9 years ago.

For a low power motor the most simple method is to use a transistor to switch the power to the motor on and off. This would require that the motor and the mbed have a common ground connection.

For higher powers or if you want to completely isolate the motor power supply from the mbed then you should use a relay.

Google will give you lots of example circuits for how to do this.

9 years ago.

Are you attempting to control a 2-wire, 3-wire, or 4-wire fan? The answer from Andy A is the right way for a 2-wire interface. If you have a 3 or 4 wire interface then it would be different.