My daughters model boat required a speed controller with forward and reverse control. Over a couple of evenings this simple speed controller for brushed motors was developed.It uses a 6 transistor H-bridge drive. Two PNP power transistors are used for the source side of the H-bridge and two NPN power transistors of complimentary characteristics are used for the sink side of the H-bridge. The bases of each sink-source pair are connected by a small NPN transistor. This allows just two lines to control the H-bridge drive. This allows forward, reverse and off control of the motor. Braking cannot be acheived with this type of H-bridge. Bipolar transistors are used because the efficiency required for this controller is low.
The H-bridge is controlled by a small micro-controller, PIC12F675. It utilises its external interupt pin to monitor a standard PWM RC servo control signal to control the duty cycle and direction of the H-bridge. The motor is driven by forcing one one of its inputs high, the input is also PWM with 206 levels of duty cycle. Thus direction and speed of motor is controlled.
Circuit schematic, PCB layout and PIC code are available free at www.infracortex.com. Also it is intended that this controller with be developed into a speed controller with current and rpm feedback so keep upto date with events here.
