Build Your Own Combat Robot

FIGURE 13-10
Infrared object
detector schematic
drawing.
Chapter 13: Robot Sumo 291
A simple infrared object detector consists of two infrared LEDs, a 40-kHz frequency
generator, and a 40-kHz infrared receiver module. For robotic object detection
applications, a modulated LED is mounted on both sides of the receiver
module pointing slightly away from the receiver module. By alternating which
side of the LED is active, you can determine which side the object is on.
The schematic shown in Figure 13-10 is for a simple infrared object detector using
a few common components. This circuit uses a single 74HC04 CMOS hex inverter
to generate the 40-kHz modulated signal, and act as switches to turn on/off
the modulated infrared LEDs. The potentiometer R1 is used to adjust the modulated
frequency. When selecting the infrared LEDs and the infrared receiver module,
make sure that they are both sensitive to the same wavelength.
The two most common wavelengths are 880nm and 940nm. For the Sharp detectors
that come inside a metal can, the metal case must be grounded to the rest of the
circuit. Resistors R4 and R5 can be decreased in value to increase the range of the detector.
To turn on the infrared LED, apply 5 volts to the particular LED signal line.
To turn it off, ground the signal line. The output of the infrared receiver module is
normally high at 5 volts. When it detects the proper modulated infrared light, the
output voltage will drop to zero.
The Sharp G1U52X and GP1U581Y series infrared receiver modules are the
most common, and the Panasonic PNA4602M series infrared receiver modules
are becoming more popular since they are less sensitive to visible light than the
Sharp detectors, and they are less than half the size of the Sharp detectors.