April 2013Electronics Project Circuts

Make a Simple Non-Contact AC Mains Voltage Detector

Sunil Jadhavar 6:23 AM

<div class="bh_teaser" data-bhtrackregion="ArticleTeaser">
Fault 
finding in complicated mains wirings often becomes a hard nut to crack 
for every electrician involved in the business. The simple circuit idea 
presented here can surely help them to get rid of headaches accompanied 
during such tedious assignments.</div>
<h3>
Introduction</h3>
The
 simple non-contact AC voltage detector, sensor, tester circuit design 
presented in this article will be especially useful to all those 
electrical engineers and electricians who are engaged in difficult 
electrical circuit designing, repairing and fault finding jobs. A fault 
inside any AC electrical system is basically caused through a break in 
the continuity of specific wires and may result in a major breakdown of 
the whole system. These breaks in the wires are generally caused by 
aging, short circuits, or in some places rats could be the main cause of
 these malfunctions. 
Our domestic AC mains (house wiring) voltage
 is made up of alternating currents that keep shifting phase from 
positive half cycle to negative half cycle. This happens very fast, 
normally 50 to 60 times per second. Due to this rapid alteration in its 
phase, alternating currents generate a fair bit of electrical 
disturbance in the air. 
The proposed circuit is actually a very 
sensitive radio frequency detector and is able to pick even the 
slightest of electrical disturbance that may be present in the area 
surrounding it. It is also able to detect the presence of the mains AC 
voltage from quite a fair distance. Therefore, to find a break inside 
electrical wiring, the unit’s antenna may be just dragged across the 
whole length of the suspected wiring. The circuit will just stop, 
indicating the presence of an AC phase exactly at the point where the 
break may have occurred, and thus is able to pinpoint the exact place of
 the cut in the wiring. 
<ul class="jcarousel-skin-tango" id="bh_sections">
<li><div>
<div class="bh_section bh_sectionString" data-bhtrackregion="ArticleSection">
<h3>
How does the Circuit Function?</h3>
 
By
 referring to the circuit schematic we can see that the whole circuit is
 wired around the IC 324, which is a package of 4 op-amps or quad 
op-amps. 
It forms the heart of the circuit. One of its op amps, 
A1, is configured as a high gain current to the voltage converter and 
the second one, A2, is used as a buffer to produce a stabilized output 
on detection of an AC signal. 
(Click Image to Enlarge) 
<a href="http://img.bhs4.com/92/a/92acd9822ab487933d235dcb03308b8cee8d92a9_large.jpg" style="width: 100%;" title="Non Contact AC Mains Voltage Sensor, Circuit Diagram, Image"><img alt="Non Contact AC Mains Voltage Sensor, Circuit Diagram, Image" src="http://img.bhs4.com/92/a/92acd9822ab487933d235dcb03308b8cee8d92a9_small.jpg" /> </a>The
 moment the antenna of the circuit is taken near a conductor carrying 
AC, the vibrations around the conductor are immediately picked up. These
 tiny alternating vibrations induce a corresponding current ripple into 
the circuit, disturbing the overall stability of the circuit. 
 
These
 input disturbances are instantly amplified by A1 and converted into an 
output voltage equal to the peak supply voltage of the circuit. The out 
put is fed to the next amplifier stage via capacitor C1. 
On 
receiving the pulse, A2 further amplifies the signal to produce a visual
 indication, showing the presence of an AC phase, and vice versa. 
The value of R2 may be increased or decreased to correspondingly increase or decrease the sensitivity of the circuit.</div>
</div>
</li>
<li><div>
<div class="bh_section bh_sectionString" data-bhtrackregion="ArticleSection">
<h3>
Parts List</h3>
The
 following parts may be procured from your local electronic spare part 
retailer. Just hand over this list to him and he will know exactly what 
requirements you have and provide you with the items on the list: 
All resistors are 1/4 watt, 5%, CFR, unless otherwise specified. 
R1 = 100 K, 
R2
 = 10M (means 10 Mega Ohms - 1Mega Ohms is equal to 1000Kilo Ohms and 
1Kilo Ohms is equal to 1000 Ohms. Ohm is the basic unit of measurement 
for resistors. 
 
R3 = 470 Ω, 
C1 = 0.01microFarad, CERAMIC, DISC 
A1, A2 = IC 324, 
BATTERY 9V PP3, 
GENERAL PCB, 
PLASTIC ENCLOSURE</div>
</div>
</li>
<li><div>
<div class="bh_section bh_sectionString" data-bhtrackregion="ArticleSection">
<h3>
Construction Clues</h3>
 
The
 circuit of this non-contact AC voltage detector can be easily built 
within a small piece of general PCB with the help of the given circuit 
schematic. Just insert all the procured components into the PCB, bend 
their leads to interconnect, and solder the relevant points. The whole 
assembly, along with a 9 Volt battery, may then be enclosed inside a 
small plastic container with only its antenna protruding out of the box.
 The antenna may be any conductor 3 inches in length, fixed externally 
to the box and connected internally to the circuit. 
 
 
 
(Click Image to Enlarge)<a href="http://img.bhs4.com/82/7/8274197ed1d32056b334f5e2c507c0517df93e6a_large.jpg" style="width: 100%;" title="AC Mains Signal Detector, Prototype Image"><img alt="AC Mains Signal Detector, Prototype Image" src="http://img.bhs4.com/82/7/8274197ed1d32056b334f5e2c507c0517df93e6a_small.jpg" /> </a> 
 
While testing, do not let any of your body part touch the antenna of the unit, as that will produce a false indication. 
The unit is now ready and may be used to trace out the AC voltage interruptions within the wiring in question.</div>
</div>
</li>
</ul>

Make a Simple Non-Contact AC Mains Voltage Detector

Fault finding in complicated mains wirings often becomes a hard nut to crack for every electrician involved in the business. The simple c...

Flashing LED

Sunil Jadhavar LED Projects 7:39 PM

The
 circuit is designed to use very little current to prolong battery life 
so that it can be left on permanently. A superbright’ red LED is used 
because this provides a bright flash with a low current.

If
 you want to use 4.5V supply by connecting 3 Alkaline cells or any other
 source, change the resistor along with LED from 3.3k to 1k for a better
 flash.

Note that AA cells will last longer than a 9V PP3 battery <img alt=";)" class="wp-smiley" src="http://rookieelectronics.com/wp-includes/images/smilies/icon_wink.gif" />

To flash two LEDs alternatively we have to increase the clock pulse speed to possibly fastest to have exact proper alternation.

Parts Required:

<ol>
<li>100k potentiometer</li>
<li>10k and 3.3k</li>
<li>10mF</li>
<li>LED</li>
<li>555 Timer</li>
<li>9v Battery</li>
</ol>
<div>
 
</div>
Circuit Diagram:

<div>
There are three different modes to flash an LED using 555 Timer</div>
<img alt="" class="alignnone wp-image-88" height="143" src="http://rookieelectronics.com/wp-content/uploads/2012/07/Flashing-LED-300x227.jpg" title="Flashing LED1" width="189" /><img alt="" class="alignnone wp-image-83" height="150" src="http://rookieelectronics.com/wp-content/uploads/2012/07/Flashing-LED2-300x227.jpg" title="Flashing LED2" width="200" /><img alt="" class="alignnone wp-image-84" height="143" src="http://rookieelectronics.com/wp-content/uploads/2012/07/Flashing-LED3-300x227.jpg" title="Flashing LED3" width="189" />

and their bread board arrangements

Flashing LED

The circuit is designed to use very little current to prolong battery life so that it can be left on permanently. A superbright’ red LED i...

Capacitor uF - nF - pF Conversion Chart

Sunil Jadhavar 7:32 PM

When reading schematics, repairing radios and buying capacitors, you often must convert between uF, nF and pF. 
Paper and electrolytic capacitors are usually expressed in terms of uF (microfarads). Short forms for micro farad include 
uF, mfd, MFD, MF and UF. Mica capacitors are usually expressed in terms of pF (micromicrofarads) (picofarads). 
Short forms for micromicrofarads include pF, mmfd, MMFD, MMF, uuF and PF. A pF is one-millionth of a uF. In between a pF and
a uF is a nF which is one-one thousands of a uF. Converting back and forth between uF, nF and pF can be confusing with
all those darn decimal points to worry about. Below is a uF - nF- pF conversion chart. Just print a copy and tape it
to your workbench....it will come in handy. Have fun with your radio restorations. 
 
<img alt="high_voltage_electrolytic_capacitors" height="90" src="http://justradios.com/filtercap.jpg" width="100" />
<img alt="axial_tubular_capacitors" height="75" src="http://justradios.com/axial.gif" width="120" />
<img alt="orangedip_capacitors" height="91" src="http://justradios.com/orangedips.gif" width="86" />
<img alt="axial_electrolytics" height="80" src="http://justradios.com/axialEcap.gif" width="80" />
<img alt="high_voltage_disc_capacitors" height="70" src="http://justradios.com/disccapacitors.jpg" width="100" />

Capacitor Shopping Cart 
Capacitor Excel OrderForm 
Capacitor $ Price List 
Capacitor KITS

To use this table, just read across. For example, 1uF is same 1,000nF or 1,000,000pF.

Capacitor uF - nF - pF Conversion Chart

When reading schematics, repairing radios and buying capacitors, you often must convert between uF, nF and pF. Paper and electrolytic capac...

Cellphone-Based Remote Controller for Water Pump

Sunil Jadhavar Mobile Starter for Water Pump 8:33 AM

<h5>
<img align="right" border="" height="90" src="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_pictures/8E7_Logo.jpg" width="100" /></h5>
Design By Sunil 
<hr />
<div align="justify">
Inconvenience
 in switching on a water pump installed in a remote farm is a common 
problem faced by farmers. Many circuits have been developed to solve 
this problem. Most of them are expensive and microcontroller-based. Here
 we present a cellphone-based remote controller for water pump. By 
calling the cellphone attached to the controller, the water pump can be 
directly activated. 
 Circuit and working Fig. 1 shows 
the block diagram of cellphone-based remote controller for water pump. 
Fig. 2 shows the circuit. The circuit is built around DTMF decoder IC 
MT8870 (IC1), timer NE555 (IC2) wired as monostable multivibrator and a 
few discrete components. The main component of the circuit is IC MT8870.
 This DTMF decoder has band-split filter and digital decoder functions. 
It offers the advantages of small size, low power consumption and high 
performance. <table align="center" border="0" cellpadding="3" cellspacing="3" style="width: 100pixelspx;"><tbody>
<tr><td><img border="" height="114" hspace="3" src="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_pictures/77Z_1.jpg" vspace="3" width="400" /> 
Fig. 1: Block diagram of cellphone-based remote controller for water pump </td></tr>
</tbody></table>
 <table align="center" border="0" cellpadding="3" cellspacing="3" style="width: 100pixelspx;"><tbody>
<tr><td><img border="" height="175" hspace="3" src="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_pictures/4D7_2.jpg" vspace="3" width="400" /> Fig. 2: Circuit of cellphone-based remote controller for water pump </td></tr>
</tbody></table>
 
Once
 monostable timer IC2 is triggered, its output goes high for the preset 
time period. The time period depends on the values of resistor R7 and 
capacitor C4. It can be adjusted between 8 and 50 minutes using 
pot-meter VR1. The high output at pin 3 of IC2 energises relay RL1 to 
switch on the water pump. The triggering pulse for IC2 is 
generated by DTMF decoder IC1 and the arrangement of diodes D1 through 
D5. Std pin of IC1 provides a high pulse when a valid tone-pair is 
received. Transistor T1 conducts only when outputs Q0 through Q2 and Std
 are high simultaneously. This can be achieved by sending digit ‘7’ 
through DTMF.<table align="center" border="0" cellpadding="3" cellspacing="3" style="width: 100pixelspx;"><tbody>
<tr><td><img border="" height="171" hspace="3" src="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_pictures/EB8_test-points.jpg" vspace="3" width="300" /></td></tr>
</tbody></table>
 <table align="center" border="0" cellpadding="3" cellspacing="3" style="width: 100pixelspx;"><tbody>
<tr><td><img border="" height="444" hspace="3" src="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_pictures/D7C_parts-list.jpg" vspace="3" width="300" /></td></tr>
</tbody></table>
The
 water pump controller is connected to a dedicated cellphone through 
connector J1 with auto-answering mode enabled. The DTMF signal sent from
 the user end is decoded by the DTMF decoder and the corresponding 
binary-coded decimal (BCD) value appears on outputs Q0 through Q3. In 
this circuit only three of them are used. Working of the circuit 
is simple. To switch ‘on’ the water pump, call the cellphone connected 
to the controller circuit and press ‘7’ once the ring stops. LED1 will 
glow to indicate that the water pump is switched on. The water pump 
turns off automatically after the preset time. LED1 turns off 
simultaneously. Construction and testing An 
actual-size, single-side PCB for cell-phone-based remote controller is 
shown in Fig. 3 and its component layout in Fig. 4. Suitable connector 
is provided on the PCB to connect the cellphone. Assemble the circuit on
 a PCB to minimise time and assembly errors. Carefully assemble the 
components and double-check for any overlooked error. Use suitable IC 
socket for MT887 and NE555 ICs.<table align="center" border="0" cellpadding="3" cellspacing="3" style="width: 100pixelspx;"><tbody>
<tr><td><img border="" height="364" hspace="3" src="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_pictures/92E_3.jpg" vspace="3" width="450" /> <a href="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_files/A86_Fig-3-water-pump.pdf" target="_blank">Fig. 3: An actual-size, single-side PCB for cellphone-based remote controller</a> </td></tr>
</tbody></table>
 <table align="center" border="0" cellpadding="3" cellspacing="3" style="width: 100pixelspx;"><tbody>
<tr><td><img border="" height="364" hspace="3" src="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_pictures/48C_4.jpg" vspace="3" width="450" /> <a href="http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_files/19C_Fig-4-waterpump.pdf" target="_blank">Fig. 4: Component layout for the PCB</a></td></tr>
</tbody></table>
Use relay RL1 with contact current rating capable of carrying the water pump’s current. To
 test the circuit for proper functioning, press switch S1 and verify 5V 
at TP1 with respect to TP0. Connect the cellphone to the controller 
using connector J1. Call this cellphone and press ‘7’ once the ring 
stops. At the same time, verify high-to-low triggering pulse at TP2. TP3
 now should be high for the preset time period. 
<hr />
The
 author is a final year B.Tech (electrical and electronics engineering) 
student at MG University. His areas of interest include embedded systems
 and power electronics</div>

Cellphone-Based Remote Controller for Water Pump

Des ign By Sunil Inconvenience in switching on a water pump installed in a remote farm is a common problem faced by farmers. Many cir...

Automatic Bike Headlight Switch

Sunil Jadhavar 8:32 AM

<div id="content" itemprop="articleBody">
 Improved bike headlight switch circuit presented here has been 
designed to switch bike headlight on (or similar loads) at a 
presettable ambient light level. The circuit is based on the renowned 
timer chip LM555 (IC1), here triggered by a decrement in ambient light 
level. Here is a 220V automatic light switch, just in case you need one.
how does the automatic headlight switch works?
 
When 12VDC supply is applied to the circuit, the voltage at pin 2 of 
IC1 is set by the voltage divider built around the Light Dependent 
Resistor (LDR) and trimpot P1 (100K). If the ambient light level 
(presetted by P1) is sufficient, pin 2 of IC1 is at a high potential and
 as a result IC1 is disabled. Capacitor C1 (100uF/25V) added across the 
LDR eliminates possible unwanted circuit functioning which may caused by
 sudden fluctuations in the light level.
 

However, when ambient light level drops, the resistance of LDR 
increases and the voltage level at pin 2 of IC1 drops to trigger the 
monostable circuit. Simultaneously, the base of transistor T1 (BC557) is
 pulled low and discharges the timing capacitor C3 (100uF/25V). Next, 
output (pin 3) of IC1 goes high to turn on the electromagnetic relay 
(12V/SPDT). The RC time constants (R1 and C3) sets this on time for a 
period of near 5 seconds. But if the light level stays low, T1 holds C3
 in the discharged state and the relay stay on. Common (C) and 
Normally-Opened (N/O) contacts of the relay can be used to switch the 
headlight. 

The timeout of five seconds is introduced deliberately to avoid 
erratic switching of the headlight due to other strong light 
reflections. This also allows the headlight to stay on for a finite time
 after the ambient light level restoration.

<h2>
Automatic Light Switch Circuit Schematic</h2>
<a href="http://electroschematics.com/wp-content/uploads/2013/02/Automatic-Bike-Headlight-Switch.jpg" title="Automatic Light Switch Circuit Schematic"><img alt="Automatic Bike Headlight Switch Schematic" class="alignnone size-large wp-image-8465" height="305" src="http://electroschematics.com/wp-content/uploads/2013/02/Automatic-Bike-Headlight-Switch-550x305.jpg" width="550" /></a>

Bike Headlight Switch Notes

<ul>
<li>The whole circuit should be powered from the 12V bike battery</li>
<li>Slight intervention in the existing electrical wiring of the vehicle may become necessary to add this circuit</li>
<li>Use of a medium-size encased LDR is recommended for reliable 
operation. Fit the LDR at the front side of the bike in an appropriate 
position</li>
<li>The relay used in the prototype draws near 37.5 mA. 555 IC output 
can switch up to 100mA, which is adequate for driving the relay</li>
<li>555 IC will only rise to near 10v for the 12V input supply and the 
diode D1 will drop 0.7Volt. As a result the 12V relay will only get 
about 9.3Volt. However, pick-up voltage of a standard 12V relay is 9V, 
this is not a problem. D1 is added intentionally to avoid episodic timer
 latch up</li>
</ul>
<div class="info">
<a href="http://electroschematics.com/650/lm555-datasheet/" title="555 datasheet">555 datasheet</a></div>
<div class="bottomads">
 
 <ins style="border: none; display: inline-table; height: 250px; margin: 0; padding: 0; position: relative; visibility: visible; width: 300px;"><ins id="aswift_1_anchor" style="border: none; display: block; height: 250px; margin: 0; padding: 0; position: relative; visibility: visible; width: 300px;"></ins></ins>
 </div>
</div>

Automatic Bike Headlight Switch

Improved bike headlight switch circuit presented here has been designed to switch bike headlight on (or similar loads) at a preset...

Light Activated Relay with 555 IC

Sunil Jadhavar 8:29 AM

This light activated relay circuit presented here uses the 555 timer 
IC and a light dependent resistor or LDR to form a light sensitive relay
 in an intruder alarm system or for switching on a lamp at Sun set and 
off at Sun rise.
Potentiometer R1 value must be chosen and then adjusted that under 
normal conditions when the light is falling on the LDR the voltage 
across the LDR is less than 1/3 of Vcc. The output of the 555 IC is high
 now. The actual value of R1 will depend on the resistance of the LDR.
 
When the light fades or is interrupted by an intruder, the voltage 
across it rises above 2/3 of Vcc, tripping the IC flip-flop. The output 
goes low activating the relay. When the light is restored, voltage falls
 below 1/3 of Vcc, again tripping the flip-flop causing the output to go
 high and the relay drops. 

The difference of 1/3 of Vcc between turning on and turning off 
voltages prevents relay chatter. This differential can be reduced by 
connecting a resistor R2 shown dotted in the schematic. Its value is 
about one and a half times of the LDR resistance in its illuminated 
condition. Use a 6V or 12V relay with a current of 200mA max.

<h2>
Light Activated Relay Circuit Schematic</h2>
<a href="http://electroschematics.com/wp-content/uploads/2013/03/light-activated-relay.jpg" title="Light Activated Relay Circuit Schematic"><img alt="light activated relay circuit schematic" class="alignnone size-full wp-image-8510" height="376" src="http://electroschematics.com/wp-content/uploads/2013/03/light-activated-relay.jpg" width="521" /></a>

<div class="info">
<a href="http://electroschematics.com/650/lm555-datasheet/" title="555 datasheet">555 datasheet</a></div>

Light Activated Relay with 555 IC

This light activated relay circuit presented here uses the 555 timer IC and a light dependent resistor or LDR to form a light sensitive rel...

Lead-Acid Battery Charger Circuit

Sunil Jadhavar 8:27 AM

This circuit delivers an initial voltage of 2.5V per cell to rapidly 
charge a car battery. The charging current decreases as the battery 
charges and when the current drops to 180 mA the charging circuit 
reduces the output voltage to 2.35 V per cell, leaving the battery in a 
fully charged state. This lower voltage prevents the battery from 
overcharching, which will shorten its life. 
 
The LM301A compares the voltage drop across R1 with a 18 mV reference
 set by R2. The comparator’s output controls the voltage regulator, and 
produce the lower float voltage when the battery-charging current, 
passing through R1, drops bellow 180 mA. 

Temperature compensation helps prevent overcharging, the LM334 
temperature sensor should be placed near or on the battery. Because 
batteries need more compensation at lower temperatures, change R5 to 30Ω
 for a tc of -5mV/0C per cell il this circuit will be used at 
temperatures below – 200C. 

The charger’s input voltage must be filtered dc that is at least 3V 
higher than the maximum required output voltage. Choose a regulator for 
the maximum current needed: LM371 for 2A, LM350 for 4A, LM338 for 8A. At
 250C and with no load, adjust R7 for a Vout of 7.05V, and adjust R8 for
 a Vout of 14.1V.

<h2>
Car battery charger circuit diagram 
</h2>
<h2>
<a href="http://electroschematics.com/wp-content/uploads/2009/11/lead-acid-battery-charger.gif" target="_blank"><img alt="lead acid battery charger" class="alignnone size-large wp-image-7091" height="330" src="http://electroschematics.com/wp-content/uploads/2009/11/lead-acid-battery-charger-550x330.gif" title="" width="550" /></a></h2>

Lead-Acid Battery Charger Circuit

This circuit delivers an initial voltage of 2.5V per cell to rapidly charge a car battery. The charging current decreases as the battery c...

13.8V 20A power supply

Sunil Jadhavar 8:24 AM

<img border="0" height="365" src="http://www.electronics-lab.com/projects/power/002/schem_th.gif" width="550" /> 
<div align="left" class="MsoNormal" style="text-autospace: none;">
 
 This 
 PSU has been especially designed for current-hungry ham 
 radio transceivers. It delivers safely around 20Amps at 
 13.8V. For lower currents, a separate current limiting 
 output, capable of 15ma up to a total of 20A has been 
 added. Let us see what we have got here. The power 
 transformer should be capable to deliver at least 25A at 
 17.5 to 20V. The lower the voltage, the lower power 
 dissipation. The rectified current will be “ironed” by the 
 C1, whose capacity should not be less than 40.000uF, (a 
 golden rule of around 2000uF/A), but we recommend up to 
 50.000uF. This capacity can be built up by
 
 
 several smaller capacitors in parallel. The base of this 
 design is a simple 12V regulator (7812). The output voltage 
 can be brought to desired value (here 13.8V) by two 
 external resistors (R5 and R6) using this formula: 
 </div>
<div align="left" class="MsoNormal">
 
 U= 
 12(1+R5/R6) 
 </div>
<div align="left" class="MsoNormal">
 
 The 
 low currents (here 15mA) will keep the 7812 in its regular 
 function. As soon as the current rises over 15ma, the 
 voltage drop on R4 will “open” the Q3, actually handling 
 the high output current. This is a PNP transistor (Ic>25) 
 and current amplification factor of at least 20. The one 
 that has been tested and proven here is the 2N5683. The 
 current limiting resistance RL, for the maximum output of 
 20 Amps should be 0.03 Ohms, rated at
 
 </div>
<div align="left" class="MsoNormal">
 
 least 
 15W. You can use the resistance wire or switch several 
 resistors in parallel, totaling the resistance/power 
 values. Values for other currents can be calculated by the 
 rule: 
 </div>
<div align="left" class="MsoNormal">
 
 RL=0.7/Imax</div>
<div align="left" class="MsoNormal">

 
  The 
 RL and Q2 (3A PNP such as BD330) form a short circuit 
 “automatic fuse”. As soon as the maximum current reaches 
 20Amps, the voltage drop over the resistor RL will open Q2, 
 and thus limit the B-E Current of Q3. Parallel to Q2 is Q1, 
 which lights the LED 1 whenever the current limiting 
 circuit is active. When the “fuse” is active, the Q2 
 bridges the R3, so the full current would flow through the 
 IC1, and damage it. Therefore the R4 is inserted, as to 
 limit the IC1 current to 15mA. This makes it possible to 
 run the IC1 without any cooling aid. The LED 2 will light 
 up every time the PSU is switched on.
 
 </div>
<div align="left" class="MsoNormal">
 
 There 
 is an adjustable current limiter in parallel to the fixed 
 output, thus providing adjustable current source for 
 smaller currents. 
 </div>
<div align="left" class="MsoNormal">
 
 This 
 circuit is very simple too. You will notice that there is 
 no current sensing resistor. But it is really there, in a 
 form of the Rds-on resistance of the N-channel FET, which 
 actually handles the load cutoff from the source. The 
 function of the FET is shown in the diagram 2. When the 
 current Id is rising, the tension Uds over the resistance 
 Rds rises very slowly in the beginning, but very fast after 
 the knick. This means, that before the knick the FET 
 behaves as a resistor but after it, works as constant 
 current source. 
 </div>
<div align="left" class="MsoNormal">
 
 The 
 D2, R3 and B-E connection of the Q4 will sense the Uds 
 voltage of the FET1. When the voltage rises enough, the Q4 
 will shortcut the FET1 gate to mass, and cut the current 
 flow through the FET 1 off. However, to enable the FET1 to 
 open, there is certain gate voltage necessary, which in 
 this case is brought up by the voltage divider consisting 
 of R8, Z1, P1 and R9. So the maximum Gate voltage will be 
 the one of the Z1, and the minimal will be around 3V6. The 
 Z1 voltage (Uz1) will thus determine the max current 
 flowing through the FET 1.
 
 </div>
<div align="left" class="MsoNormal">
 
 The 
 diagram 2 will show that for 5 Amps the Uz1 should be 5V6, 
 and for 20Amps around 9V6. The Capacitor C4 will determine 
 the “velocity” or the reaction time of the limiter. 100 uF 
 will make the reaction time to be around 100ms, and 1n will 
 make it 1us. 
 </div>
<div align="left" class="MsoNormal">
 
 Within the designed limits, the P1 will limit the current 
 output in the range of 15mA to 20A. You can use both output 
 simultaneously, but the total output current will be 
 limited by the value of the RL. This PSU can be built also 
 for higher outputs, as long as the transformer will handle 
 the current requirements, and you provide sufficient 
 cooling for the Q3. 
 </div>
<div align="left" class="MsoNormal">
 
 If 
 somebody will be interested, there is a PCB design ready.
 
 </div>
<div align="left" class="MsoNormal" style="text-autospace: none;">

 
 Have 
 fun. 
 </div>
<div align="left" class="MsoNormal" style="text-autospace: none;">
 
 
 </div>
<div class="MsoNormal" style="text-autospace: none;">
 
 <img border="0" height="325" src="http://www.electronics-lab.com/projects/power/002/pcb.gif" width="524" /></div>
<div class="MsoNormal" style="text-autospace: none;">
 
 <img border="0" height="441" src="http://www.electronics-lab.com/projects/power/002/layout.gif" width="623" /></div>
<div align="left" class="MsoNormal" style="text-autospace: none;">
 
 REV1. 
 </div>
<div align="left" class="MsoNormal">
 
 I 
 have received several requests for some modifications, and 
 the one I find useful is the addition of an amp meter. 
 Therefore the slightly modified diagram is included in this 
 revision. All elements within the dotted border are now 
 placed on the pcb. There is also elements placement design 
 included. Should one have an 25Amp instrument on hand, 
 there is nothing easier. Just mount it in line and there it 
 goes. However, a ham would probably find an instrument 
 somewhere in his “junk-box”, but the scale would be 
 something completely different, let say an “S” or 
 Voltmeter. No problem. We already have a “shunt” for the 
 amp-meter, and it is there as the Current limiting resistor 
 “RL”. As 
 
 already known from before, there is a voltage drop of 0V7 
 over the resistor at current flow of 20A. What we now have 
 to do, is to simply measure the voltage drop over the 
 resistor, and co-relate it with the current. Let us say 
 that our instrument has an internal resistance of 13R, and 
 has a full scale reading of 60mV. The voltage drop over the 
 RL is 0V7 for 20Amps. Therefore, we need another resistance 
 in line with the instrument, that would bring the 0V7 to 
 60mV, or an voltage drop of 640mV. 
 </div>
<div align="left" class="MsoNormal">
 
 The 
 formula is simple: 
 </div>
<div align="left" class="MsoNormal">
 
 U1:R1=U2:R2
 
 </div>
<div align="left" class="MsoNormal">
 
 60:13=640:X
 
 </div>
<div align="left" class="MsoNormal">
 
 X=13x640/60
 
 </div>
<div align="left" class="MsoNormal">
 
 X=138.66 
 </div>
<div align="left" class="MsoNormal">
 
 Therefore, the resistance that has to be inserted in line 
 is around 140R. I suggest to insert a trimmer (VR1) of 
 around 200R, to fine trim the reading when calibrating the 
 instrument. Using your favorite drawing software, design 
 your scale to your likings, (at least 20A for the full 
 scale) and insert it in the instrument you have. Due to the 
 many requests for the PCB Layout, I have included the 
 design here. The exact dimensions of
 the 
 pcb are 160x100mm. Please remember, that the pcb has to be 
 printed as a mirror image, to obtain higher quality when 
 transferring it to the copper side of the board.
 
 </div>

 
 Wish 
 you a good time.

13.8V 20A power supply

This PSU has been especially designed for current-hungry ham ...

IC Pinouts

Sunil Jadhavar 8:19 AM

IC Pinouts

Electronics Circuit Symbols

Sunil Jadhavar 8:16 AM

Electronics Circuit Symbols

Color Codes for Resistors

Sunil Jadhavar 8:10 AM

<div class="separator" style="clear: both; text-align: center;">
<img alt="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/1R0-Resistor.gif" class="decoded" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/1R0-Resistor.gif" /> </div>
<div class="separator" style="clear: both; text-align: center;">
If 
 3rd band 
 is gold,
 Divide by 10 
 If 3rd band is silver, Divide by 100 
 (to
 get 0.22ohms etc)</div>
 
<table border="0" cellpadding="0" cellspacing="0" id="table284" style="width: 100%px;"><tbody>
<tr><td></td>
 <td> </td>
 </tr>
<tr>
 <td colspan="2">
 <img border="0" height="480" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/E24ResistorColorCodes-1.gif" width="640" /></td></tr>
</tbody></table>

Color Codes for Resistors

If 3rd band is gold, Divide by 10 If 3rd band is silver, Divide by 100 (to get 0.22ohms etc) ...

Constant Current Drives Two 3 WATT LEDs

Sunil Jadhavar 8:07 AM

<img border="0" height="335" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/ConstantCurrent5wLEDs.gif" width="355" /> 
 This constant current circuit 
 is designed to drive two 3-watt Luxeon LEDs. The LEDs require 
 1,000mA (1Amp) and have a characteristic voltage-drop across them of 
 about 3.8v. Approximately 4v is dropped across the LM317T regulator 
 and 1.25v across the current-limiting resistors, so the input 
 voltage (supply) has to be 12.85v. A 12v battery generally delivers 
 12.6v.
 
 The LM 317T 3-terminal regulator will need to be heatsinked. 
 This circuit is designed for the LM series of regulator as they have 
 a voltage differential of 1.25v between "adj" and "out" terminals.

Constant Current Drives Two 3 WATT LEDs

This constant current circuit is designed to drive two 3-watt Luxeon LEDs. The LEDs require 1,000mA (1Amp) and have a charac...

1-WATT LED - very good design

Sunil Jadhavar LED Projects 8:03 AM

<table border="0" id="table307" style="width: 668px;"><tbody>
<tr><td width="310"><div align="center">
 
 <img border="0" height="290" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/1wattLED.gif" width="325" /> 
 Circuit takes 70mA on LOW brightness 
 and 120mA on HIGH Brightness</div>
</td>
 <td>
 This circuit has been specially designed 
 for a 6v rechargeable battery or 5 x 1.2v NiCad cells. Do not use 
 any other voltage. 
 It has many features: 
 The pulse-operation to the two 1-watt LEDs delivers a high current for a short 
 period of time and this improves the brightness. 
 The circuit can drive two 1-watt LEDs with extremely good brightness 
 and this makes it more efficient than any other design. 
 The circuit is a two-transistor high-frequency oscillator and it 
 works like this: 
 The BD139 is turned ON via the base, through the white LED and two 
 signal diodes and it amplifies this current to appear though the 
 collector-emitter circuit. This current flows though the 1-watt LED to turn 
 it ON and also through the 30-turn winding of the inductor. At the 
 same time the current through the 10R creates a voltage-drop and 
 when this voltage rises to 0.65v, the BC547 transistor starts to 
 turn ON. This robs the base of the BD139 of "turn-on voltage" and the 
 current through the inductor ceases to be expanding flux, but 
 stationary flux. </td>
 </tr>
</tbody></table>
The 1n capacitor was initially pushing 
 against the voltage-rise on the base of the BC547 but it now has a 
 reverse-effect of allowing the BC547 to turn ON. 
 This turns off the BD139 a little more 
 and the current through the inductor reduces. 
 This creates a collapsing flux that produces a voltage across the 
 coil in the opposite direction. This voltage passes via the 1n 
 to turn the BC547 ON and the BD139 is fully turned OFF. 
 The inductor effectively becomes a miniature battery with negative 
 on the lower LED and positive at the anode of the Ultra Fast diode. The 
 voltage produced by the inductor flows through the UF diode and both 
 1-watt LEDs to give them a spike of high current. The circuit 
 operates at approx 500kHz and this will depend on the inductance of 
 the inductor. 
 The circuit has about 85% efficiency due to the absence of a 
 current-limiting resistor, and 
 shuts off at 4v, thus preventing deep-discharge of the 
 rechargeable cells or 6v battery. 
 The clever part of the circuit is the white LED and two diodes. 
 These form a zener reference to turn the circuit off at 4v. The 10k 
 resistor helps too. 
 The circuit takes 70mA on low brightness and 120mA on HIGH brightness via the brightness-switch. 
 The LEDs actually get 200mA pulses of current and this produces the 
 high brightness.

1-WATT LED - very good design

Circuit takes 70mA on LOW brightness and 120mA on HIGH Brightness This circuit has been specially design...

10 LED Chaser

Sunil Jadhavar LED Projects 8:01 AM

10 LED Chaser

Here's an interesting circuit that creates a clock pulse for a 4017 from a flashing LED. The flashing LED takes almost no curre...

Solar Garden Light

Sunil Jadhavar 7:59 AM

Solar Garden Light

This is the circuit in a $2.00 Solar Garden Light. The circuit illuminates a white LED from a 1.2v rechargeable cell.

Police Lights

Sunil Jadhavar 7:57 AM

Police Lights

These three circuits flash the left LEDs 3 times then the right LEDs 3 times, then repeats. The only difference is the choice of chi...

Bike Turning Signal

Sunil Jadhavar 7:56 AM

This circuit 
 can be used to 
 indicate left and right turn on a motor-bike. Two identical circuits 
 will be needed, one for left and one for right. 

 <img border="0" height="145" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/bikeLeftAnim.gif" width="128" />                                   
 <img border="0" height="145" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/bikeRightAnim.gif" width="128" /> 
 <img border="0" height="345" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/bikeLeftCct.gif" width="475" />

Bike Turning Signal

This circuit can be used to indicate left and right turn on a motor-bike. Two identical circuits will be needed, one for left an...

4 Way Traffic Lights

Sunil Jadhavar IC555 Project, LED Projects 7:54 AM

4 Way Traffic Lights

This circuit produces traffic lights for a "4-way" intersection. The seemingly complex wiring to illuminate the light...

Traffic Lights

Sunil Jadhavar IC555 Project, LED Projects 7:50 AM

Here's a clever circuit using two 555's to produce a set of traffic 
 lights for a model layout. 
 The animation shows the lighting sequence and this follows the Australian-standard. 
 The red LED has an equal on-off period and when it is off, the first 
 555 delivers power to the second 555. This illuminates the Green LED 
 and then the second 555 changes state to turn off the Green LED and 
 turn on the Orange LED for a short period of time before the first 
 555 changes state to turn off the second 555 and turn on the red 
 LED. A supply voltage of 9v to 12v is needed because the second 555 
 receives a supply of about 2v less than rail. This circuit also 
 shows how to connect LEDs high and low to a 555 and also turn off 
 the 555 by controlling the supply to pin 8.  Connecting the 
 LEDs high and low to pin 3 will not work and since pin 7 is in phase 
 with pin 3, it can be used to advantage in this design.  
 <table border="0" id="table215" style="width: 483px;">
 <tbody>
<tr>
 <td width="63"><img border="0" height="178" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/TrafficLight.gif" width="38" /></td>
 <td><img border="0" height="240" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/TrafficLights-1.gif" width="385" /></td></tr>
</tbody></table>

Traffic Lights

Here's a clever circuit using two 555's to produce a set of traffic lights for a model layout. The animation shows the light...

Flashing Railroad Lights

Sunil Jadhavar IC555 Project, LED Projects 7:27 AM

Flashing Railroad Lights

This circuit flashes two red LEDs for a model railway crossing.

The Resistor

Sunil Jadhavar 7:20 AM

The value of the current limiting resistor can be worked out by Ohms 
 Law. 
 Here are the 3 steps: 
 1. Add up the voltages of all the LEDs in a string.   e.g:  
 2.1v + 2.3v + 2.3v + 1.7v = 8.4v 
 2. Subtract the LED voltages from the supply voltage.  e.g:  
 12v - 8.4v = 3.6v 
 3. Divide the 3.6v (or your voltage) by the current through the string. 
 
 for 25mA:   3.6/.025 =144 ohms 
 for 20mA:   3.6/.02  = 180 ohms 
 for 15mA:   3.6/.015 = 250 ohms 
 for 10mA:   3.6/.01   = 360 ohms 
 This is the value of the current-limiting resistor.
 
 
 Here is a set of strings for a supply voltage of 3v to 12v and 
 a single LED: 
 <img border="0" height="620" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/Strings-2.gif" width="550" /> 
   
Here is a set of strings for a 
 supply voltage of 5v to 12v and a white LED:
 <img border="0" height="470" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/Strings-WhiteLED.gif" width="550" />
 Here is a set of strings for a 
 supply voltage of 5v to 12v and two LEDs: 
 <img border="0" height="470" src="http://www.talkingelectronics.com/projects/30%20LED%20Projects/images/Strings-2LEDs.gif" width="550" />

The Resistor

The value of the current limiting resistor can be worked out by Ohms Law. Here are the 3 steps: 1. Add up the voltages of all the L...

Electronics Project Circuts