piclist 2000\05\27\014855a >
Thread: Audio Ideas?
face BY : Josh Koffman email (remove spam text)

"M. Adam Davis" wrote:
> This is something I've been meaning to make.  But it will still be a month or
> two before I get to it, so...
> You have 1 analog input, and run the chip at 20MHz.  Use a fast fourier
> transform to get the level in 10 different frequency bands, and drive a 10x10
> matrix of LEDs.  One could do an 8x8 or 16x16 or just about any size spectrum
> analyzer out of such a setup.  A 16f876 would have the right number of I/O to do
> 10x10 with one audio input and an extra i/o pin.  It may not be too much to ask
> for to have it drive two 8x8 displays with two audio inputs.

Something like that (2 inputs, 8x8 display) sounds really interesting. I
imagine the coding for this would be pretty hard though. This is
probably a bit out of my league.

> At any rate, there have been several threads on FFT on a PIC in the past, look
> at http://www.piclist.com/ for the archive and search for FFT.
> You should probably start out doing a reguler VU meter first, then do a
> peak-holding VU meter, then decide whether a spectrum analyzer is worth it or
> feasable.  By then the 18Fxxx chips will be common with their 8x8 multiply to
> speed your fft up quite a bit.

Right now all I really want is the VU meter. Do you think it is even
feasible to do an 8 input, 8 bar graph out VU meter in a 16f877? Do you
have any pointers as to how to even begin? I checked the archive, and I
still am not sure how to process the input on adc to provide a proper
output on the display. If I can only get one output per pic, it would
probably be easier to use a dedicated linear chip. I only want to use
the pic for the coolness factor, plus a reduced parts count, and
eventually I can interface it with a computer.

Josh Koffman

<392F5EA7.FC1E2F75@mb.sympatico.ca> 7bit

See also: www.piclist.com/techref/microchip/ios.htm?key=audio
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