Vibration Motor Interface for Tactile Metronome

At the recent Maker Faire, we got a couple questions from people asking if the “tactile” part of the name meant that it 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.