Theory Of Operation - Ramsey Electronics ICI2 Instruction Manual

ICI2 THEORY OF OPERATION
The ICI2 may look quite simple, but there is actually quite a lot to it inside the
parts. Many items are inside the IR receiver part (U4) that if built up with dis-
crete components would never fit in this little kit case! Inside this part there is
an IR detector diode, amplifier, AGC circuit, bandpass filter, a peak-hold cir-
cuit, an integrator, comparators, and an output amp. Heck, the part is a kit in
itself! Just be glad it is in one nice module all ready to go.
Your IR remote control sends data on a 38kHz carrier, much like an FM or
AM radio does. It does this to increase range, and decrease interference from
other IR sources such as ambient light. It is done in an OOK (on off keying)
fashion, meaning that the IR LED is switched on and off at a rate of 32kHz for
a certain duration for a one, and another certain duration for a zero, with
pauses of no carrier in-between each one and zero. A common remote control
format does some special things to differentiate a one from a zero for digital
sending and receiving of data.
When the IR detector "sees" a 38kHz IR signal, the output of the detector
goes low (it is inverted), when there is no 38kHz signal, the output idles high.
On the output of the IR detector you won't see the 38kHz, just the data that
the 38kHz represents from your IR remote control. This allows the remote
control to save power since the IR LED is on a minimal amount of time.
Typically a remote control will send data in a format consisting of time slices.
0 Bit
1 Bit
To send a zero, the IR LED will be off
for one time slice, and then toggled at
a rate of 38kHz for the second time
slice. To send a one, the IR remote will
use three time slices. Off for two time
slices, and on for one. This makes
things easy on the receiver side, be-
cause we just have to look from the
edge of the first on-to-off transition to
the middle of the second time slice (1
1/2 time slices from the start) to deter-
mine the bit that was sent.
ICI2 Page 5