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| Hardware Frequency detector (for audio) |
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| RJSV:
Hello again; I've hit the barrier, too high IC count. This project is not directly intended for stage-ready performance, (or even always in tune!). It is possible to build a couple channels for tests, the audio device will 'correct' an incoming frequency, say 289 hz corrected to 293 hz. There is no explicit phase 'tracking' on a fine basis, as seen in PLL circuits. However, there is a quick response, not needing dozens of cycles to produce a result. At 220hz, even one cycle will take 5 milliseconds to get first result. And the device could make a heck of a 'drop out' corrector, basically running a pulse stream ouput 'forever'. The channel status signal 'Signal Present' flags the on-off sounding times. Channel outputs can have more than one frequency, producing one or two octaves higher, (limited cases), and easily producing one or two octaves lower (than middle C) Thats similtaneous frequencys in one channel, each with an audio sine gen. For ease of audio handling, advantage is taken, of a mass of OP-amps. Each capacitor connects to a differential subtractor OP-amp stage, which then connects to compare with the 'current' best detected value. That result is where the input analog section ends, and the 'front-end' digital result is. There is consequently no shifting or excess commutation of the analog sample. There is, however, the piper to pay, for the digital access to that 'result' flag is horrendous, involving a sequential barrel bit shifting scheme. Doing this layout for more than a couple channels is just too much, tho, something like 120 OP-amp stages for 6 channels!!! The Modulo counter RESET is an awesome and simple method, for synchronizing, when called for. Also, along the lines of sync input, it is possible to 'deaden' any phase test contest for the last clock state, before T0. That way a slight wavering of the phase will not cause the results to cycle rapidly ( a sort of hysterisis). I'd like to point the machine at itself, running same freq. outputs, as in theory it should detect (its own output). And of course there are many issues of detection width, errors, etc. Thanks. |
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