pHATDAC/pifm mod - possible?


#1

I read somewhere in the depths of the webs that a DAC can be used to clean up a noisy radio signal… So - if this is the case, I am wondering if it’s possible to somehow mod pHATDAC to filter the ‘horrendously offensive and noisy’ digital output signal from pifm on (pin 7) and pipe out something a bit more friendly to other users of the airwaves.

PS - My lack of practical experience of modding electronics is surpassed only by my lack of theoretical experience. So try to keep any thoughts monkey-proof - looking forward to hearing anybody’s thoughts on the matter

Edit: The more I think about this the more I realise that it’s probably not possible without a whole shedload of hacks.


#2

I don’t believe it’s possible. The DAC expects a digital audio signal in, i2s in this case, and outputs an analog audio signal.

The output on pin 7 would, presumably, be analog audio? Or, rather, an specially modulated analog radio signal. I don’t expect the pHAT DAC would be able to do anything useful with it.


#3

Hey it’s the birthday boy himself - many happy returns!

Yes I believe the pin 7 output is very roughly modulated (digitally in fact - hence the problem with harmonics) audio…
It doesn’t surprise me that the DAC can’t be re-purposed in this way without major headaches… It would have been a cool aternative use of the DAC if it worked though. :) I think I need to learn how make my own basic filter as one of my first projects.

Thanks for taking the time between packing many Pi3s and partying to humour my wild idea :) Have a good one!

Edit: If anyone with an understanding of how FM radio and pifm works knows of a tutorial/kit for building a quality low pass/band-pass filter circuit, feel free to chime in.