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Based on circuit from Electronotes #87, by Bernie Hutchins. I had an eight channel version of this module in my original OGEE synth. I decided four channels would be enough to produce randomness with undetectible patterns. The circuitry shown for channels A and B in the schematics are repeated for channels C and D in U4 and U5 (see PCB). The module produces a sort of PWM effect on sloped waveforms (saw, triangle). Since there are four different modulation frequencies under 1Hz, the sound is much richer than PWM. It's also very interesting to look at on a scope. Design equations
Waveform Animator schematic A Waveform Animator 2x PCB layout Those goofy orange traces on the PCB layout should be wires - I laid out this circuit with the power supply connections backwards on the LM339 (V+ should be pin 3 and V- pin 12). Since it was wrong on my schematic (the corrected version is shown here), it missed all my checks until I plugged the chips in. Needless to say, it did not pass the smoke test! |
