The TSOP SM0038 is an IR receiver on the InduinoX. The TSOP will help you to interface your TV remote with the InduinoX and in the Process learn the basics of Wireless Communication. The TSOP is connected to pin digital 15(Analog 1).
The TSOP outputs a constant HIGH signal when idle and as it receives data, it tends to invert the data. i.e when an IR LED is transmitting data onto the TSOP, everytime the IR led goes high, the TSOP will go LOW and vice versa. Remote control signals are often bytes of data that is encoded and transmitted by pulsing(switching ON & OFF the IR LED at a specific frequency) Most TV remote controls work at 32-40 Khz frequency and most receivers can receive this range.
Heres a link to a nice write up on different remote control protocols. lets first take a look how the Sony Remote Control Protocol Works. We stick to Sony as it is the easiest one to get started with. Read this before proceeding
Here's a basic outline of how the data is sent. Every time you press a button on a Sony remote control, it sends out a 13Bit data. The first bit is a start bit indicating there are 12 bits of data following it. The next 7 bits are the command bit which will vary depending upon the keys being pressed. The last 5 bits are the address bits which will the same for all buttons but vary for remote controls of different devices.
The black bars in the following image correspond to high signals (called marks) and the white spaces in between correspond to low signals (called spaces). The duration of the 'marks' varies according to the bit being transmitted. It is 2.4ms for the start bit, 1.2ms for HIGH bit and 0.6ms for LOW bit. The duration of the 'spaces' is a constant 0.6ms. Every mark is followed by a space. Any data can be converted to binary format and transmitted in this manner. In fact this is the basic form of all types of serial communication.
Technique to decode this signal train, would be to constantly monitor the TSOP pin[Digital 15] for its normal state and the moment it produces a low signal, measure the duration of the low signal. If the measured duration of the low signal is around 2ms then measure and store the duration for the next 12 bits of the incoming data. After storing the data, evaluate the duration and based on the duration convert the data to decimal / hexadecimal and use it in your application.
The duration of a signal on an input pin of the arduino can be measured using the pulseIn function. Read more about this function here
There is an interesting IR remote library that can help you read different remotes without any difficulty. It can also generate different remote signals. However currently it can generate these signals only on the 3rd pin of the Arduino / InduinoX (PWM pin). Incase you want to use this library to generate remote control signals, we advise that you put the jumpers of the RGB LED OFF and connect a wire between the 3rd pin and the Analog 0 of the InduinoX. The IR LED on the InduinoX is connected to Analog 0(a.k.a digital 14)
You can download the IR remote library and other libraries, sample codes for the InduinoX here -> Click Here to Download InduinoX Sample Codes & Required Libraries[Right Click & use Save As]
How to use Libraries in Arduino - An Overview
To use any library you download, unzip the downloaded file and copy its contents to the libraries folder inside your arduino directory. You can check the library by opening the arduino ide and going to Sketch -> Import Library Option, if your library is in the proper location, it will show up here. Next if there is an example provided with the library (it will be inside a folder called example inside the base folder of the library) it will show up under the libraries name in the File->Examples Menu. You should reopen Arduino for the library to show up.
Once you install the IRremote, You can try the example program, IRrecvDemo. This program will give you a serial output of the HEX code for each value corresponding to each button on a remote. We will be using the decimal value in our next program. To get the decimal value, just do the following modification
replace this line
with
Serial.println(results.value);
Ensure the TSOP jumper is ON!
Here's a video of a simple project - A remote control interface for our Binary Counter.
Here's the source code for the same
/*
This sketch increases a 3 bit number every time '+' button is pressed and decreases the value when '-' button is pressed on the remote.It shows the output on 3 LEDs in Binary Format
*/
#include <IRremote.h>
int RECV_PIN = 15;
IRrecv irrecv(RECV_PIN);
decode_results results;
int i = 0;
void setup()
{
pinMode(11,OUTPUT); // declare LED pins as output pins
pinMode(12,OUTPUT);
pinMode(13,OUTPUT);
pinMode(7,INPUT);// Declare the 7th pin as a input pin. We will use the button on the 7th pin
digitalWrite(7,HIGH);
irrecv.enableIRIn(); // Start the Remote receiver
Serial.begin(9600);
}
void loop()
{
if (irrecv.decode(&results)) {
Serial.println(results.value);
switch(results.value) // if the '+' button is pressed
{
case 2320:
i=0;
break;// 2320 is the value for '0'
case 16:
i=1;
break;// 16 is the value for '1'
case 2064:
i=2;
break;// 2064 is the value for '2'
case 1040:
i=3;
break;// 1040 is the value for '3'
case 3088:
i=4;
break;// 3088 is the value for '4'
case 528:
i=5;
break;// 528 is the value for '5'
case 2576:
i=6;
break;// 2576 is the value for '6'
case 1552:
i=7;
break;// 1552 is the value for '7'
case 1168: // this is the value for the increment button
if(i<7) // if counter value is less than 7 or 3 bits
i++; // increment counter value
else
i=0;
break;
case 3216: // this is the value for the decrement button
if(i>0) // if counter value is greater than 0 or 3 bits
i--; // decrement counter value
else
i=7; // reset counter to 7
break;
}
int a=i%2; // calculate LSB
int b=i/2 %2; // calculate middle bit
int c=i/4 %2; // calculate MSB
digitalWrite(11,c); // write MSB
digitalWrite(12,b); // write middle bit
digitalWrite(13,a); // write LSB
while(digitalRead(7)==0); // wait till button is released to avoid incrementing the counter again
delay(300); // small delay to avoid debounce
irrecv.resume(); // Receive the next value
}
}
