I'm trying to control a DC (pager) motor with a sound signal so that I can use an audio synthesizer to control the speed of the motor. I'm hoping to modulate the speed of the motor at audio rate (1-200hz). I need to do a few things.
- Convert AC -> DC. A rectifier will chop the negative or fold it up, but how can I shift the waveform up, per se? What is the circuit equivalent of f(x)+1? (or will a rectifier be good enough)
- I could send the rectified signal straight to the motor, but this might be a waste of energy. Two strategies present themselves:
- Use a comparator to send only the peaks
- Use PWM (Frequency -> Pulsewidth)
Which do you think will work better? Can you think of other strategies? Should I implement this with, say, a small AVR chip, or with analog electronics?
An additional constraint is that the circuit has to be small. Ideally my motor + battery + circuit would be quarter-sized.
Any advice would be appreciated.
(I'll also need to do some lowpass filtering to avoid overwhelming the motors with information they can't respond to. Thoughts on this would be appreciated as well.)