Detecting an IR Beam Break with the Arduino IR Library

One reader asked how to use my Arduino Infrared Library to detect breakage of an IR beam. The answer was too long for the comments section, so I've extended into a blog post. One straightforward way is to use the library to modulate an IR LED at 38kHz, and use a standard IR detector module to detect the signal. The output from the module can be simply read as a digital input.

Here is a simple sketch to do that. The IR LED is connected to pin 3 through a 100 ohm resistor, the detector is connected to pin 2, and a status LED is connected to pin 13 (if your Arduino board doesn't have it already.) To create the modulated output, simply call irsend.enableIROut(38); to set the PWM to 38kHz, and then irsend.mark(0) to send a mark (i.e. turn the output on). The loop simply reads the input from the detector, inverts it (since the detector is active-low), and writes it to the status LED.

#include <IRremote.h>

#define PIN_IR 3
#define PIN_DETECT 2
#define PIN_STATUS 13

IRsend irsend;
void setup()
{
  pinMode(PIN_DETECT, INPUT);
  pinMode(PIN_STATUS, OUTPUT);
  irsend.enableIROut(38);
  irsend.mark(0);
}

void loop() {
  digitalWrite(PIN_STATUS, !digitalRead(PIN_DETECT));
}

You should see the pin 13 LED light up when the IR receiver detects an infrared signal, and go dark when the receiver does not detect an infrared signal. The circuit is basically trivial, but there's a schematic at my original article if you need one. The following picture shows the detector setup. Note the illuminated status LED.

If the circuit doesn't work, first use a cell phone camera to verify that the infrared LED is lit. If the LED is not lit, try reversing it. Here's my cellphone's view of the illuminated LED:

Next, point a TV remote control at the detector and make sure the status LED flashes. If the status LED doesn't come on, make sure you wired the detector properly, and connected to input 2 of the Arduino. If the status LED won't turn off when you break the beam, you probably aren't blocking the IR signal well enough. The detector is very sensitive, and IR bounces off many things, so you may need to separate the LED and detector by several feet and make sure you're fully blocking the IR beam. Note that the library assumes you're using a ATmega168/328, so you're on your own if you have a different processor.

The tricky part of this is the optics - figuring out how to set up the LED and receiver so the beam gets interrupted when you want it to. Also, you'll probably want to modify the detection logic to do something more interesting than just set the status LED, but that's left as an exercise for the reader :-)

Fixing my Concertmate MG-1 Synth

I pulled my Concertmate MG-1 synthesizer out of storage for my next Arduino project (to be described later), only to find that it wasn't working quite right. This posting briefly describes how I fixed it, in case anyone else has a similar problem.

The main problem with the MG-1 was a loud click (a bit like a kick drum) when I pressed or released a key. It sounded suspiciously like a DC signal being applied to a speaker. The second problem was that when I set the contour for an attack and decay, the note got louder and softer, but as the note got softer it was replaced with a buzz at the frequency of oscillator 1.

Conveniently, the Service Manual is available online. I studied it and the schematic, and my first guess was that there was a DC offset going into the CA3080 amplifier, resulting in an amplified DC signal in the output. The CA3080 is not a normal amplifier but an operational transconductance amplifier, an unusual amplifier where the current on a control input controls the amplification of the input signal (more info). In this case, it is used as a voltage-controlled amplifier, allowing the contour signal to control the output.

In the schematic below, op-amps U10A and U10B feed the differential output signal into the 38080 amplifier. Pin 5 of the 3080 receives the contour signal to provide the attack and decay when you press a key. This signal controls how much the inputs are amplified. The output goes into the master volume control, and then to the synthesizer outputs. If there's a DC offset between the input pins 2 and 3, there will be an amplified DC offset at the output.

Fortunately, there is a VCA Balance Trim adjustment to trim any DC offset, and the manual describes how to adjust this. I opened up the MG-1 and adjusted this, but unfortunately it made no difference at all.

Next, I stared at the schematic for the contour generator that feeds into the CA3080 amplifier, but couldn't see how that could be going wrong. I measured the inputs to the CA3080 with an oscilloscope and found they all seemed normal. However, the output showed a 3.75V DC jump when the key turned on, which explained the click. In addition, the contour input showed it was picking up some crosstalk from the oscillator 1 trace that runs next to it, and this was being amplified into the buzzing noise.

All signs pointed to a problem with the CA3080 amplifier chip, which was somehow amplifying a big DC signal. Unfortunately, the CA3080 is no longer being manufactured and is hard to obtain. Fortunately, by some bizarre twist of fate, I happened to have one in my rather small box of parts.

The picture below shows the two main circuit boards. The upper board is the sound generation, filtering, and amplification, while the lower board has the power supply, keyboard, control, and polyphonic sound.

I removed the circuit board, soldered in the new CA3080, got the switches centered just right so the circuit board could be replaced, and put it back together. Unfortunately, I didn't get any output at all. I was afraid I'd somehow destroyed my rare CA3080 chip, but fortunately discovered that if the switches are in intermediate positions, you don't get any signal. I returned the switches to their proper positions and all was well.

In conclusion, I succeeded in fixing my MG-1 and getting that lovely, rich Moog sound.

Don't walk! Controlling a pedestrian sign with an Arduino

My latest project is controlling a pedestrian sign with an Arduino, so it will automatically step through the states of walk, flashing don't walk, and solid don't walk. In addition, I added infrared remote control support so I can use a remote control to turn the sign on and off, set it to a particular state, or start the cycle.

The hardware

The pedestrian sign is controlled by two relays that switch 120-volt AC on and off; one powers the "walk" part of the sign, and one powers the "don't walk" part.

The Arduino drives the relays through transistors connected to 9-volt supply. Technically the relays are 12-volt relays, but they seem to work with 9 volts. I used one 10A relay, and one 5A relay, just because that's what I had around.

Needless to say, 120 volts can be dangerous, both to yourself and to your Arduino. Follow the appropriate precautions. I make no claims about the safety of this circuit.

The remote control input uses an IR detector module connected to the Arduino. For details on the IR detection, see the article on my IRremote library. The code section below describes how to modify the code to support different remotes.

I found the IR detector didn't work super-reliably when the sign was turned on. This was probably due to high-frequency electrical interference since adding some capacitors helped, but the light itself could have been interfering. I probably should have wired up the relay circuit and the IR detector circuit farther apart to minimize interference, as I did when controlling a DC motor.

Inside the pedestrian sign

You may be curious about what's inside a pedestrian sign. What I have is the lighting unit; this goes inside the metal case that you see attached to a traffic pole. (In case you're worried, I didn't steal this from an intersection. I got it on ebay from some city that was replacing their units with more efficient LED units.)

Inside the signal are two neon tubes, roughly the shape of the hand and the pedestrian; generating red and white light respectively. I use "neon tube" in the generic sense; I don't know what gas is actually inside. Note that the tubes are not colored and the cover is clear; the red color is entirely from the gas discharge.

Beneath the tubes are two high-voltage driver circuits, one for each tube. Each driver circuit runs off 120V AC and has an oscillator (using a LM2903 comparator) driving a flyback transformer through a power transistor (under the board). This generates multi-kilovolts to drive the tubes. Note at the far left the standoffs that keep the output wire an inch above the circuit board due to the high voltage. Needless to say, I stay away from the circuitry while it is operating. Each driver board has a separate AC input; when AC is fed in, the tube lights up. One drawback of the driver circuitry is it makes a high-pitched whine when turned on. I originally planned to use the sign to indicate unittest pass/fail status, but it was too annoying to people nearby.

The code

The Arduino code is available at IRtraffic.pde and has two main functions: IR processing and light cycle processing.

In the IR code, the IR remote is used to select one of five states: walk illuminated, blinking don't walk, don't walk illuminated, off, or cycling (which goes through the first three states). The IR functionality uses my IRremote library to decode the output from a remote control.

The code has the values for a particular remote control hard-coded. I used a Sony DVD remote:

#define OFF_CODE 0x1CB92 // Stop on Sony DVD remote
#define WALK_CODE 0xB92 // 1 on Sony DVD remote
#define BLINK_CODE 0x80b92 // 2 on Sony DVD remote
#define DONT_CODE 0x40b92 // 3 on Sony DVD remote
#define CYCLE_CODE 0x4CB92 // Play on Sony DVD remote

The first part of the loop function calls the IR library to see if an IR signal has been decoded. If so, it switches to the appropriate mode. If an unexpected IR value is encountered, it is printed to the serial port.

void loop() {
  // Process the IR input, if any
  if (irrecv.decode(&results)) {
    if (results.value == WALK_CODE) {
      Serial.write("Walk\n");
      mode = MODE_WALK;
      cycle = false;
    } 
    else if (results.value == DONT_CODE) {
      Serial.write("Don't walk\n");
      mode = MODE_DONT;
      cycle = false;
    } 
    else if (results.value == OFF_CODE) {
      Serial.write("Off\n");
      mode = MODE_OFF;
      cycle = false;
    } 
    else if (results.value == BLINK_CODE) {
      Serial.write("Blinking don't walk\n");
      mode = MODE_BLINK;
      blinkOn = true;
      nextBlinkMillis = millis() + 500; // 500 ms blink
      cycle = false;
    } 
    else if (results.value == CYCLE_CODE) {
      Serial.write("Cycle\n");
      nextCycleMillis =  millis() + 5000; // delay 5 seconds
      cycle = true;
      mode = MODE_WALK;
    } 
    else {
      Serial.print("unexpected value: ");
      Serial.println(results.value, HEX);
    }
    irrecv.resume(); // Resume decoding (necessary!)
  }

If you want to use a different remote, simply look at the "unexpected values" printed to the serial port while pressing the desired buttons, copy the hex values into the code, recompile, and reinstall. For instance, to use some Tivo buttons, simply change the button definitions to:

#define OFF_CODE 0x20df10ef
#define WALK_CODE 0xa10cd00f
#define BLINK_CODE 0xa10c8807
#define DONT_CODE  0xa10cc807
#define CYCLE_CODE 0xa10c6c03

The other main function of the code is timing. There are two timing cycles going on. First, if cycle mode is enabled, the mode is advanced through walk, blink, and don't walk every five seconds. Second, if in the blinking don't walk phase, the output is turned on or off every half second.

I originally used delays of 500 or 1000 ms for the timing, but this had the disadvantage that the light wasn't very responsive to the remote control - it would wait up to 1 second before processing the remote control value. I rewrote the code using the BlinkWithoutDelay approach. In this approach, there are no delays in the loop code. Instead, the millis() value is checked to see if it is time to change state. If nothing needs to be done, loop() ends without any delay.

In more detail, the boolean cycle is true if the light is to cycle between the three phases. In this case, nextCycleMillis is set to the time at which we move to the next cycle (i.e. 5 seconds in the future). Once we reach that time, the mode is advanced. The boolean blinkOn keeps track of whether the don't walk sign is on or off while blinking.

  if (cycle && millis() >= nextCycleMillis) {
    if (mode == MODE_WALK) {
      mode = MODE_BLINK;
      blinkOn = false;
      nextBlinkMillis = millis() + 500; // 500 ms blink
      nextCycleMillis = millis() + 5000; // delay 5 seconds
    } 
    else if (mode == MODE_BLINK) {
      mode = MODE_DONT;
      nextCycleMillis =  millis() + 5000; // delay 5 seconds
    } 
    else {
      mode = MODE_WALK;
      nextCycleMillis =  millis() + 5000; // delay 5 seconds
    }
  }

The other independent time is nextBlinkMillis. This is the time at which the don't walk sign should change state, and it is set 500ms into the future.

  if (mode == MODE_BLINK && millis() >= nextBlinkMillis) {
    blinkOn = !blinkOn;
    nextBlinkMillis = millis() + 500; // 500 ms blink
  }

The code may be confusing at first due to the two independent times (nextCycleMillis and nextBlinkMillis) and state variables (mode and blinkOn). It seemed simpler this way rather than folding both cycles into one.

Finally, the code sets the appropriate lights on or off:

  if (mode == MODE_WALK) {
    digitalWrite(DONT_PIN, LOW);
    digitalWrite(WALK_PIN, HIGH);
  } 
  else if (mode == MODE_DONT || (mode == MODE_BLINK && blinkOn)) {
    digitalWrite(DONT_PIN, HIGH);
    digitalWrite(WALK_PIN, LOW);
  } 
  else {
    digitalWrite(DONT_PIN, LOW);
    digitalWrite(WALK_PIN, LOW);
  } 

Conclusion

I have two extra pedestrian signs; I'll give them away for free if you can pick them up in the SF Bay Area.

Using arbitrary remotes with the Arduino IRremote library

My IRremote library decodes output from many infrared remotes: Sony, NEC, RC5, and RC6. However, many remotes use other protocols. While it's not too hard to add support for other protocols, I wanted to show how the library can be used with arbitrary remote controls.

This post describes a simple routine that will generate a unique code for each key on an arbitrary remote. The demo application flashes the LED the appropriate number of times when I push the 0-9 button on my remote.

How it works

The IRremote library records the duration of each (modulated) pulse sent by the remote control. Each key on the remote corresponds to a particular code value, which is converted to a particular sequence of pulses. If you know the encoding algorithm, you can determine the code value, and thus the key pressed. However, for many applications it doesn't really matter what the original code value is, as long as you can uniquely distinguish each key. Thus, if you can turn each unique sequence of pulses into a unique value, then this value will indicate the desired key.

To do this, I look at the duration of successive pulses. If the pulse is shorter than the previous, I assign 0. If the pulse is the same length, I assign 1. If the pulse is longer, I assign 2. (I compare on-durations with on-durations and off-durations with off-duations.) The result is a sequence of 0's, 1's, and 2's. I hash these values into a 32-bit hash value.

With luck, the 32-bit hash value will be unique for each key. Note that these hash values are arbitrary, and don't have any obvious connection with the underlying code value. Most encoding protocols use two different durations, so comparing shorter vs longer will work, but you can imagine a code with multiple duration values that wouldn't work here. In addition, hash collisions could occur, but are pretty unlikely with a 32-bit hash.

Code

The code can be downloaded from IRhashcode.pde. The sample application prints the "real" decoded value and the hash value. The "real" value will only work for supported protocols (Sony, RC5, RC6, NEC), but the hash value should work for almost any remote control.

The code is pretty straightforward. compare() compares the two measured durations within the 20% tolerance.

int compare(unsigned int oldval, unsigned int newval) {
  if (newval < oldval * .8) {
    return 0;
  } 
  else if (oldval < newval * .8) {
    return 2;
  } 
  else {
    return 1;
  }
}

The actual decoding is fairly simple. results->rawbuf holds the measured durations as space, mark, space, mark, ... The loop compares each duration with the next of the same type, and adds that value to the hash result.

#define FNV_PRIME_32 16777619
#define FNV_BASIS_32 2166136261
unsigned long decodeHash(decode_results *results) {
  unsigned long hash = FNV_BASIS_32;
  for (int i = 1; i+2 < results->rawlen; i++) {
    int value =  compare(results->rawbuf[i], results->rawbuf[i+2]);
    // Add value into the hash
    hash = (hash * FNV_PRIME_32) ^ value;
  }
  return hash;
}

The mystery FNV numbers come from the FNV 32-bit hash function, which combines all the values into a single 32-bit value.

The following example code prints out the "real" decoded value and the hash decoded value to the serial port. You will want to use this code to figure out what hash value is associated with each key on the remote.

void loop() {
  if (irrecv.decode(&results)) {
    Serial.print("'real' decode: ");
    Serial.print(results.value, HEX);
    Serial.print(", hash decode: ");
    Serial.println(decodeHash(&results), HEX);
    irrecv.resume(); // Resume decoding (necessary!)
  }
}

Here's a slightly more realistic example. It receives a code from a Philips remote and flashes the LED appropriately. If you press "1", it flashes once, if you press "8" it flashes 8 times, etc. The code simply uses a case statement to match against the pressed key, and blinks that many times.

You will need to modify this to work with your remote. If it doesn't recognize the code, it will print it to the serial output. Put these unrecognized values into the code to make it work with your remote.

#define LEDPIN 13
void blink() {
  digitalWrite(LEDPIN, HIGH);
  delay(200);
  digitalWrite(LEDPIN, LOW);
  delay(200);
}  

void loop() {
  if (irrecv.decode(&results)) {
    unsigned long hash = decodeHash(&results);
    switch (hash) {
    case 0x322ddc47: // 0 (10)
      blink(); // fallthrough
    case 0xdb78c103: // 9
      blink();
    case 0xab57dd3b: // 8
      blink();
    case 0x715cc13f: // 7
      blink();
    case 0xdc685a5f: // 6
      blink();
    case 0x85b33f1b: // 5
      blink();
    case 0x4ff51b3f: // 4
      blink();
    case 0x15f9ff43: // 3
      blink();
    case 0x2e81ea9b: // 2
      blink();
    case 0x260a8662: // 1
      blink();
      break;
    default:
      Serial.print("Unknown ");
      Serial.println(hash, HEX);    
    }
    irrecv.resume(); // Resume decoding (necessary!)
  }
}

Debugging

The most likely problem is a key will occasionally have different code values. This is likely due to random errors in measuring the pulses. The code considers any durations within +/- 20% to be equal; you can try increasing this value.

If you're using a RC5/RC6 remote, each key will alternate between two different values. In that case, you probably want to use the "real" decoded value, rather than the hashed value, since you can mask out the toggle bit.

If your remote uses a protocol with multiple duration values, you probably won't get unique values from this algorithm.

For other problems, see the IRremote page, which also has a schematic for wiring up the IR detector.

Conclusion

This IR hash algorithm extends the IRremote library to be usable with many more types of infrared remote controls. Please let me know if you use it, and I'll add a link to your project if you want.

Arc beats Python for a web-controlled stereo

I recently set up a web interface to my stereo, implementing it in both Python and Arc. I found that, much to my surprise, writing the Arc implementation was much easier than the Python implementation in this case.

In my stereo controller system, I go to a web page that has an image of the appropriate remote control, and click the button. The Javascript in the web page sends a hex code back to the server, which sends the code to an Arduino microcontroller board, which converts the code into an infrared signal. The stereo interprets this signal as a command from the remote control and performs the desired action. It sounds complicated, but it responds quickly, even if I use the browser on my cell phone. I wrote up more details on the system earlier.

The web server for this project is fairly straightforward: it needs to serve some static HTML pages and images, and needs to receive POST messages and forward the data over the serial port to the Arduino. I originally wrote the code in Python:

import cgi
import serial

from BaseHTTPServer import HTTPServer
from SimpleHTTPServer import SimpleHTTPRequestHandler

class MyHandler(SimpleHTTPRequestHandler):
  def do_POST(self):
    if self.path == '/arduino':
      form = cgi.FieldStorage(fp=self.rfile, headers=self.headers,
        environ={'REQUEST_METHOD':'POST'})
      code = form['code'].value
      print 'Sent:', code
      arduino.write(code)
      self.send_response(200)
      self.send_header('Content-type', 'text/html')
      return
    return self.do_GET()

arduino = serial.Serial('/dev/ttyUSB0', 9600, timeout=2)
server = HTTPServer(('', 8080), MyHandler).serve_forever()

The Python web server is based on SimpleHTTPServer. To handle POST requests to the /arduino URL, I made a simple handler subclass that pulls the data out of the response, sends it to the serial port, and returns a blank response. The last two lines open the serial port and start up the server. The static web page serving comes "for free."

After writing this, I decided to try writing a version in Arc:

(= srvops* (table))

(= arduino-serial (outfile "/dev/ttyUSB0" 'binary))

(defopr || req "/index.html")

(defop arduino req (w/stdout (stderr)
  (let code (arg req "code")
    (write code arduino-serial)
    (prn "Sent code:" code))))

(thread (serve 8080))

Since you may not be familiar with the Arc web server, I'll give a brief explanation. The first line clears out the server's default pages (login, whoami, prompt, etc) that make sense for news.yc, but not for me. The next line opens the serial port. Next, the mysterious || redirects the home page. The next four lines are the handler for "/arduino": the "code" parameter is pulled out of the request (req). The code is written to the serial port, and printed to the log. The last line starts a serving thread on port 8080.

I'm not going to count tokens since that's a silly metric, but the Arc code is a clear winner here. The first Python disadvantage is the hideous cgi.FieldStorage call to parse the POST data; apparently this is the way to do it, but it took me considerable time to get this right. The second Python disadvantage is the necessity to set up the return code and content-type for the response. I ended up with a browser-specific bug when I didn't have this right, since some Javascript interpreters expect a particular response. Arc automatically sends a valid response. The main Arc disadvantage is there's no real serial port support; the Arc code just opens the port and hopes for the best. On the other hand, Python's serial library lets you set the baud rate, timeouts, and other parameters.

Arc and Python have a few more minor differences. Python requires imports, which Arc doesn't. Arc has the silly clearing of srvops* to avoid unwanted pages. Starting the server thread is simpler in Arc but not as flexible.

To summarize, I found the Python code difficult and error-prone to write, and the Arc code was shorter and just worked. This was a surprise to me; usually I find Python straightforward and Arc gives me pain when I have to write a bunch of code for some trivial thing it doesn't support. (For example, generating a time string in my temperature monitoring.) In this case, however, Arc came out ahead. Perhaps this is because Arc's flagship application is a web server, so it handles web serving well.

Obviously this is a fairly trivial program - the complexity is actually in the Javascript code and the C++ code on the Arduino - so I'm not claiming this as an overall victory for Arc over Python. But it's still interesting to find Arc came out ahead in this case.

TV-B-Gone for the Arduino

I've ported the TV-B-Gone code to run on the Arduino board. If you haven't seen a TV-B-Gone, it's a cute gadget that you point at a TV that's bothering you, and it turns the TV off. Internally, it's an infrared remote that broadcasts more than 100 different off codes that work on almost any TV. I figured it would be interesting to get the TV-B-Gone running on the Arduino.

Update (November 2010)

I have a new, improved version of the software. Details and download are here.

The software

I started with the TV-B-Gone firmware, which is available under Creative Commons license. The TV-B-Gone runs on an ATtiny85 microcontroller, not the ATmega328 used by the Arduino, so some porting was required. One tricky part of the port is the IR signals are generated using the low-level hardware timer for PWM (pulse-width modulation). Since the ATtiny85 runs at 8MHz, and the Arduino runs at 16MHz, the timing code needed to be re-written, both the 10us delay loop and the timer register operations. The quick summary is I'm using Timer 2, scaling the clock by 8, using OCR2A to control the frequency and OCR2B to control the duty cycle, and have output on pin 3 (OC2B). (You are not expected to understand this. See my article on Secrets of Arduino PWM for details of how these timers work.)

#define freq_to_timerval(x) (F_CPU / 8 / x - 1)
...
    pinMode(IRLED, OUTPUT);
    TCCR2A = _BV(COM2A0) | _BV(COM2B1) | _BV(WGM21) | _BV(WGM20);
    TCCR2B = _BV(WGM22) | _BV(CS21);
...
    OCR2A = freq; 
    OCR2B = freq / 3; // 33% duty cycle

Another tricky thing is the original firmware stores the IR codes in program space, not RAM. The microcontrollers use a Harvard architecture, which means they have separate memory and data paths for code and data, unlike normal processors that use a von Neumann architecture. Because RAM storage is so small on these microcontrollers, the IR codes are stored in program space, with the result you need to use special methods to access them, rather than normal C pointers. Program memory storage is indicated with the PROGMEM macro and pulled out of memory using special functions such as pgm_read_byte. This makes the code somewhat confusing, for example:

const struct IrCode *NApowerCodes[] PROGMEM = {
  &code_na000Code,
...
}

data_ptr = (PGM_P)pgm_read_word(NApowerCodes+i);  

The original firmware stores the codes as compressed indices into tables of durations. See the TV-B-Gone design for details. Unfortunately, the Arduino's compiler didn't like the zero-length array in the IrCode structure, so I needed to rewrite the long file of codes to include another level of indirection.

Apart from these factors, porting was straightforward, and I tried to keep the original code where possible. I ripped out all the power-up and watchdog code. I replaced the low-level serial code with the Arduino's Serial library. Finally, I packaged it up into an Arduino sketch, which you can download. (Update: get the improved version here.)

The hardware

The hardware is straightfoward. I use pin 13 for the status LED; some Arduinos conveniently have an LED already wired up. Pin 3 is the PWM output to the IR LED through a 100 ohm resistor. If you want more range, add a driver transistor and use multiple IR LEDs. Pin 0 (update: pin 5) selects North American or European codes; leave it unconnected for North America and ground it for European. Pin 1 (update: 2) is connected via a pushbutton to ground to trigger the code transmission. (Update: pins have changed in the new version.)

To use the Arduino TV-B-Gone, point the IR LED at your TV, push the button, and your TV should turn off when the circuit hits the right code, which could take up to a minute. The visible LED should flash for each code that is transmitted. If the circuit doesn't work, use a cellphone camera to verify that the IR LED is transmitting. Don't expect more than a few feet range unless you use a transistor to increase the power. The code will print debugging output to the serial port if you set DEBUG in main.h.

Summary

Is the Arduino TV-B-Gone practical? If you want a TV-B-Gone that you can carry around to amaze your friends, the kit or product is much more compact, has high-powered IR outputs for longer range, and is nicely packaged. However, the Arduino platform is convenient for experimenting, and many people already have it, so I expect people will find it interesting.

You might wonder why I'm not using my Arduino Infrared Library for this project. Actually, I plan to at some point, but I wanted to get the straightforward port working first. In addition, my library will need some extensions to support all the codes that the TV-B-Gone supports.

I hope you enjoy the Arduino TV-B-Gone, and remember to use it for good, not evil!

Controlling your stereo over the web with the Arduino infrared library

Here's how you can control your stereo over the web. Not only that, but any other electronics with a IR remote control can now be controlled through your browser. You can even use your smart phone's browser to control your stereo from across the room or around the world.

This project has several pieces: a simple Python web server running on your computer, an Arduino with my infrared library, and an IR LED or other emitter. The Python web server provides a web page with a graphical remote control. Clicking on the web page sends a code to the web server, which sends it over the serial port to the Arduino, which sends it to the IR LED, which controls your device.

The web server

I used a rather trivial Python web server (based on SimpleHTTPServer) that performs two tasks. First, it provides the static HTML pages and images. Second, it receives the POST requests and sends them to the Arduino using the pyserial library.

The following code excerpt shows the handler that processes POSTs to /arduino by extracting the code value out of the POST data and sending it to the Arduino over the serial line. The Python server automatically provides static pages out of the current directory by default; this is how the HTML files and images are served. The code assumes the serial port is /dev/ttyUSB0, which is typically the case on Linux.

class MyHandler(SimpleHTTPRequestHandler):
  def do_POST(self):
    if self.path == '/arduino':
      form = cgi.FieldStorage(fp=self.rfile, headers=self.headers,
        environ={'REQUEST_METHOD':'POST'})
      code = form['code'].value
      arduino.write(code)
      self.send_response(200)
      self.send_header('Content-type', 'text/html')
      return
    return self.do_GET()

arduino = serial.Serial('/dev/ttyUSB0', 9600, timeout=2)
server = HTTPServer(('', 8080), MyHandler).serve_forever()

The server can be accessed locally at http://localhost:8080. You may need to mess around with your firewall and router to access it externally; this is left as an exercise for the reader. I found that using my cell phone's browser via Wi-Fi worked surprisingly well, and over the cellular network there was just a slight lag (maybe 1/3 second).

The Arduino code

The code on the Arduino is pretty simple. It reads a command from the serial port and makes the appropriate IR library call. Commands consist of a character indicating the type of code, followed by 8 hex characters. For instance, "S0000004d1" sends the code 4d1 using Sony protocol; this is "play" on my Sony CD player. "N010e03fc" sends 010e03fc using NEC protocol; this turns my Harman Kardon stereo on. The full code is here, but some highlights:

void processSerialCode() {
  if (Serial.available() < 9) return;
  char type = Serial.read();
  unsigned long code = 0;
  // Read 8 hex characters into code (omitted)
  if (type == 'N') {
    irsend.sendNEC(code, 32);
  } 
  else if (type == 'S') {
    // Send Sony code 3 times
    irsend.sendSony(code, 12);
    delay(50);
    irsend.sendSony(code, 12);
    delay(50);
    irsend.sendSony(code, 12);
  }
  // More code for RC5 and RC6
}

In more detail, the Arduino waits for 9 characters to be available on the serial port. It then parses the hex value and calls the appropriate IR library send routine. The Arduino code does some special-case stuff for the different code types. Sony codes are transmitted three times as the protocol requires. The RC5 and RC6 protocol uses a toggle bit that is flipped on each transmission. (Disclaimer: I don't have RC5/RC6 devices, so this code is untested.) If your device uses a different protocol that the library doesn't support, you're out of luck unless you add the protocol to the library. That's probably not too hard; a couple people have already implemented new protocols.

The web page

Most of the smarts of the system are in the web page. In my setup, I have a HK-3370 stereo, and a Sony CDP-CE335 CD player. I took a picture of the remote for each and used an HTML image map to make each button clickable. Clicking on a button uses Ajax to POST the appropriate IR code to the server.

I use Ajax to send the code to the server to avoid reloading the web page on every click. The Javascript code is verbose but straightforward. The first part of the code creates the XML request object; unfortunately different browsers use different objects. The next part of the code creates and sends the POST request. The actual data sent to the server is, for instance, "code=N12345678" to send 0x12345678 using NEC protocol.

function button(value) {
  if (window.XMLHttpRequest) {
   request = new XMLHttpRequest();
  } else if (window.ActiveXObject) {
    try {
      request = new ActiveXObject("Msxml2.XMLHTTP");
    } catch (e) {
      try {
        request = new ActiveXObject("Microsoft.XMLHTTP");
      } catch (e) {}
    }
  }
  request.open('POST', '/arduino', true);
  request.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
  request.setRequestHeader('Content-length', value.length);
  request.setRequestHeader('Connection', 'close');
  request.send('code=' + value);
}

The clickable buttons are defined in the HTML through an image and an image map. Generating the image and the image map is the hard part of the whole project:

<img src="hk3370.png" width="268" height="800" border="0" usemap="#map" />
<map name="map">
<area shape="rect" coords="60,97,85,111" href="#" alt="on" onClick="button('N010e03fc')" />
<area shape="rect" coords="104,98,129,109" href="#" alt="off" onClick="button('N010ef906')" />
...

Each line in the map defines a region of the image as a button with a particular code. When clicked, this region will call the button function with the appropriate code, causing the code to be sent to the web server, the Arduino, and finally to the stereo. The alt text isn't actually used, but I recommend it to keep track of what button is associated with each line. The href causes the cursor to change when you go over the region, but isn't necessary.

In this approach, the Arduino code and web server code are very simple, as they don't need to know the functions of the codes. A different way to implement this system would be to put the table of codes ("SONY_CD_ON" = 4d1, etc.) either in the web server code or the Arduino code.

To generate the web pages, I took a picture of the remote with my camera and cleaned up the picture with GIMP. I used the GIMP image map plugin to create the image map. I outlined each button, then filled in the URL with the appropriate IR code, and filled in the alt text with the name of the button. Finally, I copied the map file into the HTML file and edited it to use the Javascript function.

The easiest way to obtain the IR codes is to use the IRrecvDump example sketch included in my IR library. Simply press the button on your remote, see what code was sent, and put that code into the image map. Alternatively, you may be able to find codes in the LIRC database.

Once you get going, it's actually fairly quick to generate the image map. Select a button in the editor, click the physical button on the remote, copy the displayed value into the editor, and move on to the next button. As long as you don't get obsessive and start tweaking the regions to line up perfectly, it's pretty quick.

If you don't want to mess around with the image map, take a look at simple.html. This file shows how to use standard HTML buttons. Not as cool as the image, but much easier:

<input type="button" value="on" onClick="button('N010e03fc')" >
<input type="button" value="off" onClick="button('N010ef906')" >
...

The hardware

The Arduino does the work of converting the hex code into an IR signal. The IR library uses digital PWM pin 3 as output, which must be connected to your IR emitter. I use a 100 ohm resistor to limit current. Wiring it up is trivial.

I used a Tivo IR blaster that I had lying around, but a plain IR LED will work too. The following picture shows an IR blaster attached to my sterero. Note that the blaster needs to be positioned about the stereo's IR receiver; it may be easier to see the receiver with a flashlight.

Putting it all together

To summarize the steps:

• Download the files and unpack them.
• Get the infrared library and install it.
• Aim the IR source at the device(s) to control, and connect it to the Arduino. (You may want to use a visible LED for testing.)
• Connect the Arduino to the computer's USB port.
• Compile and install IRwebremote.pde using the Arduino IDE.
• Create HTML files for your remote controls. (This is the hard step.)
• Run the Python server: python server.py
• Go to http://localhost:8080 and control the devices.

This project has multiple pieces and requires customization, so it's not a plug-and-play project. I only recommend trying this if you know what you're doing. Good luck!