In Reply to: Re: Musical instrument tuners (sound frequency comparison) posted by Andrew Freer on 09/08/00 at 5:10 PM:
Okay, now that it's decided that you'll address only the tempered scale, your project can move ahead.
I suggest that you consider Linear Technology's switched-capacitor filters. One possibility is the LTC1064 which can be seen at: http://www.linear-tech.com/cgi-bin/parser?action=pdf&var=lt1064.pdf
You would choose a mode of operation and configure the chip as directed. Then the bandpass center frequency will be controlled by your choice of clock frequency, said clock frequency being some multiple of the bandpass center frequency.
With an appropriate microhone and audio preamplifier at the input of the filter and an appropriate AC voltmeter circuit on the output of the filter, playing an instrument nearby and adjusting that instrument's tuning up and down from the bandpass center frequency will cause the voltmeter reading to peak when the instrument's note is in tune.
John Dunn - President