Specifications

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control the frequency. By setting a number between $01 and $FF in the PWPER (0-3)
registers, the pulse frequency can be set to a proportion of this clock rate. The duty
cycle of this frequency can then simply be controlled by storing values between $00 and
$FF into the PWDTY (0-3) registers. This value represents the proportion of high over
low time; hence $FF/2 would be 50% duty cycle and the motor would be running at half
speed, or $00 would stop the motor.
It is important to not switch the H Bridge switches too fast in this application.
Transistors require a small amount of time to switch on or off. It is because of this time
that causes a current flow and hence a power loss. Over switching at high frequencies
will increase the power consumption and therefore create heat from the MOSFET’s.
Heat sinks are installed on all of the robots MOSFET’s to compensate for the switching
power loss.
To conclude on motor control, the Mobile Manoeuvring Robot is controlled by two
identical H Bridges which are powered from a 10 – 12 volt source. The motor speed is
determined by four separate Pulse Width Modulation Channels with a relatively low but
fixed frequency and variable duty cycle.
4.5 Infrared Distance Sensors
4.5.1 Requirements and Availability
The current market offers many types of sensors for use in various applications. A few
of the major types of sensors include:
• Optical sensors
• Photo diode sensors
• Fibre optics sensors
• Proximity sensors
• Ultrasonic sensors.