Build Your Own Combat Robot

Chapter 11: Autonomous Robots 255
trols the 40-kHz modulation frequency. Using a 10-turn potentiometer will give you
the best sensitivity control. To adjust this circuit, you first adjust R2 to 550 Hz,
700 Hz, 850 Hz, or 1000 Hz. You will need an oscilloscope or a multimeter that can
measure frequencies. You will measure the carrier frequency from pin number 5.
After the carrier frequency is set, then temporarily ground pin number 6 and adjust
R6 until you get 40 kHz. You will monitor the 40-kHz frequency from pin 9. When
you are done, remove the temporary ground from pin number 6.
For those of you who are mathematically inclined, the frequency carrier frequency
is shown in equation 5, and the modulation frequency (the 40-kHz frequency) is
shown in equation 6.
To set up an autonomous system on your robot, you will have to build a circuit
to decode the infrared signals your receiver unit detects from the beacons. You can
use either hardware or software to decode the signals. With either method, you
will need a microcontroller to interpret the results and plan the attack. A software
method would measure the pulse length out of the receiver unit. Total pulse length
is calculated from the modulation frequency, as shown in equation 7. The
microcontroller will look for one-half the total pulse length, either the positive or
negative portion.
A simple logic statement for detecting a 700-Hz signal might look like this:
IF [(Pulse_Width is greater than 650 microseconds)
and (Pulse_Width is less than 750 microseconds)]
THEN Beacon_Frequency is 700 Hz
With a Basic Stamp, to measure the pulse width can easily be accomplished using
the Pulsin command. Using software to analyze the infrared frequencies can
simplify the number of components that go into the robot controller and can give
you more options in configuring your robot to attack. Programs can be changed
between matches to account for conditions not originally accounted for. But software
solutions are sometimes complicated to implement, depending on your programming
skills.
A hardware solution can be simple. Figure 11-9 shows a schematic drawing of a
circuit that uses the 567-tone decoder to interpret the carrier frequency from the
infrared beacon. Potentiometer R1 is used to adjust the frequency this circuit will
detect. A 10-turn potentiometer will give you the greatest sensitivity control in adjusting
the desired frequency. To adjust this circuit, place the test infrared beacon
in front of the receiver module and measure the voltage from pin number 8. Adjust
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11.6
11.7