Build Your Own Combat Robot

292 Build Your Own Combat Robot
Once the circuit is built, put a small tube around the LEDs to help focus and
collimate the infrared light. Although most of the light is projected in front of the
LEDs, a small fraction of the light goes sideways and to the rear of the LED. This
could interfere with the infrared receiver module, causing false readings. The
tubes also help reduce this interference. The IR receiver modules that are not enclosed
inside a metal case, such as the Panasonic PNA4602M, are very susceptible
to this setback. To solve this problem, place a small piece of aluminum foil duct
tape on the back and sides of the receiver module. Do not let the tape touch the
wire leads. This will help prevent false readings from sideways and backward
emitted IR light.
The basic operation of this circuit is to flash the left IR LED, then take a reading
from the IR receiver, then flash the right IR LED, and then take another reading
from the IR receiver. If the receiver detects something from the left IR LED, then
there is something that is either to the left front or in front of the detector. If the receiver
detects something from the right IR LED, then there is something either to
right front or in front of the detector. If both left and right IR LEDs returned a signal,
then there is something directly in front of the detector. Using this approach, a relative
direction of the object can be detected. The left and right angular range detection
can be adjusted by angling the IR LEDs toward or away from the IR
receiver module.
Depending on which infrared receiver module you choose, the modulated infrared
light must be on between 400–600µs to allow for the receiver module to
stabilize. Otherwise, a false signal is more likely to occur. In the real world, there’s
a lot of “noise” in all signals, so it’s better to take a sample of readings instead of
relying on a single measurement. One method of sampling is to take five consecutive
readings. If you get more than three hits, there is a greater probability that
there is an object in front of the sensor.
A 40-kHz infrared receiver module has its peak sensitivity at 40 kHz. They are
still functional when receiving light at +/- 5 kHz of the center frequency. The further
away the actual modulated frequency is from the center frequency, the less sensitive
the sensor becomes. With this knowledge, the sensitivity of this circuit can be adjusted
by shifting the modulated infrared LED frequency away from the center frequency.
The reason this may be important is that the detector circuit will detect
white objects that are much farther away than black objects. Also, the ambient
lighting at an actual competition is usually different that the ambient lighting at
home or wherever you’re building and testing your bot. Sensors usually respond differently
in the different ambient lighting conditions. Having the ability to adjust the
sensitivity of the detectors will improve your bot’soverall performance.