Building a 20x20 matrix with vibrator motor coins

Question

I am currently doing a project that requires a 20x20 matrix with coin type vibrator motors.

I am not sure how to pull this off. What is the best way of driving all the motors all together? Provided that I will be applying different PWM frequencies to all of them at the same time.

I am going to be using a motor that requires 60 mA at 3 V:

10x Nuevo DC 3 V 60mA 9000 +/-2000 RPM de la Moneda Del Teléfono Plana Motor de Vibración Que Vibra (10x New 60mA DC 3V +/- 2000 RPM 9000 Coin Vibration Motor Phone Plana vibrating).

Answer 1

400 motors at 60mA per motor is a total of 24A maximum supply current. If you multiplex the motors then peak current will be much higher and could become impractical, so it will probably be best to drive them independently.

To apply different PWM frequencies to each motor, every one will need its own switching circuit (MOSFET, flyback diode, bulk capacitor). It's only a small step from there to providing each motor with its own MCU, all of which can be networked together and controlled from a single point.

Depending on the physical arrangement of the motors, it might be better to combine several motor drivers on a single pcb, or just make 400 individual boards and arrange them however you wish. Each board could have an input connector and a pass-through connector, so they can easily be daisy chained in rows or columns without extra wiring. This is similar to how 'intelligent' LED light strips work.

400 individual circuits might sound like an expensive way to do it, but with bulk purchasing it should work out to only a few dollars per board (less if you get them manufactured in China!).

Answer 2

I believe you don't need multiple PWM frequencies but wether independent pulse widths or just independent frequencies.

Single PWM frecuency (Independent puse widths)

I don't know if this motors will behave as LEDs. If the motor produces several forces depending on the width then this is what you might want.

You would need a single sawtooth oscilator, as much as 400 comparators (maybe many FPGAs), many analog references (FPGAs could be handy) and many analog multiplexers.

^{simulate this circuit – Schematic created using CircuitLab}

Independent frequencies

If every motor works at independent frequencies, would you also need to modulate width? Maybe, if you want to have 3D feedback. If you want to modulate frequency only, then you need also a single frequency source (the maximmum frequency) you can obtain lower frequencies by means of a frequency divider. 4 bit programmable dividers will provide 16 different frequencies. The downside is that you need as much as 400 dividers (maybe a FPGAs could help here as well.)

^{simulate this circuit}