Page 103 - Robot Builders Source Book - Gordon McComb

communications-infrared
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Help—My Remote Control Won’t Work!
A number of robot toys and kits come with an infrared hand-held remote control, the
same kind of thing you use to channel surf on your TV. Their operation is simple: Press a
button and infrared light flashes from an emitter on the front. A sensor on the robot
receives the flashes, decodes them, and responds to the command you have given.
Alas, for something so simple, remote controls don't always work as expected. And it's
not always because the batteries are dead—though that's a leading cause. So, if the
remote control for your robot has stopped functioning, review these points to get it back
on track.
• Dead or corroded batteries. This has to be mentioned, simply because it's so obvious.
Open the battery compartment and look for corroded battery contacts. If a battery has
leaked, clean the battery contacts with a pencil eraser or battery contact cleaner. Wash
your hands thoroughly to remove residue battery electrolyte. Replace with known, fresh
batteries.
• Batteries inserted incorrectly. Be sure the batteries are not reversed when you insert
them in the remote. Otherwise the remote will not work, or it will work erratically.
• Bent battery contacts. Replacing batteries all the time in the remote can bend the bat-
tery contacts inside. Be sure they make a good physical connection to the terminals on
the battery.
• Dirty or gummed up contacts. Spilling a drink into the remote control is a sure-fire way
of ruining it. Water and diet sodas will usually dry, and the remote will come back to life.
Sugared sodas, coffee, and milk will leave a residue, requiring the remote be disassem-
bled and cleaned or thrown away.
• Obstruction or dirty LED.* Same for the infrared receiver. Look for tape, a broken piece
of plastic, dirt, or crud covering the LED on the remote control. Do the same for the
infrared receiving module on the robot.
• Bad infrared LED. This is less common, but it can happen if the remote is used a lot.
You can try replacing the LED. Most any high-intensity LED will work, but be sure to
observe correct polarity.
• Bad IR sensor. This can happen too, though it is unlikely. The sensor can be replaced
with a new one. This is much easier if the robot was built from a kit, where you can pur-
chase a direct replacement from the kit maker.
(*Some of you may object to using the term LED—light emitting diode—for an infrared
emitter. While they technically do not emit light visible to the human eye, it is indeed visible
light to other animals, such as cats, as it is in the near-infrared region of the electromag-
netic spectrum. Therefore, LED is the correct term.)
Testing the Remote Control
There are several simple ways to test if a remote control is working. One easy approach
is to place the remote near an AM radio. Dial to a position where there is no station (a
distant station is okay). Press buttons on the remote. You'll be able to hear a high-pitched
“trill” sound as you press the buttons. If you do not hear the sound, the remote is not
working at all.
In instances where the basic electronics of the remote are working, but its infrared LED
is not, you can test this with an LED sensor, available at RadioShack and many other elec-
tronics stores. The sensor is a passive device: It glows after exposure to a bright infrared
light source.