;">
<b>5. <a href="http://electroneecs-project.blogspot.in/2013/03/chager-circuit-for-smf-batteries.html" title="SMF Battery Charger">SMF Battery Charger</a></b></div>

Simple Battery Level Indicator

Description Here is a easy to build low battery level indicator circuit that produces a visible indication by flashing a LED when the b...

Fan speed controller using LM2941

Sunil Jadhavar 4:45 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
Many electronic circuits related to fan 
speed controlling have been published here and this one is just another 
approach. The circuit diagram shown here is of 12V DC fan speed 
controller using the IC LM2941CT which is a low drop out 1A voltage 
regulator. The IC has a dropout voltage as low as 0.5 and has also many 
useful features like power supply reverse protection, thermal 
protection, short circuit protection etc. The maximum output current the
 IC can source is 1A.<br />
The 12V DC supply is connected between the Vin (pin4) and ground (pin3) 
of the IC. The load, which is the fan, is connected across the Vout 
(pin5) and ground (pin3) of the IC. The network comprising of  
potentiometers R1, R2 and resistor determines adjust current (Iadj) of 
the IC. By varying the Iadj using the POT R2 we can adjust the output 
voltage of the IC and hence the fan speed.<br />
<strong>Circuit diagram.</strong></div>
<div style="text-align: justify;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2010/04/fan-speed-controller-using-LM2941.png"><img alt="fan speed controller using LM2941" class="alignleft size-full wp-image-3859" height="341" src="http://www.circuitstoday.com/wp-content/uploads/2010/04/fan-speed-controller-using-LM2941.png" title="fan speed controller using LM2941" width="653" /></a><br />
<strong> </strong></div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
<strong>Notes.</strong></div>
<ul>
<li> The circuit can be powered from 12V DC.</li>
<li>The maximum possible load current is 1A.</li>
<li>A heat sink is recommended for the IC.</li>
<li>POT R1 can be used to adjust the minimum fan speed.</li>
<li>POT R2 can be used to adjust the fan speed.</li>
</ul>
<div style="text-align: justify;">
</div>
<table><tbody>
<tr><td>

Fan speed controller using LM2941

Description. Many electronic circuits related to fan speed controlling have been published here and this one is just another approach. ...

Stepper motor controller

Sunil Jadhavar 4:45 AM

<strong>Description.</strong><br />

Here is the circuit diagram of a simple stepper motor controller 
using only elementary parts. The driver circuit uses, four transistor 
(SL100) to drive the motor windings, two NOT gates and one XOR gate to 
decode the two bit control logic to drive the four windings of the 
motor. The diodes D1 to D4 protects the corresponding transistors from 
transients generated during the switching of motor windings. d0 and d1 
are the control logics which determines the direction of rotation as 
well as speed.<br />

<strong>Circuit diagram with Parts list. </strong><br />

<strong>Notes.</strong><br />

<ul>
<li>The control logic for the circuit can be obtained from a 2 bit 
up/down counter clocked by a 555 astable multivibrator.The direction of 
count determines the direction of rotation and the frequency of astable 
multivibrator determines the speed of rotation.</li>
<li>As shown in the schematic above, IC1a IC1b belongs to same IC 7404.</li>
<li>Pin 14 and pin 7 of both IC1 and IC2 must be connected to +5 V and 
ground respectively, though it is not shown in circuit diagram.</li>
<li>The 5V can be obtained from a 7805 based power supply circuit.</li>
<li><a href="http://www.circuitstoday.com/?p=230" target="_blank" title="5V regulator using 7805 .Click here!."><span style="color: #333399;"><em><strong>5V power supply using IC 7805.Click Here.</strong></em></span></a></li>
<li>Vcc is the voltage required for the stepper motor. It varies from 
motor to motor. Here we can use up to 24V stepper motors. For higher 
operating voltages and power the SL100 transistors must be replaced with
 higher power transistors like 2N3055.</li>
</ul>
<em><strong>Truth table for clockwise rotation. </strong></em><br />

Stepper motor controller

Description. Here is the circuit diagram of a simple stepper motor controller using only elementary parts. The driver circuit uses, four ...

Temperature controlled DC fan

Sunil Jadhavar 4:43 AM

<strong>Description.</strong><br />

<div align="justify" class="MsoNormal">
Here is a simple circuit based on 
two transistors that can be used to control the speed of a 12 V DC fan 
depending on the temperature.A thermistor (R1) is used to sense the 
temperature. When the temperature increases the base current of Q1 (BC 
547) increases which in turn decreases the collector voltage of the same
 transistor. Since the collector of Q1 is coupled to the base of Q2 (BD 
140), the decrease in collector voltage of Q1 forward biases the Q2 more
 and so do the speed of the motor. Also, the brightness of the LED will 
be proportional to the speed of the motor.</div>
<strong>Circuit diagram with Parts list.</strong><br />

<strong>Notes.</strong><br />

<ul>
<li>The R1 can be a 15K @ 20°C ,N.T.C  thermistor.</li>
<li>The M1 can be a 12V,700mA fan motor.</li>
<li>The capacitor C1 must be rated 25V.</li>
<li>The circuit can be powered from a 12V PP3 battery or 12V DC power supply.</li>
<li>Assemble the circuit on a good quality PCB or common board.</li>
</ul>

Temperature controlled DC fan

Description. Here is a simple circuit based on two transistors that can be used to control the speed of a 12 V DC fan depending on the ...

Remote Operated Spy Robot Circuit

Sunil Jadhavar 4:36 AM

<div style="text-align: justify;">
Here is a remote operated spy robot 
circuit which can be controlled by using a wireless remote controller. 
It can capture audio and video information’s from the surroundings and 
can be sent to a remote station through RF signals. The maximum range is
 125 meters. It overcomes the limited range of infrared remote 
controllers. This robot consists of mainly two sections. They are 
explained in detail below.</div>
<div style="text-align: justify;">
<br /></div>
<div style="text-align: justify;">
<span style="font-size: large;"><b>Remote Control Operated Spy Robot Circuit – Block Diagram </b></span></div>
<div class="wp-caption alignnone" id="attachment_4361" style="width: 676px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/Remote-Control-Operated-Spy-Robot-Circuit1.jpg"><img alt="    Remote Control Operated Spy Robot Circuit - Block Diagram" class="size-full wp-image-4361 " height="455" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/Remote-Control-Operated-Spy-Robot-Circuit1.jpg" title="    Remote Control Operated Spy Robot Circuit - Block Diagram" width="666" /></a><div class="wp-caption-text">
    Remote Control Operated Spy Robot Circuit - Block Diagram</div>
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
<br /></div>
<div style="text-align: justify;">
<span style="font-size: small;"><strong>1. </strong><strong>Remote Control Section </strong></span></div>
<div style="text-align: justify;">
<br /></div>
<div style="text-align: justify;">
The circuit uses HT 12E, HT 12D encoder 
and decoder. 433MHz ASK transmitter and receiver is used for the remote 
control. H-bridge circuits are used for driving motors. Two 12V 
DC/100RPM gear motors are used as drivers. The working of the circuit is
 as follows.</div>
<div style="text-align: justify;">
When we are pressing any key in remote 
controller the HT 12E generate 8 bit address and 4 bit data .The DIP 
switches are used for setting the address. Then the ASK transmitter 
sends the 8 bit address and 4 bit data to the receiver Then the ASK 
receiver receives the 8 bit address and 4 bit data and HT 12D decoder 
decodes the data, thus enabling the appropriate output. Thus the output 
signals that are generated controls the H-bridge which then rotates the 
motors.</div>
<div style="text-align: justify;">
The 433 MHZ ASK transmitter and 
receivers are extremely small, and are excellent for applications 
requiring short-range RF remote controls.  The transmitter module is 
only 1/3<sup>rd</sup> the size of a standard postage stamp, and can 
easily be placed inside a small plastic enclosure. The transmitter 
output is up to 8mW at 433.92MHz. The transmitter accepts both linear 
and digital inputs and can operate from 1.5 to 12 Volts-DC, and makes 
building a miniature hand-held RF transmitter very easy.  The 433 MHZ 
ASK transmitters is approximately the size of a standard postage stamp</div>
<div style="text-align: justify;">
433 MHZ ASK receivers also operate at 433.92MHz, and have a sensitivity of 3uV.  The receiver operates from 4.5 to 5.5 volts-DC.</div>
<div style="text-align: justify;">
</div>
<div class="wp-caption aligncenter" id="attachment_4393" style="width: 599px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/Remote-Control-Operated-Spy-Robot-Circuit-Remote-Control-Section.jpg"><img alt="Remote-Control-Operated-Spy-Robot-Circuit-Remote-Control-Section" class="size-full wp-image-4393" height="566" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/Remote-Control-Operated-Spy-Robot-Circuit-Remote-Control-Section.jpg" title="Remote-Control-Operated-Spy-Robot-Circuit-Remote-Control-Section" width="589" /></a><div class="wp-caption-text">
Remote-Control-Operated-Spy-Robot-Circuit-Remote-Control-Section</div>
</div>
<div style="text-align: justify;">
</div>
<h3 style="text-align: justify;">
<span style="color: red;"></span></h3>
<div style="text-align: justify;">
<strong>2. </strong><strong>Video Transmission Section</strong></div>
<div style="text-align: justify;">
<br /></div>
<div style="text-align: justify;">
In this project we are using a wireless 
CCD camera. Now these types of cameras are commonly available in the 
market. It works on 12VDC supply.</div>
<div style="text-align: justify;">
To know more about CCD camera, click on the link below.</div>
<div style="text-align: justify;">
<strong>TAKE A LOOK : <span style="text-decoration: underline;">CHARGE COUPLED DEVICES (CCD)</span></strong></div>
<div style="text-align: justify;">
The 12 Volt DC supply is taken from the 
battery placed in the robot. The camera has a receiver, which is placed 
in the remote station. Its output signals are in the form of audio and 
video. These signals are directly connected to a TV receiver or a 
computer through a tuner card.</div>
<div style="text-align: justify;">
</div>
<div class="wp-caption aligncenter" id="attachment_4388" style="width: 902px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/Remote-Operated-Spy-Robot-Circuit1.jpg"><img alt="Remote Operated Spy Robot - Remote Control Section" class="size-full wp-image-4388" height="441" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/Remote-Operated-Spy-Robot-Circuit1.jpg" title="Remote-Operated-Spy-Robot-Circuit" width="640" /></a><div class="wp-caption-text">
Remote Operated Spy Robot - Remote Control Section</div>
</div>
<div style="text-align: justify;">
<strong>Components Required</strong></div>
<div style="text-align: justify;">
<br /></div>
<table border="1" cellpadding="0" cellspacing="0" style="text-align: justify;">
<tbody>
<tr>
<td valign="top" width="213">IC</td>
<td valign="top" width="213">HT 12E</td>
<td valign="top" width="213">1</td>
</tr>
<tr>
<td valign="top" width="213"><strong> </strong></td>
<td valign="top" width="213">HT 12D</td>
<td valign="top" width="213">1</td>
</tr>
<tr>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">LM 7805</td>
<td valign="top" width="213">2</td>
</tr>
<tr>
<td valign="top" width="213">TRANSISTOR</td>
<td valign="top" width="213">TIP 127</td>
<td valign="top" width="213">4</td>
</tr>
<tr>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">TIP 122</td>
<td valign="top" width="213">4</td>
</tr>
<tr>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">S 8050</td>
<td valign="top" width="213">4</td>
</tr>
<tr>
<td valign="top" width="213">DIODE</td>
<td valign="top" width="213">1N 4148</td>
<td valign="top" width="213">8</td>
</tr>
<tr>
<td valign="top" width="213">RESISTOR</td>
<td valign="top" width="213">1K</td>
<td valign="top" width="213">4</td>
</tr>
<tr>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">220E</td>
<td valign="top" width="213">4</td>
</tr>
<tr>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">39K</td>
<td valign="top" width="213">1</td>
</tr>
<tr>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">1M</td>
<td valign="top" width="213">1</td>
</tr>
<tr>
<td valign="top" width="213">ASK TRANSMITTER</td>
<td valign="top" width="213">433 MHz</td>
<td valign="top" width="213">1</td>
</tr>
<tr>
<td valign="top" width="213">ASK RECEIVER</td>
<td valign="top" width="213">433 MHz</td>
<td valign="top" width="213">1</td>
</tr>
<tr>
<td valign="top" width="213">DIP SWITCH</td>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">2</td>
</tr>
<tr>
<td valign="top" width="213">PUSH TO ON SWITCH</td>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">4</td>
</tr>
<tr>
<td valign="top" width="213">GEAR MOTOR</td>
<td valign="top" width="213">12V DC 100rpm</td>
<td valign="top" width="213">2</td>
</tr>
<tr>
<td valign="top" width="213">BATTERY</td>
<td valign="top" width="213">12V 1.3 Ah   rechargeable</td>
<td valign="top" width="213">1</td>
</tr>
<tr>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">9V</td>
<td valign="top" width="213">1</td>
</tr>
<tr>
<td valign="top" width="213">WIRELESS CCD CAMERA</td>
<td valign="top" width="213"><br /></td>
<td valign="top" width="213">1</td>
</tr>
</tbody>
</table>
<div style="text-align: justify;">
<br /></div>
<div style="text-align: justify;">
<strong>Construction</strong></div>
<div style="text-align: justify;">
The steps for the construction are…</div>
<div style="text-align: justify;">
1. Take a hylam sheet with (20cm*15cm) size.</div>
<div style="text-align: justify;">
2. Fix two gear motors (12VDC 100rpm) in the hylam sheet by using aluminum pieces and nut bolts as shown in the figure below.</div>
<div style="text-align: justify;">
3. Fix the ball castor as shown in the figure below.</div>
<div class="mceTemp" style="text-align: justify;">
<dl class="wp-caption alignnone" id="attachment_4338" style="width: 726px;">
<dt class="wp-caption-dt"><a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/CONSTRUCTION-OF-REM-OP-SPY.jpg"><img alt="Construction of Remote Operated Spy Robot Circuit " class="size-full wp-image-4338 " height="490" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/CONSTRUCTION-OF-REM-OP-SPY.jpg" title="Construction of Remote Operated Spy Robot Circuit " width="716" /></a></dt>
<dd class="wp-caption-dd">Construction of Remote Operated Spy Robot Circuit </dd></dl>
</div>
<div style="text-align: justify;">
4. Then fix the battery (12VDC 1.2Ah) on the top of the spy robot as shown in the figure below.</div>
<div class="mceTemp" style="text-align: justify;">
<dl class="wp-caption alignnone" id="attachment_4339" style="width: 628px;">
<dt class="wp-caption-dt"><a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/SPY-TOP-VIEW.jpg"><img alt="Construction of Remote Operated Spy Robot Circuit - Top View" class="size-full wp-image-4339" height="601" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/SPY-TOP-VIEW.jpg" title="Construction of Remote Operated Spy Robot Circuit - Top View" width="618" /></a></dt>
<dd class="wp-caption-dd">Construction of Remote Operated Spy Robot Circuit – Top View</dd></dl>
</div>
<div style="text-align: justify;">
5. Connect two motors to the PCB. The PCB is then connected to the battery.</div>
<div style="text-align: justify;">
6. Connect the wireless CCD camera to the battery.</div>
<div style="text-align: justify;">
7. Connect the camera receiver to the TV or computer. Video information’s will thus appear in the screen.</div>
<div style="text-align: justify;">
8. Switch on the remote controller and control the spy robot.</div>

Remote Operated Spy Robot Circuit

Here is a remote operated spy robot circuit which can be controlled by using a wireless remote controller. It can capture audio and video...

H bridge motor driver circuit

Sunil Jadhavar 4:32 AM

<div style="text-align: justify;">
<b>Description.</b><br />
The circuit given here is of a simple H bridge motor driver circuit 
using easily available components. H Bridge is a very effective method 
for driving motors and it finds a lot of applications in many electronic
 projects especially in robotics.</div>
<div style="text-align: justify;">
The circuit shown here is a typical four
 transistor H Bridge. The diodes D1 to D4 provide a safer path for the 
back emf from the motor to dissipate and thus it protects the 
corresponding bipolar transistors from damage. Resistors R1 to R4 limit 
the base current of the corresponding transistors. Working of this 
circuit is very easy to understand. When terminal D is grounded and A is
 pulled to +Vcc, transistors Q1 and Q4 will be on and current passes 
through the motor from left to right. When terminal B is grounded and C 
is pulled to +Vcc, transistors Q3 and Q2 will be on and current passes 
through the motor from right to right making the motor to rotate in the 
opposite direction.</div>
<b>Circuit diagram.</b><br />
<div style="text-align: center;">
<div class="separator" style="clear: both; text-align: center;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/h-bridge-motor-driver.png" style="margin-left: 1em; margin-right: 1em;"><img alt="" class="size-full wp-image-4416 aligncenter" height="252" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/h-bridge-motor-driver.png" title="h bridge motor driver" width="400" /></a></div>
<b><br />
</b></div>
<div style="text-align: center;">
<div class="separator" style="clear: both; text-align: center;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/h-bridge-motor-driver-circuit.png" style="margin-left: 1em; margin-right: 1em;"><img alt="" class="size-full wp-image-4397 aligncenter" height="226" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/h-bridge-motor-driver-circuit.png" title="h bridge motor driver circuit" width="400" /></a></div>
</div>
<b>Notes.</b><br />
<ul>
<li>The circuit can be assembled on a Vero board.</li>
<li>The maximum possible collector current of 2N2222 is 800mA and that for 2N2907 is 600mA.</li>
<li>A DC brush type motor is used here.</li>
<li>Do not use a motor that draws more than 600mA of current.</li>
<li>+Vcc can be anything between 3 to 15V DC depending on the voltage rating of the motor used.</li>
<li>Do not connect terminal D to ground and C to +Vcc same time, it will result in short circuit.</li>
<li>Do not connect terminal B to ground and C to +Vcc same time, it will also result in short.</li>
<li>Resistors R1 to R4 limit the base current of the corresponding 
transistors. By altering their value, you can alter the motor current.</li>
</ul>

H bridge motor driver circuit

Description. The circuit given here is of a simple H bridge motor driver circuit using easily available components. H Bridge is a very ef...

H Bridge motor control circuit using L298

Sunil Jadhavar 4:31 AM

<h3 style="text-align: justify;">
<b>Description :</b></h3>
<div style="text-align: justify;">
A bidirectional <a href="http://www.circuitstoday.com/h-bridge-motor-driver-circuit"><b>H bridge</b></a><b> </b>DC
 motor control circuit is shown here. The circuit is based on the IC 
L298 from ST Microelectronics. L298 is a dual full bridge driver that 
has a wide operating voltage range and can handle load currents up to 
3A. The IC also features low saturation voltage and over temperature 
protection.<br />
In the circuit diode D1 to D4 are protection diodes. Capacitor C2 is the
 logic power supply filter and capacitor C2 is the supply voltage 
filter. The state of the motor will depend on the logic level of the 
pins 10, 11, 12 and it is described in the table shown below the circuit
 diagram.</div>
<div style="text-align: justify;">
</div>
<h3 style="text-align: justify;">
<b>Circuit diagram of H bridge motor controller:<br />
</b></h3>
<div class="wp-caption aligncenter" id="attachment_4489" style="width: 587px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/h-bridge-motor-control-circuit-using-L298.png"><img alt="H Bridge Motor Control Driver Circuit Schematic using IC L298" class="size-full wp-image-4489 " height="536" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/h-bridge-motor-control-circuit-using-L298.png" title="H Bridge Motor Driver Circuit Schematic" width="577" /></a><br />
<div class="wp-caption-text">
H Bridge Motor Control Circuit Schematic</div>
</div>
<div style="text-align: center;">
<br /></div>
<div style="text-align: justify;">
</div>
<div class="wp-caption aligncenter" style="width: 472px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/01/h-bridge-motor-driver1.png"><img alt="H bridge motor control" height="217" src="http://www.circuitstoday.com/wp-content/uploads/2011/01/h-bridge-motor-driver1.png" title="h bridge motor driver " width="462" /></a><br />
<div class="wp-caption-text">
H Bridge Motor Driver-Inputs</div>
</div>
<div style="text-align: center;">
</div>
<h3 style="text-align: justify;">
<b>Notes :<br />
</b></h3>
<ul>
<li>Do not connect a motor that consumes more than 2.5A of current.</li>
<li>The main power supply can be anything between 3 to 40V DC.</li>
<li>It is advised to fit LM298 with a proper heat sink.</li>
</ul>
<b>We have more articles of your interest related to H-Bridge:</b><br />
<b>1. <a href="http://electroneecs-project.blogspot.in/2013/03/h-bridge-motor-driver-circuit.html">H Bridge Motor Driver Circuit</a></b><br />
<b>2. <a href="http://electroneecs-project.blogspot.in/2013/03/remote-operated-spy-robot-circuit.html">Remote Operated Spy Robot</a></b>

H Bridge motor control circuit using L298

Description : A bidirectional H bridge DC motor control circuit is shown here. The circuit is based on the IC L298 from ST Microelectr...

DC motor control circuit using NE555

Sunil Jadhavar IC555 Project 4:30 AM

<h3>
<b>Description.</b></h3>
<div style="text-align: justify;">
A simple DC motor controller circuit using NE555 is shown here. Many <a href="http://www.circuitstoday.com/pwm-motor-speed-controller" target="_blank">DC motor speed control</a>
 circuits have been published here but this is the first one using NE555
 timer IC. In addition to controlling the motors speed its direction of 
rotation can be also changed using this circuit.</div>
<div style="text-align: justify;">
A PWM circuit based on timer NE555 is 
the heart of this circuit. NE555 is wired as an astable multivibrator 
whose duty cycle can be adjusted by varying the POT R1. The output of 
IC1 is coupled to the base of transistor Q1 which drives the motor 
according to the PWM signal available at its base. Higher the duty cycle
 the average voltage across motor will be high which results in higher 
motor speed and vice versa. Change of DC motor direction is attained 
using the DPDT switch S1 which on application just toggles the polarity 
applied to the motor.</div>
<b> </b><br />
<h3>
<b>Circuit diagram of DC motor controller.</b></h3>
<div class="mceTemp">
<b> </b>
<br />
<div class="wp-caption alignleft" id="attachment_4948" style="width: 862px;">
<b><a href="http://www.circuitstoday.com/wp-content/uploads/2011/02/dc-motor-controller.png"><img alt="Dc motor control circuit diagram" class="size-full wp-image-4948 " height="363" src="http://www.circuitstoday.com/wp-content/uploads/2011/02/dc-motor-controller.png" title="dc motor controller" width="640" /></a></b><br />
<div class="wp-caption-text">
DC motor controller using NE555</div>
</div>
<b>Notes.</b></div>
<ul>
<li>The circuit can be assembled on a Vero board or PCB.</li>
<li>Use 12V DC for powering the IC.</li>
<li>Vm is the power supply for motor and its value depends on the motors
 voltage rating. Any way maximum Vceo for BD139 is 80V and so Vm should 
not be exceeded 80 volts.</li>
<li>Maximum collector current BD139 can handle is 1.5A and so do not use a motor that consumes more than 1.5 amperes of current.</li>
<li>A heat sink is necessary for BD139.</li>
</ul>
<b>Few other  DC motor speed control circuit you may be interested in:</b>

DC motor control circuit using NE555

Description. A simple DC motor controller circuit using NE555 is shown here. Many DC motor speed control circuits have been published h...

Low cost AM radio

Sunil Jadhavar 4:28 AM

<div style="text-align: justify;">
<strong>Description.</strong><br />
Here is the circuit diagram of a simple and low cost AM radio. The 
working of this radio circuit is straight forward. Inductor L1 and 
capacitor C1 forms the necessary tank circuit. Diode D1 performs the job
 of de-modulation. Transistor T1 is wired as a preamplifier whose output
 is further amplified by the IC LM386 to drive the head phone Z1. The 
10K POT R3 can be used as a volume controller.<br />
<strong>Circuit diagram.</strong></div>
<div style="text-align: justify;">
<strong><a href="http://www.circuitstoday.com/wp-content/uploads/2009/09/low-cost-am-radio.png"><img alt="low cost am radio" class="alignleft size-full wp-image-2108" height="291" src="http://www.circuitstoday.com/wp-content/uploads/2009/09/low-cost-am-radio.png" title="low cost am radio" width="640" /></a><br />
</strong></div>
<strong>Notes.</strong><br />

<ul>
<li> The circuit can be powered from a 9V PP3 battery.</li>
<li>Use a 100cm long metal wire as antenna.</li>
<li>Experiment with the value of L1 for catching other bands.</li>
<li>The circuit can be assembled on a Vero board.</li>
</ul>

Low cost AM radio

Description. Here is the circuit diagram of a simple and low cost AM radio. The working of this radio circuit is straight forward. Induct...

FM adaptor circuit for car stereo

Sunil Jadhavar 4:25 AM

<strong>Description.</strong><br />

<div align="justify">
<strong>W</strong>ith this compact FM adaptor circuit
 plugged into the audio out of your cassete player or i Pod out put,you 
can listen your favorite music on your car stereo.This circuit is very 
useful if your car stereo doesnot have an auxillary in socket.The 
circuit is nothing buy  an short range  FM transimitter.</div>
<div align="justify">
The FM transmitter circuit is based on low power NPN 
transistor 2N2222.The tank circuit consisting of L1 & C1 producess 
the necessary oscillations at the collector of Q1.The capacitance C4 , 
resistance R3 & R4  performs the function of mixing the stereo out 
put from theaudio player or i-Pod.The emitter resistance R2 provides 
sufficient stability to the circuit.It also limits the collector current
 to increse the battery life.</div>
<strong>Circuit diagram with Parts list.</strong><br />

<strong>Notes.</strong><br />

<ul>
<li>Use a 28SWG , 10 cm insulated copper wire as antenna.</li>
<li>For L1.make 8 turns of 20 SWG insulated copper wire on a 5mm dia plastic former.</li>
<li>Power the circuit from a 3V battery.</li>
<li>Assemble the circuit on a good quality PCB or common board.</li>
<li>C1 can be a  50pF trimmer.</li>
</ul>

FM adaptor circuit for car stereo

Description. W ith this compact FM adaptor circuit plugged into the audio out of your cassete player or i Pod out put,you can listen yo...

AN7415 FM Stereo Demodulator

Sunil Jadhavar 4:24 AM

<div style="text-align: justify;">
AN7415 is a monolithic integrated 
circuit that can be used in FM stereo demodulation applications. The 
operating voltage range is 1.6 to 7Vdc. Two AA dry cells are enough for 
powering this IC and it makes the AN7415 suitable for handheld FM radio 
applications. AN7415 has low current consumption (2.6mA), low 
distortion, good channel separation and high gain. The IC is available 
in 16 pin DIL package.</div>
<h3 style="text-align: justify;">
Description.</h3>
<div style="text-align: justify;">
The circuit shown below is of a PLL FM 
stereo demodulator designed based on the AN7415. C1 is the input 
coupling capacitor which blocks any DC voltage present in the 
multiplexed input signal. LED D1 is an indicator LED and R1 is its 
current limiting resistor. C4 and C5 are the DC decoupling capacitors 
for the left and right output channels. C2 and C3 are the noise bypass 
capacitors for the left and right output channels. POT R2 can be used 
for adjusting the channel separation. Resistor R5 and capacitors C7 and 
C8 forms a low-pass filter network for the internal DC amplifier 
circuitry (see the block diagram of AN7415). C10 is a filter capacitor 
for the IC’s internal Schmitt trigger amplifier circuitry.  C9 is a 
ripple filter capacitor for the voltage stabilizer circuit inside the 
AN7415. Resistor R3, POT R4 and Capacitor C6 sets the time constant of 
the internal VCO circuit. Hence POT R4 can be used for adjusting the VCO
 frequency. A 19KHz frequency check signal is available at the PIN 12 of
 the IC. Switch S1 can be used for enabling and disabling forced mono 
function.</div>
<h3 style="text-align: justify;">
Circuit diagram.</h3>
<div class="wp-caption aligncenter" id="attachment_6569" style="width: 843px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/10/AN7415-stereo-decoder.png"><img alt="fm stereo decoder" class="size-full wp-image-6569" height="481" src="http://www.circuitstoday.com/wp-content/uploads/2011/10/AN7415-stereo-decoder.png" title="AN7415 stereo decoder" width="640" /></a><div class="wp-caption-text">
AN7415 stereo decoder</div>
</div>
<h3 style="text-align: justify;">
Notes.</h3>
<ul>
<li>Well designed and good quality PCB improves the performance.</li>
<li>Input supply voltage range is from 1.6V to 7VDC.</li>
<li>I recommend 3VDC for powering the circuit.</li>
<li>POT R4 can be used for adjusting the voltage controlled oscillator (VCO) frequency.</li>
<li>POT R2 can be used for setting the channel separation.</li>
<li>Recommended LED indicator current is 40mA.</li>
<li>Maximum power dissipation is 80mW.</li>
</ul>

AN7415 FM Stereo Demodulator

AN7415 is a monolithic integrated circuit that can be used in FM stereo demodulation applications. The operating voltage range is 1.6 to ...

PLL FM demodulator circuit

Sunil Jadhavar FM Transmitter Circuits 4:23 AM

<div style="text-align: justify;">
A simple PLL FM demodulator circuit 
using IC XR2212 is shown here. XR2212 is a highly stable, monolithic PLL
 (phase locked loop) IC specifically designed for communication and 
control system applications. The IC has 0.01 Hz to 300KHz frequency 
range, 4.5 to 20V operating voltage range, 2mV to 3Vrms dynamic range, 
high temperature range, TTL / CMOS compatibility and adjustable tracking
 range. The block diagram of a typical PLL FM demodulator circuit is 
shown below.</div>
<div class="wp-caption aligncenter" id="attachment_7472" style="width: 661px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2012/02/PLL-FM-demodulator-block-diagram.png"><img alt="PLL bloack diagram" class="size-full wp-image-7472" height="351" src="http://www.circuitstoday.com/wp-content/uploads/2012/02/PLL-FM-demodulator-block-diagram.png" title="PLL FM demodulator block diagram" width="651" /></a><div class="wp-caption-text">
PLL FM demodulator block diagram</div>
</div>
<div style="text-align: justify;">
The working of a PLL FM demodulator is 
very easy to understand.The input FM signal and the output of the VCO is
 applied to the phase detector circuit. The output of the phase detector
 is filtered using a low pass filter, the amplifier and then used for 
controlling the VCO. When there is no carrier modulation and the input 
FM signal is in the center of the pass band (i.e. carrier wave only) the
 VCO’s tune line voltage will be at the center position. When deviation 
in carrier frequency occurs ( that means modulation occurs) the VCO 
frequency follows the input signal in order to keep the loop in lock. As
 a result the tune line voltage to the VCO varies and this variation is 
proportional to the modulation done to the FM carrier wave. This voltage
 variation is filtered and amplified in order to get the demodulated 
signal.</div>
<h4 style="text-align: justify;">
Circuit diagram.</h4>
<div class="wp-caption aligncenter" id="attachment_7470" style="width: 879px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2012/01/PLL-FM-demodulator-circuit-XR2212.png"><img alt="PLL fm demodulator" class="size-full wp-image-7470" height="362" src="http://www.circuitstoday.com/wp-content/uploads/2012/01/PLL-FM-demodulator-circuit-XR2212.png" title="PLL FM demodulator circuit XR2212" width="640" /></a><div class="wp-caption-text">
PLL FM demodulator</div>
</div>
<div style="text-align: justify;">
Composite FM signal is applied to pin 2 
of the IC. Input impedance of this pin is around 20K and the voltage 
swing of the input signal must be between 10mV to 5V. Capacitor C5 is 
meant for frequency compensating the internal output opamp. The 
capacitor C5 is connected between pin 6 and 8 of the IC and its value 
can be 20 to 30pF. Co is the timing capacitor for the internal voltage 
controlled oscillator (VCO). The VCO frequency is inversely proportional
 to the value of the timing capacitor Co and its range can be 200pF to 
10uF. C4 is the input supply by-pass capacitor. Free running frequency 
of the VCO is determined by the external timing resistor Ro. Value of Ro
 can be between 10 and 100K. Rx can used for fine tuning the VCO 
frequency. R1 and C1 forms a PLL loop filter. Resistors Rf and Rc sets 
the gain of the output amplifier section.</div>
<h4>
Design.</h4>
<ol>
<li>Center frequency of the voltage controlled oscillator (VCO) , fo must be selected equal to the frequency of the FM carrier wave.</li>
<li>Value of Ro can be in the range 10K to 100k and the recommended value is 20K.</li>
<li>Co = 1/Rofo</li>
<li>C1 = Co/4.</li>
<li>Rf can be taken as 100K and RC can be taken as 80.6K for a +/-4V output swing.</li>
<li>R1 can be taken as 89.3K.</li>
</ol>

PLL FM demodulator circuit

A simple PLL FM demodulator circuit using IC XR2212 is shown here. XR2212 is a highly stable, monolithic PLL (phase locked loop) IC speci...

FM Tracking transmitter

Sunil Jadhavar FM Transmitter Circuits 4:22 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
<strong>T</strong>he circuit presented 
her will transmit a audio tone in the FM  band. The circuit can be used 
as a tracking signal transmitter or a remote control transmitter. The 
circuit uses only easily available components and any one can build 
this. The transmitter has a range of 100m @ 9V supply, with a matching 
antenna.<br />
The NE555 timer (IC1) is used for producing the audio tone. The first 
JFET (Q1) is wired as a Hartley oscillator which is frequency modulated 
by the audio tone. The second (Q2) JFET is wired as a buffer to isolate 
the oscillator based on Q1 from the antenna. The diode D1 is used as a 
varactor here. The diode is reverse biased by the ramping voltage 
produced at the pin 6&2 of the IC1. This results in the change of 
junction capacitance of reverse biased diode, which in turn alters the 
frequency of the oscillator to attain the frequency modulation.</div>
<div style="text-align: justify;">
<strong>Circuit diagram with Parts  list. </strong></div>
<div style="text-align: justify;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/05/fm-tracking-transmitter.JPG" title="fm-tracking-transmitter.JPG"><img alt="fm-tracking-transmitter.JPG" height="286" src="http://www.circuitstoday.com/wp-content/uploads/2008/05/fm-tracking-transmitter.JPG" width="573" /></a></div>
<div style="text-align: justify;">
<strong>Notes. </strong></div>
<ul style="text-align: justify;">
<li>The inductor L1 can be made by winding 5 turns of  18 SWG enameled 
copper wire on a 3/8 inch long, 3/16 inch diameter plastic tube. The 
coil must be tapped at the center.</li>
<li>The antenna can be a 20cm long wire.</li>
<li>The circuit can be powered from a 9V battery.</li>
<li>POT R6 can be used to adjust the transmission power.</li>
</ul>

FM Tracking transmitter

Description. T he circuit presented her will transmit a audio tone in the FM band. The circuit can be used as a tracking signal transm...

Single chip FM transmitter circuit

Sunil Jadhavar FM Transmitter Circuits 4:21 AM

<h3 style="text-align: justify;">
<strong>Description</strong></h3>
<div style="text-align: justify;">
<strong>H</strong>ere’s a single chip FM
 transmitter circuit using Maxim semiconductors IC MAX2606. The MAX2606 
is a compact, high-performance  intermediate frequency VCO specially 
designed for wireless communication circuits. They have monolithic 
construction with low-noise and a low-power operation in a compact  
6-pin SOT23 packing .Th1s low-noise IC feature an on-chip varicap diode 
and feedback capacitances that avoid the need for external tuning 
components, making the MAX2606 perfect for portable systems. Only an 
external inductor is needed to set the oscillation frequency.In addition
 to this, an<br />
integrated differential output buffer  is also there for driving a mixer
 or prescaler.The MAX2606 can be  operated  from a single +2.8 V to 
+5.4V supply and consumes very less current .The chip can be operated 
from 45MHz to 650MHz .</div>
<div style="text-align: justify;">
In the circuit the  nominal frequency is
 set to 100 Mhz  by inductor L1, (390nH) . The  left and right channel  
audio signals from your source  are added by R3 and R4, and attenuated 
by the POT  R2. R2 can be used as a volume control .POT R1 can be used 
to select a channel of transmission between 88Mhz and 108Mhz.Use 80 cm 
long wire as the antenna .</div>
<h3 style="text-align: justify;">
<strong>FM Transmitter Circuit Diagram with Parts List. </strong></h3>
<div class="wp-caption alignnone" style="width: 610px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2008/03/max2606_single_chip_transmitter.JPG" title="max2606_single_chip_fm_transmitter circuit.JPG"><img alt="Single Chip FM Transmitter " height="340" src="http://www.circuitstoday.com/wp-content/uploads/2008/03/max2606_single_chip_transmitter.JPG" title="Single Chip FM Transmitter Circuit" width="600" /></a><div class="wp-caption-text">
Single Chip FM Transmitter Circuit Diagram</div>
</div>
<div style="text-align: justify;">
<br /></div>
<h3 style="text-align: justify;">
Notes</h3>
<ul style="text-align: justify;">
<li>Assemble the circuit on a good quality PCB or common board.</li>
<li>Use a battery for powering the circuit.It will reduce noise.</li>
<li>An FM antenna from a old radio is a better option than the wire antenna.</li>
</ul>

Single chip FM transmitter circuit

Description H ere’s a single chip FM transmitter circuit using Maxim semiconductors IC MAX2606. The MAX2606 is a compact, high-performa...

Telephone transmitter

Sunil Jadhavar 4:21 AM

<strong>Description.</strong><br />

<div style="text-align: justify;">
This is a simple, but very useful 
circuit that can be used to transmit telephone conversations. When the 
telephone receiver is on hook the voltage across the lines will be about
 48 volts. The preset R7 is so adjusted to obtain a 24.7 V across 
between the cathode of D2 and ground. At this voltage the Zener diode D2
 will be in breakdown and the transistor T1 will conduct. This makes the
 transistor T2 OFF. When the receiver is off hook, the line voltage 
drops to about 11 volts. This makes the transistor T1 OFF and 
subsequently the T2 ON. The T2 in switched ON condition will provide a 
DC path for the transistor T3 used in the FM transmitter section.</div>
<div style="text-align: justify;">
The transistor T3 is wired as a common 
emitter radio frequency oscillator. In simple words the transistor T2 
serves as an ON/OFF switch for this oscillator. The modulated signal 
will be available at the collector of transistor T3 and the signal id 
fed to the antenna via capacitor C5.</div>
<strong>Circuit diagram with Parts list.</strong><br />

<strong>Notes.</strong><br />

<ul>
<li>Assemble the circuit on a good quality PCB.</li>
<li>For L1 make 45 turns of 36 SWG enameled copper wire on the resistor R6 itself.</li>
<li>The resistor R6 must be a 1M, 1 watt resistor.</li>
<li>For L2 make 3 turns of 21 SWG enameled copper wire on a 12 mm plastic former.</li>
<li>For antenna, use a 1 meter insulated copper wire.</li>
<li>The capacitor C3 can be a 50pF trimmer.</li>
</ul>

Telephone transmitter

Description. This is a simple, but very useful circuit that can be used to transmit telephone conversations. When the telephone receive...

CXA1019 FM receiver circuit

Sunil Jadhavar FM Transmitter Circuits 4:19 AM

<div style="text-align: justify;">
A high quality FM receiver circuit based
 on CXA1019 IC is shown here. CXA1019 is a bipolar silicon monolithic 
FM/AM radio receiver IC from Sony. Built in circuitries inside the 
CXA1019 include RF amplifier, mixer, oscillator, IF amplifier, 
quadrature detection circuit, tuning LED driver electronic volume 
control, detector etc. FM section of the IC is only utilized in this 
circuit. The IC can be powered from anything between 3 to 7V DC and can 
drive an 8 ohm loudspeaker.</div>
<h3>
Circuit diagram.</h3>
<div class="wp-caption aligncenter" id="attachment_6329" style="width: 1028px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/08/FM-radio-reveiver-circuit.png"><img alt="FM receiver circuit" class="size-full wp-image-6329" height="526" src="http://www.circuitstoday.com/wp-content/uploads/2011/08/FM-radio-reveiver-circuit.png" title="FM radio reveiver circuit" width="640" /></a><div class="wp-caption-text">
FM receiver circuit CXA1019</div>
</div>
<h3>
Circuit description.</h3>
<div style="text-align: justify;">
Inductors L1, L2 and capacitors C4, C6, 
C7 forms the tank circuit for the ICs built in oscillator section. The 
IF output available at pin 15 is grounded through resistor R1. C1 is the
 AC bypass capacitor for R1. Capacitor C16 is meant for ripple 
filtering. LED D1 is a tuning indicator. Output of the built-in detector
 stage (pin24) is coupled to the input (pin 25) of the built in AF 
amplifier stage through capacitor C19, POT R2 and capacitor C18. The POT
 R2 can be used as a volume control because it controls the input given 
to the audio amplifier stage. Capacitor C15 couples the audio output to 
the speaker and C14 is a noise bypass capacitor. C5 is just a power 
supply filter while C20 couples the antenna to the FM RF input (pin13) 
of the IC. The FM intermediate frequency output available at pin 15 is 
filtered using the 10MHz ceramic filter and applied to the FM 
intermediate frequency input pin18. Capacitor C2 is used for bypassing 
noise from the audio power amplifier section inside the IC. The output 
of this power amplifier section is around 500mW. Capacitor C1 and 
transformer T1 are related to the FM discriminator circuitry inside the 
IC. Resistor R3 is the feedback capacitor for the AGC section.</div>
<h3 style="text-align: justify;">
Notes.</h3>
<ul>
<li>Assemble the circuit on a good quality PCB.</li>
<li>For L1, make 2.75 turns of 22 SWG enamelled copper wire on a 5mm diameter plastic former.</li>
<li>For L2, make 3.75 turns of 22 SWG enamelled copper wire on a 5mm plastic former.</li>
<li>T1 is a FM IF transformer.</li>
<li>CF1 is a 10.7MHz FM ceramic filter</li>
<li>C4 is a 30pF dual gang FM tuning capacitor.</li>
<li>The circuit can be powered from anything between 3V to 7V DC.</li>
<li>Using a battery for powering the circuit will reduce noise and improve the performance</li>
<li>If you using a battery eliminator, then it must be well regulated and free from noise.</li>
<li>K1 can be a 3W, 8 ohm loudspeaker.</li>
<li>A1 can be a 100cm long whip antenna.</li>
</ul>

CXA1019 FM receiver circuit

A high quality FM receiver circuit based on CXA1019 IC is shown here. CXA1019 is a bipolar silicon monolithic FM/AM radio receiver IC fro...

Simplest FM Transmitter

Sunil Jadhavar FM Transmitter Circuits 4:19 AM

<div style="text-align: justify;">
<strong>Description.</strong></div>
<div style="text-align: justify;">
<strong>H</strong>ere is the circuit 
diagram of the simplest FM transmitter using a transistor. Great 
performance or range is not guaranteed here, because this is an 
elementary design. General purpose radio frequency transistor BF 494 
(Q1) is used here for obtaining FM modulation. A condenser mic is used 
here to pickup the sound. The condenser mic converts the sound to 
electrical variations and this variations are fed to the base of Q1, 
which performs the amplification as well as modulation. The capacitor  
C2  and L1 determines the frequency of transmission. The circuit can be 
powered from a 9V transistor radio battery.</div>
<div style="text-align: justify;">
<strong>Circuit diagram and Parts list. </strong> <a href="http://www.circuitstoday.com/wp-content/uploads/2008/04/fm-transmitter-circuit.JPG" title="fm-transmitter-circuit.JPG"><img alt="fm-transmitter-circuit.JPG" height="319" src="http://www.circuitstoday.com/wp-content/uploads/2008/04/fm-transmitter-circuit.JPG" width="605" /></a> <strong>Notes. </strong></div>
<ul style="text-align: justify;">
<li>The coil L1 can be made by winding 8 turns of 1mm thick enamel 
coated copper wire on a ball pen refill.  The coil should be tapped  at 
the  center for connecting the antenna.</li>
<li>A 30 cm wire can be used as an antenna.</li>
<li>Remember! This circuit is an elementary circuit. No good performance
 or range is not guaranteed. Ideal for demo applications only. I got 
only 8 meter range with some decent sound quality.</li>
<li>Battery is strictly recommended because mains powered supply may induce additional noise.</li>
</ul>

Simplest FM Transmitter

Description. H ere is the circuit diagram of the simplest FM transmitter using a transistor. Great performance or range is not guarante...

FM Radio jammer

Sunil Jadhavar FM Transmitter Circuits 4:18 AM

<div style="text-align: justify;">
<strong>Description.</strong><br />
Circuit shown here can be used to jam FM radios in its vicinity. The 
circuit is nothing but a classic single transistor oscillator operating 
in the VHF region. Working principle of the circuit is very simple and 
straight forward. Powerful VHF oscillations from the circuit will 
interfere with the FM signals to nullify it. Jammer circuits like this 
are illegal in many countries and you must assemble this circuit on your
 own responsibility. This circuit is intended only for fun and i request
 you not to misuse it.<br />
<strong>Circuit diagram.</strong></div>
<div style="text-align: justify;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2009/12/FM-radio-jammer.png"><img alt="FM radio jammer" class="alignleft size-full wp-image-2724" height="339" src="http://www.circuitstoday.com/wp-content/uploads/2009/12/FM-radio-jammer.png" title="FM radio jammer" width="524" /></a><br />
<strong> </strong></div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
<strong>Notes.</strong></div>
<ul>
<li> For L1 make 6 turns of 16AWG enamelled copper wire on a 9mm plastic former.</li>
<li>The circuit can be powered using a 9V PP3 battery.</li>
<li>For extended range, use an antenna.</li>
<li>A 30cm long wire connected anywhere on the coil will do for the antenna.</li>
<li>For better performance, assemble the circuit on a good PCB.</li>
</ul>

FM Radio jammer

Description. Circuit shown here can be used to jam FM radios in its vicinity. The circuit is nothing but a classic single transistor osci...

Miniature FM transmitter

Sunil Jadhavar FM Transmitter Circuits 4:17 AM

<div style="text-align: justify;">
<strong>Description.</strong><br />
This could be the simplest FM transmitter circuit you can find on the 
internet. Only using a single transistor and few passive components, 
this transmitter can deliver signals up to 50 meters. The transistor Q1 
serves as the modulator as well as oscillator. Capacitor C2 and inductor
 L1 forms the necessary tank circuit for making oscillation. The voice 
to be transmitted is coupled to the base of Q1 using an electret 
microphone. The FM signal available at the collector of Q1 is radiated 
using the antenna.<br />
<strong>Circuit diagram.</strong></div>
<div style="text-align: justify;">
<strong><a href="http://www.circuitstoday.com/wp-content/uploads/2009/09/miniature-FM-transmitter.png"><img alt="miniature FM transmitter" class="alignleft size-full wp-image-2231" height="414" src="http://www.circuitstoday.com/wp-content/uploads/2009/09/miniature-FM-transmitter.png" title="miniature FM transmitter" width="585" /></a><br />
</strong></div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
</div>
<div style="text-align: justify;">
<strong>Notes.</strong></div>
<ul>
<li> Use a 3V battery for powering the circuit.</li>
<li>The circuit can be assembled on a Vero board.</li>
<li>Coil L1 can be made by making 5 turns of 24AWG wire on a 1cm plastic former.</li>
<li>Adjustments in the transmission frequency can be made by compressing or relaxing the coil.</li>
<li>Antenna can be  a 25cm long  18AWG wire.</li>
</ul>

Miniature FM transmitter

Description. This could be the simplest FM transmitter circuit you can find on the internet. Only using a single transistor and few passi...

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