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RR1 • 5
RR1 THEORY OF OPERATION
The RR1 may look simple but there is actually quite a lot being done inside
each one of the parts. Many individual components are packed inside of the
IR receiver part (U2) itself; so many in fact that if it was built up with discrete
components, it would never fit in this little kit case. Inside of the part there is
an IR detector diode, amplifier, AGC circuit, bandpass filter, a peak-hold cir-
cuit, an integrator, comparators, and an output amplifier. Heck, the part is a kit
in itself! Just be glad it’s all in one nice module and ready to go.
IR remote controls send out their data on a 38 kHz carrier much like the way
your FM radio does. By modulating the carrier signal with the data you want to
send, it is possible to increase the range of the transmission and decrease in-
terference from other IR sources like ambient light (the sun pumps out lots of
IR!!!). The modulation style used with remotes is called OOK (on off keying).
In a nut shell, OOK modulation means the IR LED is switched on and off at a
rate of 38 kHz in order to send the needed data. The digital data being sent
(ones and zeros) is composed of a certain duration pulse for a one and a dif-
ferent duration pulse for a zero. There are pauses with no carrier in-between
each one and zero data bit being sent for easy determination of the bit
boundaries. A common format for this type of data transmission is called
60/30 PWM. While this may sound complex, it really is not. Let’s take a closer
look.
PWM stands for Pulse-
Width-Modulation (not
Pretty-Wild-Muscles). In
our case this means that
we change the amount of
time the IR LED is turned
on versus off in accor-
dance with the data we
want to send. For exam-
ple, let’s say we’re send-
ing data at a rate of 1 bit
per second (bps). Each bit would take one second to send. To represent a
logical one, the LED must be switched on and off at a rate of 38 kHz for 60%
0
1
0Sec 1Sec
0
1
0Sec 1Sec
IR Remote
Output
IR Detector
Output