Electronics Project Circuts

Single chip FM transmitter circuit

Sunil Jadhavar FM Transmitter Circuits 4:21 AM

<h3 style="text-align: justify;">
<strong>Description</strong></h3>
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<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>
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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>
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<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>
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Notes</h3>
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<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>
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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

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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>
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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>
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Circuit description.</h3>
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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>
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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

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<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

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<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>
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<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 />
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<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 />
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<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...

2 km FM transmitter

Sunil Jadhavar FM Transmitter Circuits 4:16 AM

<div style="text-align: justify;">
<strong>Description.</strong><br />
With a matching antenna, the FM transmitter circuit shown here can 
transmit signals up to a range of 2 kilo meters. The transistor Q1 and 
Q2 forms a classic high sensitive preamplifier stage. The audio signal 
to be transmitted is coupled to the base of Q1 through capacitor C2. R1,
 R3, R4, R6, R5 and R9 are the biasing resistors for the preamplifier 
stage comprising of Q1 and Q2. Transistor Q3 performs the collective job
 of oscillator, mixer and final power amplifier.C9 and L1 forms the tank
 circuit which is essential for creating oscillations. Inductor L2 
couples the FM signal to the antenna.<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/2009/12/2km-Fm-transmitter.png"><img alt="2km Fm transmitter" class="alignleft size-full wp-image-2720" height="273" src="http://www.circuitstoday.com/wp-content/uploads/2009/12/2km-Fm-transmitter.png" title="2km Fm transmitter" width="640" /></a><br />
<strong>Notes.</strong></div>
<ul>
<li> Assemble the circuit on a good quality PCB.</li>
<li>The circuit can be powered from anything between 9 to 24V DC.</li>
<li>Inductor L3 can be a VK220J type RFC.</li>
<li>For L1 make 3 turns of 1mm enamelled copper wire on a 10mm diameter 
plastic former. On the same core make 2 turns of 1 mm enamelled copper 
wire close to L1 and that will be L2.</li>
<li>Frequency can be adjusted by varying C9.</li>
<li>R9 can be used to adjust the gain.</li>
<li>For optimum performance, value of C8 must be also adjusted.</li>
<li>Using a battery for powering the circuit will reduce noise.</li>
</ul>
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2 km FM transmitter

Description. With a matching antenna, the FM transmitter circuit shown here can transmit signals up to a range of 2 kilo meters. The tran...

Long Range FM Transmitter

Sunil Jadhavar FM Transmitter Circuits 4:15 AM

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

<div style="text-align: justify;">
The use of transmitters which have a more powerful output than the ‘<strong>flea-power</strong>’
 are sometimes required when there are many obstacles in the path of 
the surveillance transmitter and monitoring station receiver, or 
the distance between them is too far so as to make a low powered 
device feasible. Whereas a typical micro transmitter will produce an 
RF power in the order of just a few milliwatts, i.e. a few thousandths 
of a watt, the VHF-FM transmitter described has a power output of 
between around a half and 2 watts, depending on the power source, which 
may be anywhere between 6 volts and 30 volts d.c. The battery or 
batteries should be of the alkaline high power type, since the current 
drain will be found to be relatively higher when compared to 
microtransmitter current drain. The power output of this device 
is somewhat proportional to the current drain and so therefore both may 
be decreased by altering the value of R6 to a higher resistance, or a 
variable resistor with a value of around 1k may be introduced in series 
with the existing R6, so as to give a variable power output. The <strong>variable resistor</strong>must
 not be a wirewound device because this would act as an inductor which 
will cause feedback problems.The audio input to the power oscillator, 
which incidentally is formed by TR2 and associated components, is 
derived from a piezoelectric microphone which drives the simple <strong>audio frequency amplifier</strong>
 TR1. The input of the audio amplifier is controlled by the gain pot R1,
 which selects the correct amount of voltage that is generated by the 
piezoelectric microphone, then connects this signal to the base of audio
 amplifier TR1 via C7. It may be found that there is insufficient 
housing space for a bulky piezoelectric microphone, so with a slight 
modification to the circuit, it is possible to employ an electret 
microphone insert as shown. Since the RF field that is generated by this
 transmitter is relatively large, the problem of RF feedback may very 
well be encountered. This may be overcome by placing the <strong>transmitter</strong> inside a metal enclosure, keeping all internal wiring as short as possible and the aerial wire.</div>
<h3 style="text-align: justify;">
<strong>Component listing for 1 watt transmitter</strong></h3>
<div style="text-align: justify;">
<strong>Resistors Semiconductors</strong> R1 = 27k TR1 = BC547 R2 = 330k TR2 = 2N2219 fitted with heat sink R3 = 5k6 MIC = piezoelectric microphone R4, 5 = 10k R6 = 100R</div>
<div style="text-align: justify;">
<strong>L</strong> = 6 turns 22 gauge enameled wire wound on 3⁄16″ former</div>
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<strong> Capacitors </strong></div>
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C1, 2, 3 = 330 pF C4 = 2–10 pF trimmer C5 = 4p7 C6 = 1 nF</div>
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C7,C8 = 40uF/25V Electrolytic</div>
<h3 style="text-align: justify;">
<strong>Circuit diagram for Long range FM Transmitter</strong></h3>
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<a href="http://www.circuitstoday.com/wp-content/uploads/2008/02/long-range-fm-transmitter.jpg"><img alt="Long range fm transmitter circuit" class="aligncenter size-full wp-image-5947" height="288" src="http://www.circuitstoday.com/wp-content/uploads/2008/02/long-range-fm-transmitter.jpg" title="long-range-fm-transmitter" width="640" /></a><strong>We have some other Radio Transmitter circuits of your interest;listed below:</strong></div>

Long Range FM Transmitter

Description The use of transmitters which have a more powerful output than the ‘ flea-power ’ are sometimes required when there are many...

PLL Stereo FM transmitter circuit

Sunil Jadhavar FM Transmitter Circuits 4:13 AM

<h3>
BH1417 IC</h3>
<div style="text-align: justify;">
The circuit shown here is of a good 
Stereo FM transmitter that can transmit high quality signals up to a 
range of 70 feet. The circuit is based on BH1417 PLL stereo transmitter 
IC from Rhom semiconductors. The IC has separate audio processing 
sections for the left and right channels, pre emphasis circuit for 
improving signal to noise ratio, crystal control circuitry for accurate 
frequency locking,  multiplex circuit for making sum ( left plus right) 
and difference ( left minus right)  {see this article for better 
understanding – Stereo decoder circuit}
 etc. Another important feature of this IC is that the transmission 
frequency can be set using a 4 channel DIP switch. The IC can be powered
 from anything between 4 to 6V DC and has an output power around 20mW. 
At full output power the circuit consumes only 20mA  and has a channel 
separation of 40dB.There are 14 possible preset transmission 
frequencies, starting from 88.7MHz and incrementing in steps of 0.2MHz 
that can be selected using the DIP switch. The PLL circuitry of the IC 
is so precise that there is practically no frequency drift.</div>
<h3>
Circuit diagram.</h3>
<div class="wp-caption aligncenter" id="attachment_6244" style="width: 1098px;">
<a href="http://www.circuitstoday.com/wp-content/uploads/2011/07/stereo-FM-transmitter-circuit.png"><img alt="BH1417 FM transmitter circuit" class="size-full wp-image-6244" height="379" src="http://www.circuitstoday.com/wp-content/uploads/2011/07/stereo-FM-transmitter-circuit.png" title="stereo FM transmitter circuit" width="640" /></a><div class="wp-caption-text">
Stereo FM transmitter circuit using BH1417</div>
</div>
<h3>
Circuit description.</h3>
<div style="text-align: justify;">
Capacitors C18 and C19 are DC decoupling
 capacitors for the left and right channel inputs. Capacitors C1 and C17
 are used to set the amount of pre-emphasis required and here with the 
used values it is 50uS. Capacitors C2 and C16 sets the roll-off point of
 the low pass filter. The crystal X1 is a 7.6MHz crystal which sets the 
oscillator’s frequency while capacitors C13 and C14 associated with are 
used for providing the appropriate loading. Resistors R8 to R11 are the 
pull-up resistors for the D0 to D3 (pins 15 to 18 of the IC) 
respectively. These pins can be held low by closing the corresponding 
switches. The RF oscillator of the IC is tuned using the components L1, 
C11, C12 and D1. Capacitor C11 prevents and DC voltage being applied to 
the varicap diode D1 and thereby prevents current flow into the inductor
 L1. More over it reduces the effects of changes in the capacitance of 
D1 on the pin 9. Capacitor C7 prevents any DC current from flowing into 
the inductor L1 from pin 9 of the IC. The composite output signal at pin
 5 is applied to the junction of R6 and R7 though a network comprising 
of components C4, C5, C6 and R1. In the circuit pin 19 of the circuit is
 left unconnected, but an optional capacitor at this pin can be used to 
set the pilot level and phase. Any way such a capacitor is not at all a 
necessity here and the circuit will work perfectly even if the capacitor
 at pin 9 is omitted.</div>
<div style="text-align: justify;">
The composite output signal undergoes 
some attenuation while passing through this network and finally reaches 
the varicap diode D1. The carrier frequency is controlled using the PLL 
(phase lock loop) phase detector output pin (pin 7) and the components 
connected around it. The darlington transistor Q1 is driven by the 
output of the pin7 and the transistor applies a control voltage on the 
varicap diode through resistor R5, R6 and R7. Capacitor C10 works as a 
high frequency filter while R7 is meant for isolation. Resistor R4 and 
capacitor C9 connected in series between the collector and base of Q1 
provides further filtering. Resistor R4 improves the response of the 
transistor to transient changes while capacitor C9 improves low 
frequency filtering. Capacitor C8 connected between collector and base 
of Q1 provides additional high frequency filtering. Resistor R3 serves 
as the collector load for the transistor Q1.</div>
<div style="text-align: justify;">
The modulated RF output is available at 
pin 11 and it is fed to the antenna through a filter network consisting 
of components L2, L3, C20, and C21. The job of this filter network is to
 remove harmonics. Resistors R12, R13 and R14 reduces the signal level 
to the antenna and as a result decreases the output power of the 
transmitter. Such a reduction is necessary to make the transmitter legal
 because in many countries transmitters that has an output power more 
than few milli watts (may change from nation to nation) are illegal. By 
omitting R12, R13, R14 and connecting the antenna directly to the 
junction of L2 and C21, the range can be increased, but do it at your 
own risk.</div>
<h3>
Setting up the transmitter.</h3>
<div style="text-align: justify;">
Firstly set the frequency of 
transmission using the DIP switch. Then connect the circuit to the power
 supply and connect the positive lead of your multimeter to pin 8 of the
 IC and the negative lead to ground. The multimeter should show a 
reading equal to the supply voltage. Now move the positive lead of the 
multimeter to the junction of R5 and R6 and adjust the slug (ferrite 
core of L1) so that the multimeter reads 2V. The L1 has to be readjusted
 for getting 2V between junction of R5, R6 and Ground every time you 
change the transmission frequency.</div>
<h3>
Notes.</h3>
<ul>
<li>Assemble the circuit on a good quality PCB.</li>
<li>The circuit can be powered from anything between 4 to 6V DC. I recommend using a 6V battery pack.</li>
<li>If you are using a battery eliminator for powering the circuit, it must be well regulated and free of any sort of noise.</li>
<li>Antenna can be a 1 metre long insulated copper wire.</li>
<li>Table for selecting the frequency is shown with the circuit diagram.</li>
<li>Crystal X1 is 7.68MHz.</li>
<li>For L1 make 2.5 turns of 1mm enamelled copper wire on a plastic former with an F29 ferrite slug inside it.</li>
<li>Optional 10K POTs can be connected in series to the input pins (pins 22 and 1) of the IC for adjusting the channel balance.</li>
<li>All electrolytic capacitors are rated at 10V DC.</li>
</ul>

PLL Stereo FM transmitter circuit

BH1417 IC The circuit shown here is of a good Stereo FM transmitter that can transmit high quality signals up to a range of 70 feet. Th...

Stereo FM transmitter circuit using BA1404

Sunil Jadhavar FM Transmitter Circuits 4:12 AM

<div style="text-align: justify;">
<strong>Notes.</strong><br />
A high quality stereo FM transmitter circuit is shown here. The circuit 
is based on the IC BA1404 from ROHM Semiconductors. BA1404 is a 
monolithic FM stereo modulator that has built in stereo modulator, FM 
modulator, RF amplifier circuitries. The FM modulator can be operated 
from 76 to 108MHz and power supply for the circuit can be anything 
between 1.25 to 3 volts.<br />
In the circuit R7, C16, C14 and R6, C15, C13 forms the pre-emphasis 
network for the right and left channels respectively. This is done for 
matching the frequency response of the FM transmitter with the FM 
receiver.  Inductor L1 and capacitor C5 is used to set the oscillator 
frequency. Network C9,C10, R4,R5 improves the channel separation. 38kHz 
crystal X1 is connected between pins 5 and 6 of the IC. Composite stereo
 signal is created by the stereo modulator circuit using the 38kHz 
quartz controlled frequency.<br />
<strong>Circuit diagram.</strong></div>
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<a href="http://www.circuitstoday.com/wp-content/uploads/2011/02/fm-transmitter.png" style="margin-left: 1em; margin-right: 1em;"><img alt="stereo fm transmitter" class="size-full wp-image-5075" height="345" src="http://www.circuitstoday.com/wp-content/uploads/2011/02/fm-transmitter.png" title="FM transmitter" width="640" /></a></div>
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Stereo FM transmitter circuit</div>
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<strong>Notes.</strong><br />

<ul>
<li> Assemble the circuit on a good quality PCB.</li>
<li>Powering the circuit from a battery will reduce noise.</li>
<li>Use an 80 cm copper wire as antenna.</li>
<li>For L1 make 3 turns of 0.5mm dia enamelled copper wire on a 5mm dia ferrite core.</li>
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Stereo FM transmitter circuit using BA1404

Notes. A high quality stereo FM transmitter circuit is shown here. The circuit is based on the IC BA1404 from ROHM Semiconductors. BA1404...

FM transmitter using UPC1651

Sunil Jadhavar FM Transmitter Circuits 4:10 AM

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<strong>Description.</strong><br />
Here is the circuit diagram of an FM transmitter using the IC UPC1651. 
UPC1651 is a wide band UHF Silicon MMIC amplifier. The IC has a broad 
frequency response to 1200MHz and power gain up to 19dB.The IC can be 
operated from 5V DC.<br />
The audio signals picked by the microphone are fed to the input pin 
(pin2) of the IC via capacitor C1. C1 acts as a noise filter. The 
modulated FM signal will be available at the output pin (pin4) of the 
IC. Inductor L1 and capacitor C3 forms the necessary LC circuit for 
creating the oscillations. Frequency of the transmitter can be varied by
 adjusting the capacitor C3.</div>
<strong>Circuit diagram with Parts list.</strong><br />

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

<ul>
<li> The circuit can be assembled on a Vero board.</li>
<li>Inductor L1 can be made by making 5 turns of 26SWG enameled copper wire on a 4mm diameter plastic former.</li>
<li>A ¾ meter insulated copper wire can be used as the antenna.</li>
<li>Do not give more than 6V to the IC.</li>
<li>Mic M1 can be a condenser microphone.</li>
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FM transmitter using UPC1651

Description. Here is the circuit diagram of an FM transmitter using the IC UPC1651. UPC1651 is a wide band UHF Silicon MMIC amplifier. Th...

200M FM Transmitter

Sunil Jadhavar FM Transmitter Circuits 4:04 AM

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<b>Description.</b><br />
A very stable and simple FM transmitter circuit is given here. With a 
matching antenna, this transmitter can attain a range of around 200 
meters. I assembled this transmitter few years and got very good 
results. Let us see how the circuit works.<br />
A condenser microphone (K1) is used to pick the sound to be transmitted.
 Capacitor C1 is a DC decoupler and the sound signal is coupled to the 
base of Q1 which wired as a preamplifier.R2 and R3 are the biasing 
resistors of Q1. Amplified sound signal will be available at the 
collector of Q1 and it coupled to the emitter of transistor Q2 through 
the capacitor C4 and 1mH inductor L1. Capacitor C4 decouples the DC 
component from the preamplifier output. Q2 performs the job of 
oscillator and modulator. Inductor L2 and variable capacitor C5 forms 
the tank circuit necessary for creating oscillations. Capacitor C6 is 
the feedback capacitor. The modulated FM wave will be available at the 
collector of Q1 and it is transmitted using the antenna A1.</div>
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<b>Circuit diagram.</b><br />
<a href="http://www.circuitstoday.com/wp-content/uploads/2010/01/200M-FM-transmitter-circuit.png"><img alt="200M FM transmitter circuit" class="alignleft size-full wp-image-2877" height="379" src="http://www.circuitstoday.com/wp-content/uploads/2010/01/200M-FM-transmitter-circuit.png" title="200M FM transmitter circuit" width="633" /></a><br />
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<b>Notes.</b><br />
<ul>
<li> Assembling the circuit on a good PCB will give better results.</li>
<li>I used a 12V battery for powering the circuit. A 9V PP3 battery will also do the job.</li>
<li>A battery eliminator is also fine but it will induce noise.</li>
<li>Antenna A1 can be a 25cm long copper wire.</li>
<li>K1 is a condenser microphone.</li>
<li>C2 should be a Tantalum capacitor.</li>
<li>Variable capacitor C5 can be used to adjust the transmission frequency.</li>
<li>This simplified formula will help you in making inductors<b>, L = (d²n²) / (18d+40l)</b>. Where <b>L</b> is the inductance of the coil in uH , <b>d</b> is the coil diameter in inches, <b>l</b> is the coil length in inches and <b>n</b>
 is the number of turns. Just try to make the inductor your self using 
this formaula. If you can’t, then comment here.I will give you the 
winding details.</li>
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200M FM Transmitter

Description. A very stable and simple FM transmitter circuit is given here. With a matching antenna, this transmitter can attain a range ...

Simple FM transmitter circuit.

Sunil Jadhavar FM Transmitter Circuits 4:02 AM

Simple FM transmitter circuit.

Two transistor FM transmitter. Description.

PWM motor speed controller

Sunil Jadhavar 7:49 AM

PWM motor speed controller

Description. This circuit is designed as per a request made by Mr Vinoth from India. His requirement was a 12V/5A DC fan motor controller...

Wireless mains voltage tester.

Sunil Jadhavar 7:46 AM

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<b>Description</b>.<br />
This circuit can be used to test whether mains voltage is <span class="IL_AD" id="IL_AD6">present</span>
 or not without having electric contact with mains line. The CMOS IC 
CD4033 is the heart of this circuit. The CD4033 consists of a 5 stage 
decade Johnson counter and an output decoder for converting the Johnson 
code to a 7 segment decoded output for driving 7 segment <span class="IL_AD" id="IL_AD4">LED display</span>. A 10cm long insulated <span class="IL_AD" id="IL_AD2">copper wire</span> connected to the clock pin (pin1) of <span class="IL_AD" id="IL_AD5">the IC</span>
 serves as the sensor. The sensor wire has to be placed in the vicinity 
of the mains wire to be tested. When there is no voltage in the mains 
line, no voltage will be induced in the sensor wire and the display will
 show a random digit. When there is voltage in the mains line, a small 
voltage will be induced in the sensor wire due to electromagnetic 
induction and this voltage is sufficient enough to clock the CMOS IC 
CD4033. Now the display will count from zero to nine and repeat.<br />
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<b>Circuit diagram.</b></div>
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<a href="http://wiringdiagramcircuit.com/images/19/2009/09/wireless-mains-indicator1.png"><img alt="wireless mains indicator" height="295" src="http://wiringdiagramcircuit.com/images/19/2009/09/wireless-mains-indicator1.png" title="wireless mains indicator" width="400" /></a><br />
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<b>Notes.</b></div>
<ul>
<li> The circuit can be assembled on a Vero board.</li>
<li>Use 9V PP3 battery for powering the circuit.</li>
<li>Use a 10cm insulated wire as the sensor.</li>
<li>The IC must be mounted on a holder.</li>
<li>Switch S1 can be a miniature ON/<span class="IL_AD" id="IL_AD3">OFF switch</span>.</li>
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Wireless mains voltage tester.

Description . This circuit can be used to test whether mains voltage is present or not without having electric contact with mains line....