In this article you are going to see how to make fm transmitter. A short range fm transmitter is low power portable fm transmitter which can be make with less number of components . The actual frequency of fm is 88MHz to 108MHz . This bandwidth is subjected to law of respective countries . It is illegal to use the bandwidth without the permission of government . This a simple project made for educational purpose . This fm transmitter can be capable to transmit up to 50-100 meters .
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 ]
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.
Making PCB :
Download PCB files : Download
Transmitter Tuning :
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.
Circuiting and Testing : Watch Video