Unused button pads
9V battery connector
Slide-off battery cover
Connection to radio board below
Wire link on
underside of board
Signal from Bit Whacker
Data signal from MCU to radio transmitter
D Original signal from MCU
sets would work without interference, but I noticed
that if you left the remote’s battery disconnected for
a while, you had to retrain all the outlet units.
The only explanation I could think of for this was
that the remote generates a new unique identifier
when it powers up, which the outlet units store during the learning process. If so, this was a good sign,
as it suggested that you could co-locate 2 or more
sets (and other similar devices), provided that their
remotes used different identifiers.
So far so good, except that you’d still need a
separate remote for every 3 units, which would get
out of hand if you wanted to control a lot of devices.
To find better alternatives, I opened up the remote
control unit. The main circuit board housed button
pads, an Elan EM78P153SNJ microcontroller (MCU),
a 5V regulator, and an LED (Figures B and C); underneath it sat another board with the radio transmitter
circuit and antenna.
There was enough room inside the remote to hold
a small microcontroller board. A microcontroller
wired to the button contacts could then simulate
button presses on the remote, and you could plug
its USB interface into a computer to pass switching
control over to the computer.
Also, the main board had unused pads for an extra
pair of buttons, so it looked like you could easily wire
the remote to control 4 devices instead of 3. By wiring
into the remote like this, you don’t need to modify
the power outlet units at all; they remain safely intact
with all their approvals (FCC, CE, UL, etc.).
But 4 devices per remote still isn’t much, so
I decided instead to try and intercept the data
signals being sent from the remote’s microcontroller to the radio transmitter circuit on the board
underneath. If I could decode these signals, then
I could also generate my own signals and control
lots more devices, if the protocol allowed it.
R/C power outlet system I used a Maplin N19GN,
which works for mains in the United Kingdom,
and my code is tailored to its wireless protocol.
You’ll want to use a system with the appropriate
power connectors and ratings for your country.
USB Bit Whacker microcontroller board
part #DEV-00762 from SparkFun Electronics
Insulated hookup wire
Soldering supplies, and a screwdriver
PC computer with USB cable