The robot consists of modules controlled by a main controller. The main microcontroller
is an 18-pin, 8-bit, PIC16F84 Flash microcontroller operating at 4MHz.
The microcontroller is programmed in assembly language. The controller is
connected via I/O pins to the communication module, drive module, scoreboard
and the stepper motor driver circuit. The controller is responsible for processing
the input received from the receiver module and executing the necessary responses.
The transmitter is controlled by an 8-pin, 8-bit PIC12C509A microcontroller
programmed in assembly language. The main controller outputs control signals
to the transmitter via two output pins. One pin controls the laser and the other
enables the infrared transmitters. The output from the laser is a stream of bits
decoded by the opposing robot as a hit. The output to the infrared
transmitters allows the transmitter to be turned on and off by the controller.
The receiver is a PNA4613M photo IC. The controller receives input signals from the
receiver module via an input pin. The data sent by the receiver module is a stream of bits
corresponding to the infrared signal received. The controller processes the signal and
responds to valid data received.
The scoreboard is controlled by an 8-pin, 8-bit PIC12C509A microcontroller.
The microcontroller is programmed in assembly language. The scoreboard connects
to the main controller via an input pin. The input pin is polled continuously. The main
controller toggles the input to the scoreboard high to increment the hit count on the
The L293D is a dual h-bridge driver IC. The IC is also referred to as a push-pull
four channel driver. An h-bridge is ideal for driving motors. The L293D provides
two h-bridges for driving both motors on the robot base. The motor direction is
controlled by logic signals from the microcontroller. Two signals per motor are
required to control the direction
The Low Battery Indicator circuit was designed with the availability of parts, and low
cost in mind. The circuit is based to the LM741 operational amplifier. The op amp
is configured as a comparator. A zener diode provides a voltage reference to the
non-inverting input of the comparator. A voltage divider between the battery voltage
and ground is connected to the inverting input. When the voltage of the divider drops
below the reference voltage then the output of the comparator goes low and lights a
red LED (tied high).
Charging of sealed lead acid (SLA) batteries has a significant effect on the performance
and service life of the battery. The charger developed for the robots’ SLA batteries
was designed to meet the specifications of the battery as given above. The charger
design is based on Unitrode’s UC3906 battery charge controller IC. The charger is
a dual-level float charger. An important feature of the UC3906 is that it is temperature
compensated to track the battery temperature coefficient.