I plan to use small headphone speakers as a vibration units. The idea is to supply them from my Panda 2 digital pins through some circuit that will oscillate at low frequency. Yes, I’m aware that there are variety of coin v motors, but I want to use this approach. What kind of oscillator circuit do I need to build? Does anyone have some schematics to suggest?
What about using Pwm?
All pwms are already used for different things. Also I would need to control 10 to 12 speakers and I only have 6 pwm pins on Panda II.
True but with OutputCompare any DIO can become a PWM 
Will simulating 10 pwms consume too much of processor time?
Depending on the frequency.
I would need low frequencies, I suppose about 100-200 Hz.
So that is 400 interrupts per second. 10 signals = 4000 per second. It should work but maybe you need less outputs.
Only up to four of them will be active at the same time.
If it’s not too late! you could try using 5 or 6, 556 dual timer ic’s but then you would also need 10 or 12 digital pins.