Page 173 - Amphibionics : Build Your Own Biologically Inspired Robot

Amphibionics 05 3/24/03 8:44 AM Page 152
Amphibionics
The sensor board works by producing modulated infrared radia-
tion with an infrared LED and using the PNA4602 module to detect
any radiation reflected from the surface of solid objects. The
PNA4602 sensor is designed to respond only to infrared that is
modulated at a frequency somewhere between 38–42 kHz. The
circuit is tuned to modulate the infrared LED at this frequency.
Depending on the proximity of the sensor to the object, a greater
or lesser number of infrared pulses will be reflected back. The
number of reflected “hits” that the sensor receives in a given time
frame allows the robot to determine how close it is to objects. The
higher the number of reflected pulses, the closer the sensor is to
the object. The output pin from the PNA4602 is connected to a
microcontroller input pin, and a software routine is used to mon-
itor the sensor.

Constructing the Infrared Sensor Circuit Board
To fabricate the PCB, photocopy the artwork in Figure 5.43 onto a
transparency. Make sure that the photocopy is the exact size of the
original. After the artwork has been successfully transferred to a
transparency, use the techniques outlined in Chapter 2 to create a
board. A 4-inch 6-inch presensitized positive copper board is
ideal. When you place the transparency on the copper board, it
should be oriented so that it is exactly the same as in Figure 5.43.

FIGURE 5.43
Infrared sensor board
PCB foil pattern
artwork.

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