iOS IR Remote with Arduino

Basically, how remote controllers work is, the buttons on the control panel will trigger a certain command, and the microcontroller on the board will code the command in binary format, then controls the infrared LED to blink in a certain way according to the code. On any device you want to control, the infrared receiver will catch the signal and decode command, so that the device knows what it needs to do.

The structure will be the same if we want to make it for smartphones. The smartphone needs to be able to encode a command and control a infrared LED to blink. Since there’s no direct access from the phone to the LED, so we need a microcontroller to listen to input from the smartphone, and blink the LED accordingly. In order to be compatible with almost all smartphones, including iPhone and Android, we choose headphone jack as the interface between the phone and the microcontroller. This means we will use audio signal to represent the command, which the microcontroller will not be able to read directly. In this case, we need a soft modem to do the translation.

Hardwares :

• Arduino Uno x 1 (as the microcontroller)
• Soft modem x 1
• IR LED x 1
• Arduino breadboard shield x 1(just for cleaner prototyping)
• Headphone wire x 1

Hardware setup

Connect soft modem to Uno, and connect the breadboard shield on top of them, then connect the IR LED to Uno’s PWM pin 3 via breadboard. Finally, connect the soft modem and the iPhone with the headphone wire. Done.

Arduino coding

Arduino Uno has to take care of the LED blinking, and also listen to soft modem input. When dealing with the soft modem input, the coded command can be several byte in size, so need to buffer the input data to get the complete command. We used 3 libraries in our codes to do IR control(IRremote), soft modem listening(SoftModem) and buffering(ByteBuffer).In the steup function, we need to initialize the buffer and soft modem.void setup() { Serial.begin(9600); // Initialize the buffer with a capacity for 4 bytes buffer.init(4); delay(1000); modem.begin(); }In the loop function, Arduino will keep listening to the soft modem. While soft modem is available, we read 2 bytes from the soft modem. Then check if we need to clear the buffer. If not, we put the 2 bytes into the buffer. This is how we get the command from soft modem. When we get the command, we simply use a IRsend to send the command to the IR LED under NEC Protocol.void loop() { while(modem.available()){ int c = modem.read(); if((buffer.getSize() == 4 || buffer.getSize() == 0) && c == 0xFF) { buffer.clear(); } else { buffer.put(c); } } if(buffer.getSize() == 4) { long cmd = buffer.getLong(); Serial.print("Sending cmd: "); Serial.println(cmd, HEX); irsend.sendNEC(cmd, 32); // NEC Protocol command delay(100); }There’s one issue we encountered when we ran the code. Both IRremote and SoftModem library are using timer2, so we had to uncommented line 61 in IRremoteInt.h to resolve the conflict.

iOS App

We have 2 buttons on the main view, and each button represents a command. We also have an info view, in which you can change the command for both buttons. Once the button is pressed, we will use a serial generator to encode a audio signal representing the command, and the signal will be received by the soft modem.- (void)buttonPressed:(UIButton*)button { NSString* buttonKey = (button.tag == 1) ? @"first" : @"second"; NSString* hex = [[NSUserDefaults standardUserDefaults] stringForKey:buttonKey]; hex = [hex substringFromIndex:2]; NSData* hexData = [hex hexToBytes]; //NSLog(@"%@", hex); //NSLog(@"%@", [hex hexToBytes]); [APP_DELEGATE.generator writeByte:0xff]; [APP_DELEGATE.generator writeBytes:[hexData bytes] length:hexData.length]; }