A short range FM transmitter is a low-power FM radio transmitter that broadcasts a signal from a portable audio device (such as an MP3 player) to a standard FM radio. Most of these transmitters plug into the device's headphone jack and then broadcast the signal over an FM broadcast band frequency, so that it can be picked up by any nearby radio. This allows portable audio devices to make use of the louder or better sound quality of a home audio system or car stereo without requiring a wired connection. Being low-powered, most transmitters typically have a short range of 100–300 feet (30–100 meters), depending on the quality of the receiver, obstructions and elevation. Typically they broadcast on any FM frequency from 87.5 to 108.0 MHz in most of the world . In this project we design the circuit in such a way that ,the circuit will collect the input through aux cable and broadcast with in FM frequency range. The broadcasted output can be collected with a FM radio.
Now I am going to instruct how to make a FM Transmitter with less number of components.
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Lets Get Started..
Step 1: Components Required
2N3904 - 2 [ Banggood ]
Resistors [ Banggood ]
100k Ω - 1
100Ω - 1
1M Ω - 1
1k Ω - 1
10k Ω - 3
0.1µH inductor (Air coil)
Capacitors [ Banggood ]
0.1µF - 2
40 pf trimmer - 1
4.7 pF - 1
10pF - 1
9V battery and clip [ Banggood ]
PCB [ Banggood ]
Step 2: Circuiting
I attached the pcb layout , you can directly use this , to etch the pcb.
Fritzing file of circuit is attached.
Once the pcb is prepared, insert the components in to pcb according too circuit and solder it.
Now we need to make Inductor, Take a copper wire of 18 gauge or 22 gauge.
For 18 Gauge wire, form a inductor with 4-5 turns of 1/4 inch (or)
For 22 Gauge wire, form a inductor with 8-10 turns of 1/4 inch.
Now solder the Inductor to the circuit,
If you have antenna, solder it or take hook up wire of 8-10cm as antenna.
I used 3.5mm female audio jack , because we can frequently plugin mic,audio devices easily.
If you uses mic ,it senses the audio and broadcast to near by fm radio. It can also be used as spy bug.
Step 3: Making PCB
In this , I used permanent marker as protective coat for pcb.
Step 4: Tuning Transmitter
Now the time to tune the transmitter, which is very hard and time taken process. Be patience while tuning.
By varying the trimmer capacitor ,you can vary the transmission frequency.
Slowly vary the trimmer capacitor, then at a point you can hear some distortion in radio.
Then slowly vary in that area, when transmitter and receiver frequency matches you can get the clear output from radio.
By tuning the frequency , making of FM transmitter is completed.
For detailed construction check the video below.