Hardware Reference
In-Depth Information
of them are listed on the Arduino playground at
http://
arduino.cc/playground/Main/InterfacingWithHardware
.
You'll see one in action in the next project.
LED, and a receiver that listens for the carrier wave and
demodulates the data signal. It's possible to build your
own IR modulator using a 555 timer IC, but there are a
number of inexpensive modules you can buy to modulate
or demodulate an IR signal as well.
X
If you're building both the transmitter and receiver, your
job is fairly straightforward. You just need an oscillator
through which you can pass your serial data to an infrared
Sniffing Infrared Signals
An oscilloscope is also useful when you're trying to
decipher an IR signal (see Figure 6-4). You may not know
the protocol for your receiver, but you can work it out by
looking at the signal it sent. Connect an infrared photo-
transistor, a resistor, and a regular LED in series, as shown
in Figure 6-5, and you should see the LED light up when
you point your remote at the phototransistor.
To see the remote's signal on an oscilloscope, connect
the scope probes to ground and to the phototransistor's
emitter, and fire the remote at the phototransistor. Once
you see activity, adjust the voltage and time divisions on
Figure 6-4
. An oscilloscope can help you see the pattern of
an IR signal.
MATERIALS
» 1 solderless breadboard
» 1 220-ohm resistor
» 1 phototransistor
Digi-Key part no. 365-1068-ND.
» 1 LED
» 1 battery or power source
5V or less.
» 1 oscilloscope
DSO nano shown here.
1
5
10
15
20
A
B
C
D
E
F
G
H
I
J
1
5
10
15
20
the scope until you see readable activity. Most scopes will
tell you the frequency of the signal automatically. Putting
your scope in single-shot trigger mode will help you capture
the actual signal. Once you can see the timing of each
signal's pulse, you can work out how to duplicate it by gen-
erating your own pulses on an IR LED. For more on this, see
many of the excellent blog posts on IR remote control using
an Arduino. For example, read Ken Shirriff's very good expla-
nation on his blog, at
www.arcfn.com
.
Figure 6-5
. An IR phototransistor and LED in series work
well to test IR reception.
