i2cdetect

Hi, I'm using an adapted version of i2cdetect for my own i2c experiments. Maybe it is useful for somebody else:

function scanI2c( i2c, first, last ) {
   if (typeof first === "undefined") {
        first = 0x03;
    }
    if (typeof (last) === "undefined") {
        last = 0x77;
    }
    print( "     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f" );
    for (var upper = 0; upper < 8; ++upper) {
        var line = upper + "0: ";

        for (var lower = 0; lower < 16; ++lower) {
            var address = (upper << 4) + lower;

            // Skip unwanted addresses
            if ((address < first) || (address > last)) {
                line += "   ";
                continue;
            }

            try {
                i2c.readFrom( address, 1 );
                line += (address + 0x100).toString( 16 ).substr( -2 );
                line += " ";
            } catch (err) {
                line += "-- ";
            }
        }
        print( line );
    }
}

// Usage
I2C1.setup( {scl: B8, sda: B9} );
scanI2c( I2C1, 0x03, 0x2f );

Output - first line is not aligned correctly.

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          03 04 05 06 07 -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

What would be the right place for such a code snippet?

1. Too special → don't share
   
2. Own module: require("i2cdetect").scan()
   
3. https://gist.github.com/
   
4. ???
   
   

It takes quite a long time to scan all addresses. Is it possible to decrease the timeout somehow?

That's great! I'm not sure - maybe a tutorial for the website, like 'Detecting I2C devices'?

I'm afraid that right now the I2C timeout isn't configurable - although I can't really see a reason why it shouldn't be smaller. Even a 50ms timeout should really be more than enough.

Yeah, I agree about the timeout. Does anyone know of any I2C devices that don't respond practically instantly? I can't think of any examples - though it'd be nice to be able to set the timeout, I think in the short term, it would be an improvement to just make it shorter.

on ESP you can use this with the latest build

I2C1.setup({sda: D4, scl: D5} );

function isDeviceOnBus(i2c, addr) {
  try {  
    return i2c.readFrom(addr,1);
  } 
  catch(err) { 
    return -1;
  }
}

function i2cdetect( i2c, first, last ) {
  if (typeof first === "undefined") first = 0x03;
  if (typeof (last) === "undefined") last = 0x77;

  print( "     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f" );
  for (var upper = 0; upper < 8; ++upper) {
    var line = upper + "0: ";
    for (var lower = 0; lower < 16; ++lower) {
      var address = (upper << 4) + lower;
      // Skip unwanted addresses
      if ((address < first) || (address > last)) {
        line += "   ";
        continue;
      }
      if ( ! isDeviceOnBus(i2c,address) ){
        line += (address + 0x100).toString( 16 ).substr( -2 )+" ";
      } else 
        line += "-- ";
    }
    print( line );
  }
}

i2cdetect( I2C1, 0x03, 0x77);

/* sample output for  a connected PCA9635 

     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: 60 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: 70 -- -- -- -- -- -- --

*/

now using a version that returns an array of ids

var isDevice = function isDeviceOnBus(i2cBus,id) {
      try {
          return i2cBus.readFrom(id,1);
      }
      catch(err) {
          return -1;
      }
};

var detect = function(i2c,first, last) {
      first = first | 0;
      last = last | 0x77;
      var idsOnBus = Array();
      for (var id = first; id < last; id++) {
          if ( ! isDevice(i2c,id) ) {
              idsOnBus.push(id);
          }
      }
      return idsOnBus;
};


I2C1.setup({sda: D4, scl: D5} );
console.log(detect(I2C1));

On ESP you have to add pinMode for the I2C pins when using sdk 2.0

I2C1.setup({sda: D4, scl: D5} );
pinMode(D4,"opendrain");
pinMode(D5,"opendrain");

Not needed - don't know what went wrong....

changes:

• include last id in scan
  
• change if clause
  

• add I2C1.setup() sample for Espruino boards

  function isDeviceOnBus(i2c,id) {
    try {
      return i2c.readFrom(id,1);
    }
    catch(err) {
      return -1;
    }
  }
  
  function detect(i2c,first, last) {
    first = first | 0;
    last = last | 0x77;
    var idsOnBus = Array();
    for (var id = first; id <= last; id++) {
      if ( isDeviceOnBus(i2c,id) != -1) {
        idsOnBus.push(id);
      }
    }
    return idsOnBus;
  }
  
  // Espruino boards
  // I2C1.setup( {scl: B8, sda: B9} );
  
  // ESP8266 
  I2C1.setup({sda: D2, scl: D4} );
  
  console.log('I2C detect as array:',detect(I2C1));
  
  

Thanks for this code. I added console.log and LED blink inside the loop, to convince myself it had not hung. The slowness is a drag. Eventually I discovered that the i2c device I was using actually had its address documented. https://learn.adafruit.com/adafruit-i2c-qt-rotary-encoder