>I was in a car repair workshop yesterday & I saw a poster advertising
>cloning of your remote control for your car door opener & car burgler
>alarm. The poster had a photo of their clone & it had a PIC 1654 in it.
>There didn't appear to be much more to it at all - one transistor, 1
>capacitor, an LED & maybe a coil. It had 4 buttons & apparently each button
>is dual purpose (whatever that means).
>
>Anyway, this has me really interested - I would love to be able to get hold
>of something like this - the units are being sold for US$35 each, but the
>main problem is that they do not sell any type of receiver - they only
>clone existing transmitters.
>
>Does anyone know of a circuit diagram for the transmitter & receiver for
>this toy? I actually want to transmit data back from a robot to my PC, so
>this small multi-channel transmitter would be perfect as these remote
>controllers normally have a good range & don't need line-of-sight. Failing
>that, are they available commercially - tx & rx at a reasonable price? I
>definitely prefer PIC based units, as I already have the development
>software & hardware & a little bit of experience with them.
>

The canned modules available from Digi-Key are probably a good way to get
familiar with the technology and do the robot project.  For someone more
interested in how the transmitters and receivers work, and eventually hoping
to spend less than $11.00 each for them, here is what I know about them:

The frequency in the US is usually 310-315 MHz.  On/off keying is used with
digital modulation of about 1 Kbaud.  Usually pulse-duration,
pulse-position, etc. coding is applied.  The transmitter RF hardware is thus
a simple L-C oscillator with provision for switching it on and off by
digital control.

The receiver is almost always a super-regenerative type.  Overall, it's an
RF amplifer with intentional feedback so it wants to oscillate.  The signal
from the antenna is coupled into it.  While a signal is present, this will
cause the oscillation to become stronger.  Using positive feedback
theoretically increases the gain of a single amplifier stage to infinity,
though at the price of stability.  Sometimes, though not usually, a
conventional RF amplifier stage is added before the regenerative one.  This
helps keep the oscillations from back-coupling out on the antenna as well as
improves sensitivity.

In order to keep the receiver from simply locking in an unstable mode (i.e.
becoming a transmitter, one reason the regenerative is not used for general
radio devices any more), a second R-C feedback path is present that makes
the overall bias oscillate between the unstable and stable regions at about
500 KHz.  The average time spent in the stable region is longer if no signal
is received at the antenna.  The operating voltage or current changes
depending on whether it is oscillating or not.  This voltage or current,
filtered of the 500 KHz self-oscillation but still containg the 1 Kbaud
modulation, is then amplified with an op-amp or similar device up to digital
levels and then decoded.  This kind of receiver doesn't work particularly
well, but for short range and low selectivity that is required of alarm
remotes and garage door openers, it does fine.

For a 'cloning' device, assuming the transmitter can be held very close
during the copying process, a simple diode-detector receiver would probably
work.  This function could probably be shared with the transmitter by using
the transmitter at low or no bias and rectifying the signal picked up by the
antenna.

-Mike