Some experiments on Radio Remote Controls

Arduino and Radio Controller Sockets

I have bought a kit by avidsen including a socket and a remote.

My goal was twice. I wanted to control avidsen sockets using an arduino and to get commands from a avidsen remote.

For that I have taken a set of RX and TX 433.92Mhz modules. This kind of modules are very common on e-bay.

They are usually provided without an antenna: they need a 17.3 cm wire soldered to the ANT labelled terminal.

There is already a library named RC-Switch. It can be downloaded from github. This is its latest release: https://github.com/sui77/rc-switch/releases/tag/v2.52.

The library includes a set a of examples. I have created a specific sketch for my avidsen set.

The wiring between the Arduino and TX/RX modules is:

TX has three pins 
(left to right watching the component side of the PCB, there are clear labels):
   DATA <-> Arduino GPIO 2
   Vcc  <-> Arduino 5v
   GND  <-> Arduino GND

RX has four pins 
(left to right watching the component side of the PCB, the labels are printed on the reverse side of the PCB)
   Vcc  <-> Arduino 5v
   DATA <-> Arduino GPIO 10
   DATA <-> (the two DATA pins are connected together, so either can be used).
   GND  <-> Arduino GND

#include <RCSwitch.h>

RCSwitch mySwitch = RCSwitch();

#define BINARY 0
#define SWITCH 1
int mode=SWITCH;

void setup() {
  Serial.begin(115200);
  mySwitch.enableReceive(0);  // Receiver on inerrupt 0 => that is pin #2
  mySwitch.enableTransmit(10);
}
 
void incodeProcess(unsigned long code) {
	static char outbuf[25];
	int i;
	switch (mode) {
		case BINARY:
			for (i=0; i<24; i++, code>>=1) 
				outbuf[23-i] = (code & 1) ? '1' : '0';
			break;
		case SWITCH:
			outbuf[5]=outbuf[11]=' ';
			outbuf[13]=0;
			switch (code & 0xF) {
				case 0x1: outbuf[12]='1';break;
				case 0x4: outbuf[12]='0';break;
				default: return;
			}
			code>>=4;
			for (i=0; i<5; i++, code>>=2)
				outbuf[10-i] = (code & 1) ? '0' : '1';
			for (i=0; i<5; i++, code>>=2)
				outbuf[4-i] = (code & 1) ? '0' : '1';
			break;
	}
	Serial.print(outbuf);
	Serial.println();
}

void inlineProcess(char *line) {
	if (line[5] == ' ' && line[11] == ' ' && line[13] == 0) {
		line[5] = line[11] = 0;
		switch (line[12]) {
			case '1':
				mySwitch.switchOn(line,line+6);
				break;
			case '0':
				mySwitch.switchOff(line,line+6);
				break;
			default:
				return;
		}
	} else
		mySwitch.send(line);
}

void inbyte(int inchar) {
	static char inbuf[64];
	static int pos=0;
	if (inchar == '\r' || pos == 64) {
		inbuf[pos]=0;
		inlineProcess(inbuf);
		pos=0;
	} else if (inchar < ' ') {
		switch (inchar) {
			case 0x2: //ctrl-b
				mode=BINARY;
				break;
			case 0x17: //ctrl-W
				mode=SWITCH;
				break;
		}
	} else
		inbuf[pos++]=inchar;
}

void loop() {
  if (mySwitch.available()) {
		incodeProcess(mySwitch.getReceivedValue());
		mySwitch.resetAvailable();
	}
	while (Serial.available()) {
		inbyte(Serial.read());
	}
}

When the sketch has been compiled and loaded it is possible to interact with it using the "Serial Monitor" of the Arduino IDE or a terminal emulator. (my favuorite is screen). Set it to 115200 baud, end of line=CR.

The command for screen is simply

screen /dev/ttyUSB0 115200

I have set up the dip switches of the remote to the system code '11111' and the socket to system code '11111', unit code '00010' (it is operated by the D buttons of the remote)

'

Now when I push a button of the remote I get a line like the following:

11111 10000 1
11111 10000 0
11111 01000 1
11111 01000 0
11111 00100 1
11111 00100 0
11111 00010 1
11111 00010 0

The first group of 5 bits is the code of the remote (it is the configuration of the 5 switches hidden in the battery compartment of the remote. The second group is the letter A=10000, B=01000, C=00100, D=00010 (maybe other remotes have a fifth button). The final bit is ON (1) or OFF (1).

So I can use the remote to activate any process, just by checking the pattern received.

viceversa if I type in the code of my socket in the terminal emulator followed by 1 or 0 return (CR) the trasmitter sends the code. Please note that the sketch does not echo what is typed in. When I type:

11111 00010 1

nothing appears on the terminal but the socket gets switched on, and

11111 00010 0

switches it off.

The sketch has been designed to use arduino as a device of a host computer. A daemon could parse the input lines (commands from remote controls) and trigger actions when required by the configuration. The same demon can also write the code of a socket to turn on of off as in the example above. Given this idea of usage, echoing the input would be inconsistent: the demon would receive its own commands, too.