Page 91 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

Tuning the transmitter Set up the infrared diode and receiver module
next to one another facing in the same direction. The LED must be
completely encased in a tube of some sort that only permits the in-
frared light to leave from the front of the LED. Failure to do this will
make using this setup impossible. Note that some plastic materials
while opaque to visible light are completely transparent to infrared
light.
Place a white card about 3″ in front of the transmitter and receiver.
Turn on the circuit. Adjust R1 until the receiver’s LED turns on.
Then remove the white card. The receiver’s LED should go off. If it
doesn’t, the infrared LED on the transmitter may be leaking light
from the side and activating the receiver.
Once the unit is working properly, the circuit can be fine-tuned to
detect objects at a greater distance. Move the white card back in
front of the transmitter and receiver until it just triggers the LED
to turn on. Adjust the potentiometer (slightly) on the transmitter
so that the LED turns on completely. Keep in mind that it may not
be advantageous for the robot to detect objects and/or collisions
that are too far away.
DTMF IR communication/remote control system
70
Other authors have detailed the use of IR transmitters for communi-
cation and remote control. Typically the IR transmitter is modulated
at a particular frequency and the receiver unit utilizes a 567 phase-
locked loop (PLL) integrated circuit (IC). While this works, one
must match and tune each transmitter-receiver pair. There is an
acceptable way to work around this.
Integrated circuit chips designed and manufactured for the telecom-
munications industry are readily available. These inexpensive chips
are capable of transmitting and receiving 16 distinct signals, no
tuning required. By coupling these chips to standard IR components,
an IR remote communication/control system can be implemented.

DTMF
The dual-tone multifrequency (DTMF) signal was originally devel-
oped just over 25 years ago. This was before the U.S. government
forced Bell Telephone to break up, allowing the company to expand
into other markets. DTMF is commonly known as touch-tone dialing.

The standard DTMF signal is composed of two audio tones gener-
ated from a group of eight possible tone frequencies. The eight
frequencies are divided into two equal groups, a low-frequency

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Chapter five