FM Data Receiver Module for Micro-controllers

There are an incredibly large number of TX and RX Modules for micro-controllers. The cheapest I found was $9.99, not bad but I remember seeing FM receivers at the dollar store. Plus it uses a RDA5807SS with I²C for tuning.(not that its to difficult to use but you must know the instruction set.) It also was not for digital transmission to the micro-controller, just spit out audio.

With an Op Amp and a few components a cheap FM digital receiver can be made.

• $1 FM receiver
• Dual Comparator (LM2903)
• Switching Diode (1N4148)
• Potentiometer (22k)
• 150pF Cap
• 10kΩ resistor
• 4.7kΩ resistor
• 4 pin header

Step 1 The Circuit

   It is basically an envelope detector on the non-inverting and a variable voltage on the inverting input on the first comparator. Then the output is buffered and inverted by the second comparator. It is simple but took some development. I tried op amps and Schmitt triggers, but they let too much noise though, or did not have the power necessary to drive logic. An envelope to Schmitt works great, but it would require a step up transformer. (too big for my liking, and 13 grams)