Single transistor DIY FM transmitter with an enclosure.

Description

Transmission range: 5-30 meters.

This is yet another basic FM Transmitter using one transistor. We have previously made another single transistor FM transmitter also. This is a learning kit for electronics beginners and hobbyists who want to learn about FM transmission as well as soldering. Basic soldering is enough to build this transmitter. It should take about half an hour to make a perfectly working FM transmitter. The silkscreen labels printed on the PCB should be enough to guide you through soldering.

It works as an FM bug also. The box has enough space to fit in 2 pieces of AAA size batteries.

Schematic:

Features:

1. Transmission range: 5m-30m (depending upon antenna length, test environment, power supply, and FM receiver )
2. Voice transmission: You can only transmit voice using this FM transmitter. Audio transmission, for example, audio from your phone or any other audio sources is not possible.
3. First test: You can test the transmitter immediately after you assemble it. You can use any general FM radio. You should hear a feedback noise when your transmitted signal matches with the reception frequency.
4. Frequency range: 88Mhz-108Mhz. Tune your FM radio until you hear a noise.
5. You cannot adjust the frequency. If your transmitter is transmitting at 88.9Mhz and there is also a commercial FM transmitting at the same frequency, your transmission will overlap the commercial broadcast. When you go away from the transmitter (more than 30 meters), the commercial broadcast will again take its frequency. If you want a transmitter with variable frequency, then this is the right transmitter(long-range transmitter) for you.
6. Antenna: if you use 20cm wire as an antenna, it can transmit up to 30m. With 10-20cm, it can transmit up to 10 meters.
7. Operating voltage: 2.4V. We have tested separately using a 5V adapter and the transmission was great.
8. PCB Size: 49*13mm
9. Bx Size: 55*35*15mm
10. Receiver devices: General FM radio/cellphone which has FM radio function/Car FM radio(Recommended for testing)

Components included in the package:

1. 1 x PCB
2. 1 x antenna wire
3. 1 x set of enclosure
4. 1 x switch and its red cap
5. 1 x 5T inductor
6. 1 x Electret microphone
7. 1 x 47uF capacitor
8. 1 x 200 Ohm resistor
9. 1 x 10K resistor
10. 1 x 47K resistor
11. 2 x 0.1uF (code: 104)
12. 2 x 15pF
13. 1 x  20pF
14. 1 x 47pF
15. 1 x 0.01uF (code: 103)

What do you need to arrange yourself?

1. 2 x AAA size batteries
2. Any FM radio with a telescopic antenna.

Not working? This is how you troubleshoot.

1. Look at the back of the PCB, make sure there is no short.
2. The electret microphone polarity could be wrong.
3. The battery connector could be connected incorrectly. Make sure that you didn’t connect the positive terminal of the battery to the negative and vice versa.
4. Resistors soldered incorrectly.
5. Check the polarity of the capacitor.

How to test ?

After assembling the transmitter completely, turn it on and turn on your FM receiver and tune the radio until you hear a feedback noise. If you hear the feedback noise, the transmitter is working. Place the transmitter on a table, play music from your phone, take your receiver, and go away from the transmitter. You will keep on hearing the music on your FM receiver up to 30 meters.