Build Your Own Combat Robot

254 Build Your Own Combat Robot
FIGURE 11-8
Infrared test beacon
circuit. (courtesyof
Bob Gross)
quency, so different beacons could be distinguished between each other. The four
different modulation frequencies were 550 Hz, 700 Hz, 850 Hz, and 1000 Hz.
The reason for using the 40-kHz carrier frequency was so that standard infrared
remote control receiver modules could be used to detect the infrared light from
the beacons. A set of these sensors could be placed around a robot to look for the
beacon, and once it detected the beacon, the robot homed in on the beacon to initiate
the attack. The infrared receiver modules were the same type of receiver module
found inside television sets and video cassette recorders. Most electronic
component stores sell them. Some models that work well with the 40-kHz signal
are the Sharp GP1U58X, the Sharp GP1U59Y, or the Liton LTM97AS-40. These
sensors specifically look for a 40-kHz signal, and they will ignore signals outside
+/– 5-kHz tolerance band.
With this type of system, a beacon was placed on top of each robot in the match
and the robots tried to find each other. The robot builder was responsible for de
veloping the electronics and software for detecting and decoding the infrared signal
from the beacons. Each robot was not allowed to use its own beacon design in
combat, since the event coordinators provided them, or they were not allowed to
transmit false infrared signals to confuse the opponent.
Figure 11-8 is a schematic drawing showing how to build a simple test beacon circuit.
This circuit will generate the 40-kHz modulation signal and the 550- to 1000-Hz
carrier frequencies. Resister R2 controls the carrier frequency, and resistor R6 con-