Vibration Motor Interface for Tap-Tempo Metronome

At the recent Maker Faire, we got a couple questions from people asking if the metronome buzzed or vibrated. While that’s not part of the standard kit, we decided to try it out, by adding a vibration motor:

We used a very similar technique as for the drum solenoid interface, but the vibration motor didn’t require a transistor, and could be driven directly from the microcontroller.

With this circuit, we connect the driving pulse output pin through a 30 ohm resistor to the positive terminal of the motor. The negative terminal of the motor is connected to ground. Just like the solenoid, a motor is a coil of wire, which can create dangerous inductive kickback when we turn off the output pin. To protect our circuitry from this kickback, we added a protection diode just like with the solenoid circuit.

In the firmware code for the microcontroller, we had to make each output pulse last a bit longer, since the vibration motor needs a longer pulse to get up to full speed. We found that pulse lengths longer than 100 ms worked well. Perhaps we could use shorter pulses if we added a transistor instead of driving the motor directly.

The circuit above was inspired by the most excellent LilyPad Vibe Board.