PCA9544a 4-Channel I2C Mux

The 4 Channel I2C Multiplexer is basically a digital switch for up to 4 I2C devices. It uses a PCA9544A multiplexer IC to allow one of four devices to be connected to the I2C bus at one time, whilst disconnecting the other three. This is really useful for I2C devices that have a fixed I2C address.

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How To Connect

var Cylon = require("cylon");

Cylon.robot({
    connections: {
        raspi: {
            adaptor: 'raspi'
        }
    },

    devices: {
        pca9685: {
            driver: 'pca9685',
            connection: "raspi",
            address: "0x73"
        }
    },
});

How To Use

var cylon = require("cylon");

// We must use a mutex lock to ensure the mux state when reading values
var lock = new (require("rwlock"))();

// Mutex protected initialization
var getCoefficients = function(setChannel, bmp180) {
    return lock.writeLock("i2c1_0x73", function(release) {
      return setChannel(function() {
        return bmp180.readCoefficients(function(err) {
          if (err) {
            console.log(err);
          }
          return release();
        });
      });
    });
  };

// Mutex protected data read
var getMeasurement = function(index, setChannel, bmp180) {
    return lock.writeLock("i2c1_0x73", function(release) {
      return setChannel(function() {
        return bmp180.getPressure(1, function(err, val) {
          if (err) {
            console.log(err);
          } else {
            val.time = Math.floor(Date.now() / 1000);
            console.log(index + " " + JSON.stringify(val));
          }
          release();
          return;
        });
      });
    });
  };

var robot_config = {
    name: "test",
    connections: {
      raspi: {
        adaptor: "raspi"
      }
    },
    devices: {
      pca9544a: {
        driver: "pca9544a",
        connection: "raspi",
        address: "0x73"
      },
      bmp180_0: {
        driver: "bmp180",
        connection: "raspi",
        address: "0x77"
      },
      bmp180_1: {
        driver: "bmp180",
        connection: "raspi",
        address: "0x77"
      }
    },
    work: function(my) {
      /* The mux is in an unkown state at startup, so we mush re-read th
      *   coefficients with a mutex protected call to ensure valid data
      */
      getCoefficients(my.pca9544a.setChannel1, my.bmp180_1);
      getCoefficients(my.pca9544a.setChannel0, my.bmp180_0);
      return every(20..seconds(), function() {
        getMeasurement(1, my.pca9544a.setChannel1, my.bmp180_1);
        getMeasurement(0, my.pca9544a.setChannel0, my.bmp180_0);
        return;
      });
    }
  };

cylon.robot(robot_config);

cylon.start();