Variable Pitch Beeper

	     ATtiny45
	      --v--
    rst pb5 -|     |- vcc
     pi pb3 -|     |- pb2 sck keyin
     po pb4 -|     |- pb1 miso tone1
	gnd -|     |- pb0 mosi tone0
	      -----	
	      8Mhz

Uses BynaseDriver

Simple software io is not fast enough to make pure tones that vary smoothly so we press the timer/counter into service.

This program generates an audio tone by toggling oc1a at a frequency determined by pi. The tone is keyed by keyin which is active low.

             ATtiny45
              --v--
    rst pb5 -|     |- vcc
     pi pb3 -|     |- pb2 sck keyin    -- /|
     po pb4 -|     |- pb1 miso oc1a ---||< |
        gnd -|     |- pb0 mosi         -- \|
              -----        
               8Mhz

Here is code that computes compare-register values to play musical notes. Change $n=12 to, say, 256, and you get close to continuous variation.

  perl -e '$n = 12; for $i (0..$n) {
    $p = 2.0**($i/$n); 
    $f = 440*$p;
    $t = int(256/$p+.5);
    $g = 8e6/((2**6)*$t);
    $e = 100*($g-$f)/$f;
    print "$i\t$f\t$t\t$g\t$e\n"}'