Specifications

27
4.4 H-Bridge Motor Control
After having the mechanical unit constructed, encompassing the microcontroller and
odometry sensors, it was necessary to decide on a method to control the motors. Two H
bridges were sourced from the technician’s lab at USQ to allow the microcontroller to
handle the large current flows. An H bridge works by a series of four switches which
can control the current flow through the motor. The schematic below shows the basic
operation of the common H Bridge. The grey arrows represent the current flow through
the motor.
Figure 4.9: Basic H Bridge Operation
By applying a small voltage such as logic high from the Motorola HC12, the switches
can be turned on to allow current flow and hence motor operation. Only diagonally
opposed switches should be turned on at the one time. If both switches on one side are
turned on at the same time a short circuit is made from the positive to negative voltage
supply. This is often referred to as shoot through.