Low cost RC power sockets (radio outlets) + Arduino

[Deutsche Version]

For cheap home automation purposes I’d like to present you my new Arduino libary for operating up to 16 low cost 433MHz RC power sockets. I’ve bought this RC switch set for about 10 EUR.

There is a SC5262 chip (datasheet) built in the hand set which – depending on which key is pressed – generates a data telegram and relays it to the actual RC sender. After studying the datasheet and some other resources (1, 2, 3 – sorry, all in german) on similar projects I was able to control the switches using only one I/O pin at the Arduino.

Theory
If you know how the data telegrams look like, you can generate them with the microcontroller and therefore resign the encoder chip from the hand set.

A code bit consists of two on/off states. The important thing are the cronological lengths of these states. You can think of it like morse. There are thre possible code bits at all, that is „0“, „1“ and „F“. Furthermore there is another sync. bit (I’ll call it „S“).

"0" Bit => 1/8 cycles on, 3/8 cycles off, 1/8 cycles An, 3/8 cycles off   -...-...
"1" Bit => 3/8 cycles on, 1/8 cycles off, 3/8 cycles An, 1/8 cycles off   ---.---.
"F" Bit => 1/8 cycles on, 3/8 cycles off, 3/8 cycles An, 1/8 cycles off   -...---.
"S" Bit => 1/8 cycles on, 31/8 cycles off -...............................

A code word consists of 9 address bits, 3 data code bits and one sync. bit. It represents the command (data bits) to a specific switch (address bits).

A code frame consists of 4 code words. Basically every command is repeated 4 times.

The conrad power switches are coded as follows:
4 bits group address + 4 bits switch address + 1 unused adress bit + 1 unused data bit + 2 data/command bits + 1 sync. bit


group address I = "0FFF"
group address II = "F0FF"
group address III = "FF0F"
group address IV = "FFF0"

switch 1 = "0FFF"
switch 2 = "F0FF"
switch 3 = "FF0F"
switch 4 = "FFF0"

unused databits = never mind, could be either "F" or "0"

command on = "FF"
command off = "F0"


So if you want to switch the 3rd switch from the 4th group off, you’ll have to send „FF0FFFF0FFF0S“.

Hardware / Hacking the hand set

Open your hand-held transmitter and solder a wire to the positive pole (+), one to the negative pole (-) of the battery holder and another one to the DOUT Pin of the SC5262S chip.
Altough my transmitter was operated with a 12V battery it also worked with 5V, so I think it’s fine to power it directly from the Arduino (5V and GND). Connect DOUT to any available I/O pin from the Arduino.

Software
Download RCSwitch.zip and extract it to your /Arduino/Libaries directory. The following sketch should be self explaining 🙂

#include <RCSwitch.h>

RCSwitch mySwitch = RCSwitch(11);  // Sender is connected to Pin #11

void setup() {
}

void loop() {
    mySwitch.switchOn(1, 1);         // Switch 1st socket from 1st group on
    delay(1000);
    mySwitch.switchOff(1, 1);        // Switch 1st socket from 1st group off
    delay(1000);
}

Updates

• The libary is hosted at google code now (here).
• New sending methods (other outlet types than described here or raw codes)
• New functionality to receive and decode signals from your remote hand set