FM Stereo Transmitter

Reader [Mike Y] responded to our “What are you working on?” post  with his stereo FM transmitter project. If you’ve ever used an FM transmitter for your portable audio, you know that even the best consumer level ones can be difficult to make sound decent.

He obtained an NS73M FM Transmitter module from Niigata Seimitsu Company, but it required a controller to handle pre-emphasis, modulation level, frequency, and power level. He decided on an Arduino which would also control his LCD.

His results were quite good, with decent range and superb audio quality. His total cost thus far is $35, but he still needs to put it in an enclosure. You can find complete schematics as well as source code and helpful tips on his site.  You may also want to check out the regulations on broadcasting(pdf) as well.

20 thoughts on “FM Stereo Transmitter

  1. Looks like a great project, but he states that it compares favorably in cost to the Ramsey kit that sells for $45. His costs $35 (15 for FM module, 15 for arduino, and 5 for LCD module), not $80.

  2. This is a very nice project for arduino users, because it combines several important aspects into a real product:
    – LCD
    – Saving settings across reset
    – Encoder (nice!)
    – Talking with another device

    Examples of using each of these pieces can be found in various places on the net, but this is a good example of tying them all together with a concrete example.

  3. Thanks. Wow, I made Hackaday…

    Yes, no new ideas here; just integrating a bunch of things I’ve learned from others out there.

    There are two versions of code (.PDE) there. The original uses up and down switches, plus an off/on-air toggle. The most recent version is compatible with the latest Arduino 0012, and uses a single rotary encoder for change frequency and toggle on-air. Photos of the finished item in an enclosure hopefully this week.

  4. Hey Mike Y:

    Can you use the rotary encoder from an old PC mouse?

    I have one tied to a VCR head to make a huge aluminium knob :)

    Would it be possible to use an Atmega8 16PU ? that is what I have on hand.

    What kind of range do you get from 2mw?

  5. > Can you use the rotary encoder from an old PC mouse?

    I’m sure; I’ve tried constructing one of these for a ham project, but it’s too dang difficult to get everything lined up. But, you get the same quadrature signal as a mechanical encoder (without the bouncing signals!). I need to do an EagleCad schematic for this, as I’ve added 74HC14 and an RC debounce circuit for the cheap, $1.70 Bourns encoder. Works fine.

    Would it be possible to use an Atmega8 16PU / 3.3V ?

    Heck yes, and no translation from 5V to 3V I2C signals. On the breadboard, I used just a resistor pullup to 3.3v, but in the final version, I’m using a SparkFun 5V to 3.3V board.
    If you don’t need the LCD, I think you could get by with 2 pins (I2C), so an ATTINY85 might do; just re-flash it to change the frequency.

    What kind of range do you get from 2mw?

    I can go about 65 feet with it. After that – pretty sharp drop-off. Drive is with about 60% volume on an iPod nano, no input amplification needed. I was going to add compression/limiting, but that’d probably be ‘gilding the lily’.

    Mike Y
    Dallas, Texas

  6. ok, i want to make something like this with the least amount of supplies and the least sophisticated parts. while making a strong signal that might break the fcc’s signal strength rule, but stay within their distance regulations, does anyone think this is possible?

  7. ||philly||, did you get something about your question?

    I would like to know about a high power FM transmitter. It would be nice to be able to hear my ipod in my car, but commercial FM transmitters don’t have enought power…

    Anyone has any clue about this?

  8. In any gadgets with music I prefer using the ones with fm transmitters, because it is always good to hear brand new hit musics not only from the ones you have downloaded but also you will not be bored to hear the same thing again shuffling from your gadgets.

  9. Hello author, It’s going to be really great help for me. I want to develop FM Transmitter for my home with micro controller interfacing. My aim is to listen fm from my mobile which will given by the ns73m fm transmitter module. Before I go for that, I would like to clarify few things like, 1. How much distance It can transmit the signal with clear cut audio.? 2. Will it give pure audio in fm or with disturbance.? For getting audio, Should I go for another circuit implementation or no need.? Thanks in advance.

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