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Amphibionics 05 3/24/03 8:44 AM Page 154
Amphibionics
Calibration
To calibrate the infrared sensor board, a multimeter with frequen-
cy measuring capabilities like the one shown in Figure 5.46 will
be used. Connect a 5-volt DC source to the circuit, as shown in
Figure 5.47. Connect the positive lead of the multimeter to the
point shown in Figure 5.47, and connect the common lead to the
circuit ground. Set the multimeter to read frequency. Use a small
screwdriver to adjust potentiometer R3, until a frequency of
approximately 43 kHz is displayed. This will adjust the circuit so
that the 555 timer is producing a 5-volt square wave that will
modulate the infrared LEDs at a frequency that is close to where
the PNA4602 sensor module will respond. The circuit frequency
will be fine-tuned with a software routine later in the chapter.

FIGURE 5.46
Fluke 87 digital
multimeter with
frequency measuring
capabilities.

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