For this project, my team member and I had to design and create an electrical circuit. We decided to go with a FM Transmitter that used a variable capacitor. This project was for an Engineering class in Spring 2009. The picture below is the end product. We were able to connect an iPod to our circuit and broadcast the song over the air to a radio.
Unfortunately, our circuit schematic has long gone and vanished. The dog probably ate it…
To explain the circuit with words, we used a tank circuit which is a variable capacitor and inductor in parallel. This is what broadcasts the sound at a certain frequency. By changing the capacitance, the tank circuit will resonate at a different frequency. The circuit we constructed was extremely sensitive as the capacitor’s range was too wide. One small twitch and you would lose the sound on the radio. We noticed that for our circuit, since it was so poorly constructed, could only play on the radio when the station was only static. If a station already was already a radio station, then we would never have any luck.
When we first started out with just a tank circuit, we could barely hear anything, so to make things
better, we added an amplifier to the circuit. Our final circuit was pretty much an amplifier connected to
our tank circuit with a poorly made antenna.
We were actually able to broadcast sound to the radio, but like I previously said, it would only work on stations that were pure static. We had to make sure there was no noise around otherwise our circuit would not work. Our circuit usually had to be fairly close to the radio to actually hear anything. Compared to our goals, we were able to play sound to a radio in the frequencies we were expecting. Unfortunately, that was all we were able to do. For our very first circuit I think we accomplished a lot.