I'm having issues with the Ardumoto shield. I want to use a motor at 5V with a 12V 2A power supply connected to the Arduino board.

From my understanding, the ardumoto shield gets its power directly from the Vin pin. How am I supposed to reduce the voltage for the motor? Also, should I worry about the big amperage coming in from the power supply?

Thank you for your help.

  • \$\begingroup\$ I'm thinking about using two small resistors to make a voltage divider. Would it work? \$\endgroup\$
    – Hilydrow
    Commented Feb 21, 2012 at 7:18
  • \$\begingroup\$ No, It would not. \$\endgroup\$ Commented Feb 21, 2012 at 10:45

1 Answer 1


Your best bet is to drive the tiny motor directly with a darlington transistor like the BC517 and 5V, or make 6V and drive it off that. The motor shield is simply overkill for this. Just make sure you dont stall it - the shortcut current in this setup might be to high. Do not forget to add a flyback diode antiparallel with the motor in this setup.

You might put a resistor in series with the motor.

A voltage divider in front of the motor will not work, because the lower part of it is parallel to the shield or motor.

  • \$\begingroup\$ To reduce the voltage in half I would need a resistance as big as the motor, correct? How can I determine the resistance of the motor? \$\endgroup\$
    – Hilydrow
    Commented Feb 21, 2012 at 17:12
  • \$\begingroup\$ No. The motor has very different "resistance" depending on the load case. In this case, 166 Ohm equivalent running free vs. 10 Ohm equivalent when stalled, calculated from current values in the datasheet. You have to decide for a use case. \$\endgroup\$
    – posipiet
    Commented Feb 21, 2012 at 17:39
  • \$\begingroup\$ I think I've found an alternative solution. I'll simply bend the pin so it doesn't make contact with the VIN on the arduino. \$\endgroup\$
    – Hilydrow
    Commented Feb 21, 2012 at 18:17

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