I was looking to have a wireless stage audio monitor and I was researching how can I be able to do that with less cost. Then suddenly I realize that most of the cellphones today have FM radio built-in so why just take advantage of it? The idea is simple, connect a FM transmitter to the audio mixer and use your phone’s FM radio to listen to the sound from the mixer. tadaaaa! you have an instant simple wireless monitor!
I searched for local store who offers fm transmitter and I got 3 options from alexan, deeco and e-gizmo. The FM transmitter from deeco is just a simple 1 stage transistor FM transmitter which is not reliable. The frequency drift with voltage, so if you are using a battery, you will have a frequency drift overtime. It has also short range so I decided not to use it. While the FM transmitter of alexan is good but they have some missing parts so I didn’t bought it. Now the only choice is from e-gizmo, looking at the design, it is best among the 3. It has a display where you can see what frequency it is transmitting.
Schematic
it uses a chip AS6001 FM transmitter which is control by a microcontroller for changing the frequency.
Power supply design
One crucial part of the design is to have a clean power supply. Without designing a clean power supply, you will experience a lot of humming which is not pleasant to ears. I already have a post on how to design a clean power supply for audio applications. Read here: https://tataylino.com/clean-power-supply-for-audio-application/
The image above shows the power supply I designed for the FM transmitter.