Build Your Own Combat Robot

FIGURE 11-3
Sharp PG2D02
Infrared range
sensor. (courtesy
of Acroname, Inc.)
Sharp GP2D02 and GP2D12 Infrared Range Sensors
Chapter 11: Autonomous Robots 245
The GP2D02 and GP2D12 are infrared range finders. Shown in Figure 11-3, these
sensors work by transmitting an infrared light and measuring the location of the
reflected light on a position sensitive detector (PSD).
Next, you can see how this sensor works. By using a triangulation method, the
range of an object can be determined by the location at which the reflected light hits
the PSD. The detection range for these sensors is from 4 inches to 31 inches (10 cm
to 80 cm). The GP2D02 outputs an 8-bit serial data set. As the object gets closer to
the sensor, the output number gets larger. The maximum number occurs with a distance
of about 4 inches, and the smallest number occurs out past 31 inches.
The GP2D12 works similar to the GP2D02, except the output value is an analog
signal—in other words, it is a variable voltage that will range from 0 to 3 volts. The
maximum voltage will occur at 4 inches, and the minimum voltage will occur out
past 31 inches.
Sharp GP2D05 and GP2D15 Infrared Proximity Sensors
The GP2D05 and the GP2D15 are infrared proximity sensors that look physically
identical to the GP2D02 and the GP2D12 sensors. The difference between these
sensors is that the output signal changes when the object moves past a preset distance
of 9.5 inches (or 24 cm). For any object that is between 4 inches and 9.5 inches (10 to
24 cm), the output signal is 0 volts, and any object that is past the 9.5-inch threshold
will have a positive 5-volt output signal. The difference between the GP2D05
and the GP2D15 sensors is that the GP2D05 sensor requires an input trigger pulse
to tell the sensor to make a measurement. The GP2D15 sensor continuously takes
measurements.
note The case of all four of the GP2Dxx sensors looks like normal black plastic, but it is
actually a good electric shield when grounded. It is very important that you connect this shield
to ground. This is mandatory for these sensors to work reliably!
Thermal Sensors
One of the more popular types of sensors to measure temperature is the thermistor,
a sensor whose internal resistance changes with temperature. By measuring