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Many of the microcontroller projects here on MAKE control small things like LEDs, but what about large motors? Roger writes –

This tutorial offers suggestions about controlling large loads with a microprocessor. This is often an issue with those building robots who need to control devices such as lights, motors, vacuums, and other accessories found on robots. We will only deal here with devices that need to be switched ON and OFF – not devices that need the power reversed. Obviously drive motors and other devices need to be switched ON/OFF and also have the power reversed in order to reverse the direction of the motors. That normally requires an H-bridge which is a much more complicated circuit.

Driving high-power loads with a microprocessor – Link.