This is part of a program I wrote a couple of years ago that
looks for a noise of a certain length in a quiet room. Wondered
why micro-sampling seemed to ring a distant bell. The PIC has
2*3-way DIP switches on it to set the sampling length and the
time-out before the next round of sampling. Basically the PIC
looks at the comparator under WDT timing and does a rough
majority test for the number of samples that are "1", just to
eliminate sounds that are too short. The signal level that will
cause a "1" at the output is set by a preset on the LP311's
input, ie no s/w filtering, it just has to be loud enough to flip the
comparator. The h/w is very similar to the pic I posted

tsmp = # of samples that are "1"
trp  = sampling period in WDT wake-ups
ipt  = input from comparator
gps1 = general purpose scratch
gps2 = general purpose scratch

;------ WAIT FOR TRIGGER

zzzz    sleep             ;low-power mode. Wait for WDT wake-up
        btfss  ipt        ;process if comparator active
        goto   zzzz       ;else back to sleep

        movf   trp,w      ;get trigger timing period reference
        btfsc  zero       ;if <> 0 then WDT required, start counting
        goto   out        ;else straight to output / timeout

;------ PROCESS TRIGGER AND COMPARATOR SIGNAL

        movwf  gps1       ;number of samples taken counter
        movf   tsmp,w
        movwf  gps2       ;results counter

sample  sleep             ;stay in this loop as long as needed
                          ;sampling every 192mS
        bcf    led        ;LED off by default
        btfsc  ipt        ;test comparator for LED
        bsf    led        ;LED on if comparator high

tcomp   btfsc  ipt        ;test comparator for compiling results
        decfsz gps2,f     ;decrease result ref value if sample = '1'
        goto   dtime      ;decrement timer
        goto   out        ;exit sampling loop if ref down to 0

dtime   decfsz gps1,f     ;decrement sample timer count
        goto   sample     ;continue if time left
        goto   entry      ;else start again

;------ OUTPUT

out     bcf    psu        ;front end power off
        bsf    opto       ;output on
        bsf    led        ;indicator on

etc

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