Appendix: Hacking


Do these at your own risk, hacker! You could very well break your POLY555!

Your POLY555 can be hacked! Here are some ideas:

  • You know the timers are tuned with their trimpots, but how can we make them a different octave? Try swapping their 4.7uF cap out to a higher value, maybe 10uF — higher values = lower frequency. You’ll probably want to play with the 100ohm resistor too; it sums with the trimpot and provides a “ceiling” that prevents you from tuning too high. Google the frequency formula for a 555 astable with 50/50 duty cycle for the math on how it all works.
  • If you have a switching audio jack, you could rig up an audio output that’s separate from the speaker. Good luck on mounting it inside the enclosure, though; there's not a ton of spare room!
  • Want more volume? The LM386 datasheet says it has a default gain of 20, but, if you put a 10uF electrolytic capacitor between pins 1 and 8 (with pin 1 the positive lead), you’ll get a gain of 200. Try other capacitor values too.