index.js

// javascript/node  rewrite of the Adafruit ads1x15 python library...
const i2c = require("i2c-bus");

// chip

const IC_ADS1015 = 0x00;
const IC_ADS1115 = 0x01;

// Pointer Register
const ADS1015_REG_POINTER_MASK = 0x03;
const ADS1015_REG_POINTER_CONVERT = 0x00;
const ADS1015_REG_POINTER_CONFIG = 0x01;
const ADS1015_REG_POINTER_LOWTHRESH = 0x02;
const ADS1015_REG_POINTER_HITHRESH = 0x03;

// Config Register
const ADS1015_REG_CONFIG_OS_MASK = 0x8000;
const ADS1015_REG_CONFIG_OS_SINGLE = 0x8000; // Write: Set to start a single-conversion
const ADS1015_REG_CONFIG_OS_BUSY = 0x0000; // Read: Bit = 0 when conversion is in progress
const ADS1015_REG_CONFIG_OS_NOTBUSY = 0x8000; // Read: Bit = 1 when device is not performing a conversion
const ADS1015_REG_CONFIG_MUX_MASK = 0x7000;
const ADS1015_REG_CONFIG_MUX_DIFF_0_1 = 0x0000; // Differential P = AIN0, N = AIN1 (default)
const ADS1015_REG_CONFIG_MUX_DIFF_0_3 = 0x1000; // Differential P = AIN0, N = AIN3
const ADS1015_REG_CONFIG_MUX_DIFF_1_3 = 0x2000; // Differential P = AIN1, N = AIN3
const ADS1015_REG_CONFIG_MUX_DIFF_2_3 = 0x3000; // Differential P = AIN2, N = AIN3
const ADS1015_REG_CONFIG_MUX_SINGLE_0 = 0x4000; // Single-ended AIN0
const ADS1015_REG_CONFIG_MUX_SINGLE_1 = 0x5000; // Single-ended AIN1
const ADS1015_REG_CONFIG_MUX_SINGLE_2 = 0x6000; // Single-ended AIN2
const ADS1015_REG_CONFIG_MUX_SINGLE_3 = 0x7000; // Single-ended AIN3
const ADS1015_REG_CONFIG_PGA_MASK = 0x0e00;
const ADS1015_REG_CONFIG_PGA_6_144V = 0x0000; // +/-6.144V range
const ADS1015_REG_CONFIG_PGA_4_096V = 0x0200; // +/-4.096V range
const ADS1015_REG_CONFIG_PGA_2_048V = 0x0400; // +/-2.048V range (default)
const ADS1015_REG_CONFIG_PGA_1_024V = 0x0600; // +/-1.024V range
const ADS1015_REG_CONFIG_PGA_0_512V = 0x0800; // +/-0.512V range
const ADS1015_REG_CONFIG_PGA_0_256V = 0x0a00; // +/-0.256V range
const ADS1015_REG_CONFIG_MODE_MASK = 0x0100;
const ADS1015_REG_CONFIG_MODE_CONTIN = 0x0000; // Continuous conversion mode
const ADS1015_REG_CONFIG_MODE_SINGLE = 0x0100; // Power-down single-shot mode (default)
const ADS1015_REG_CONFIG_DR_MASK = 0x00e0;
const ADS1015_REG_CONFIG_DR_128SPS = 0x0000; // 128 samples per second
const ADS1015_REG_CONFIG_DR_250SPS = 0x0020; // 250 samples per second
const ADS1015_REG_CONFIG_DR_490SPS = 0x0040; // 490 samples per second
const ADS1015_REG_CONFIG_DR_920SPS = 0x0060; // 920 samples per second
const ADS1015_REG_CONFIG_DR_1600SPS = 0x0080; // 1600 samples per second (default)
const ADS1015_REG_CONFIG_DR_2400SPS = 0x00a0; // 2400 samples per second
const ADS1015_REG_CONFIG_DR_3300SPS = 0x00c0; // 3300 samples per second (also 0x00E0)
const ADS1115_REG_CONFIG_DR_8SPS = 0x0000; // 8 samples per second
const ADS1115_REG_CONFIG_DR_16SPS = 0x0020; // 16 samples per second
const ADS1115_REG_CONFIG_DR_32SPS = 0x0040; // 32 samples per second
const ADS1115_REG_CONFIG_DR_64SPS = 0x0060; // 64 samples per second
const ADS1115_REG_CONFIG_DR_128SPS = 0x0080; // 128 samples per second
const ADS1115_REG_CONFIG_DR_250SPS = 0x00a0; // 250 samples per second (default)
const ADS1115_REG_CONFIG_DR_475SPS = 0x00c0; // 475 samples per second
const ADS1115_REG_CONFIG_DR_860SPS = 0x00e0; // 860 samples per second
const ADS1015_REG_CONFIG_CMODE_MASK = 0x0010;
const ADS1015_REG_CONFIG_CMODE_TRAD = 0x0000; // Traditional comparator with hysteresis (default)
const ADS1015_REG_CONFIG_CMODE_WINDOW = 0x0010; // Window comparator
const ADS1015_REG_CONFIG_CPOL_MASK = 0x0008;
const ADS1015_REG_CONFIG_CPOL_ACTVLOW = 0x0000; // ALERT/RDY pin is low when active (default)
const ADS1015_REG_CONFIG_CPOL_ACTVHI = 0x0008; // ALERT/RDY pin is high when active
const ADS1015_REG_CONFIG_CLAT_MASK = 0x0004; // Determines if ALERT/RDY pin latches once asserted
const ADS1015_REG_CONFIG_CLAT_NONLAT = 0x0000; // Non-latching comparator (default)
const ADS1015_REG_CONFIG_CLAT_LATCH = 0x0004; // Latching comparator
const ADS1015_REG_CONFIG_CQUE_MASK = 0x0003;
const ADS1015_REG_CONFIG_CQUE_1CONV = 0x0000; // Assert ALERT/RDY after one conversions
const ADS1015_REG_CONFIG_CQUE_2CONV = 0x0001; // Assert ALERT/RDY after two conversions
const ADS1015_REG_CONFIG_CQUE_4CONV = 0x0002; // Assert ALERT/RDY after four conversions
const ADS1015_REG_CONFIG_CQUE_NONE = 0x0003; // Disable the comparator and put ALERT/RDY in high state (default)

// This is a javascript port of python, so use objects instead of dictionaries here
// These simplify and clean the code (avoid the abuse of if/elif/else clauses)
const spsADS1115 = {
  8: ADS1115_REG_CONFIG_DR_8SPS,
  16: ADS1115_REG_CONFIG_DR_16SPS,
  32: ADS1115_REG_CONFIG_DR_32SPS,
  64: ADS1115_REG_CONFIG_DR_64SPS,
  128: ADS1115_REG_CONFIG_DR_128SPS,
  250: ADS1115_REG_CONFIG_DR_250SPS,
  475: ADS1115_REG_CONFIG_DR_475SPS,
  860: ADS1115_REG_CONFIG_DR_860SPS
};

const spsADS1015 = {
  128: ADS1015_REG_CONFIG_DR_128SPS,
  250: ADS1015_REG_CONFIG_DR_250SPS,
  490: ADS1015_REG_CONFIG_DR_490SPS,
  920: ADS1015_REG_CONFIG_DR_920SPS,
  1600: ADS1015_REG_CONFIG_DR_1600SPS,
  2400: ADS1015_REG_CONFIG_DR_2400SPS,
  3300: ADS1015_REG_CONFIG_DR_3300SPS
};

// Dictionary with the programable gains

const pgaADS1x15 = {
  6144: ADS1015_REG_CONFIG_PGA_6_144V,
  4096: ADS1015_REG_CONFIG_PGA_4_096V,
  2048: ADS1015_REG_CONFIG_PGA_2_048V,
  1024: ADS1015_REG_CONFIG_PGA_1_024V,
  512: ADS1015_REG_CONFIG_PGA_0_512V,
  256: ADS1015_REG_CONFIG_PGA_0_256V
};

module.exports = class ads1x15 {
  constructor(ic = IC_ADS1015, address = 0x48, i2cDevice = 1) {
    if (ic !== IC_ADS1015 && ic !== IC_ADS1115) {
      throw new Error("Error: not a supported device");
    }
    this.ic = ic; // 0 for ads1015, 1 for ads1115;
    this.address = address; //defaults to 0x48 for addr pin tied to ground
    this.pga = 6144; //set this to a sane default...
    this.wire = i2c.openSync(1);
    this.busy = false;
  }

  read(command, numBytes, callback) {
    const buffer = Buffer.alloc(numBytes);
    this.wire.readI2cBlock(
      this.address,
      command,
      numBytes,
      buffer,
      (err, _bytesRead, responseBuffer) => callback(err, responseBuffer)
    );
  }

  write(command, buffer, callback) {
    buffer = Buffer.from(buffer);

    this.wire.writeI2cBlock(
      this.address,
      command,
      buffer.length,
      buffer,
      callback
    );
  }

  // Gets a single-ended ADC reading from the specified channel in mV. \
  // The sample rate for this mode (single-shot) can be used to lower the noise \
  // (low sps) or to lower the power consumption (high sps) by duty cycling, \
  // see datasheet page 14 for more info. \
  // The pga must be given in mV, see page 13 for the supported values.
  readADCSingleEnded(channel = 0, pga = 6144, sps = 250, callback) {
    if (!this.busy) {
      this.busy = true;

      if (channel > 3 || channel < 0) {
        this.busy = false;
        return callback("Error: Channel must be between 0 and 3");
      }

      // Disable comparator, Non-latching, Alert/Rdy active low
      // traditional comparator, single-shot mode
      let config =
        ADS1015_REG_CONFIG_CQUE_NONE |
        ADS1015_REG_CONFIG_CLAT_NONLAT |
        ADS1015_REG_CONFIG_CPOL_ACTVLOW |
        ADS1015_REG_CONFIG_CMODE_TRAD |
        ADS1015_REG_CONFIG_MODE_SINGLE;

      // Set sample per seconds, defaults to 250sps
      // If sps is in the dictionary (defined in init) it returns the value of the constant
      // othewise it returns the value for 250sps. This saves a lot of if/elif/else code!

      if (this.ic === IC_ADS1015) {
        if (spsADS1015[sps]) {
          config |= spsADS1015[sps];
        } else {
          return callback("ADS1x15: Invalid sps specified");
        }
      } else {
        if (!spsADS1115[sps]) {
          this.busy = false;
          return callback("ADS1x15: Invalid sps specified");
        } else {
          config |= spsADS1115[sps];
        }
      }
      // Set PGA/voltage range, defaults to +-6.144V
      if (!pgaADS1x15[pga]) {
        this.busy = false;
        return callback("ADS1x15: Invalid pga specified");
      } else {
        config |= pgaADS1x15[pga];
      }
      this.pga = pga;

      // Set the channel to be converted
      if (channel == 3) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_3;
      } else if (channel == 2) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_2;
      } else if (channel == 1) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_1;
      } else {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_0;
      }

      // Set 'start single-conversion' bit
      config |= ADS1015_REG_CONFIG_OS_SINGLE;

      // Write config register to the ADC
      this.write(
        ADS1015_REG_POINTER_CONFIG,
        [(config >> 8) & 0xff, config & 0xff],
        err => {
          if (err) {
            this.busy = false;
            return callback(err);
          }

          // Wait for the ADC conversion to complete
          // The minimum delay depends on the sps: delay >= 1s/sps
          // We add 1ms to be sure
          const delay = 1000 / sps + 1;
          setTimeout(() => {
            // Read the conversion results
            this.read(ADS1015_REG_POINTER_CONVERT, 2, (err, res) => {
              if (err) {
                this.busy = false;
                return callback(err);
              }
              let data = -0.1;
              if (this.ic == IC_ADS1015) {
                // Shift right 4 bits for the 12-bit ADS1015 and convert to mV
                data =
                  ((((res[0] << 8) | (res[1] & 0xff)) >> 4) * this.pga) /
                  2048.0;
                this.busy = false;
                return callback(null, data);
              } else {
                // Return a mV value for the ADS1115
                // (Take signed values into account as well)
                const val = (res[0] << 8) | res[1];
                if (val > 0x7fff) {
                  data = ((val - 0xffff) * pga) / 32768.0;
                } else {
                  data = (((res[0] << 8) | res[1]) * pga) / 32768.0;
                }
                this.busy = false;
                return callback(null, data);
              }
            });
          }, delay);
        }
      );
    } else {
      callback("ADC is busy...");
    }
  }

  // Gets a differential ADC reading from channels chP and chN in mV. \
  // The sample rate for this mode (single-shot) can be used to lower the noise \
  // (low sps) or to lower the power consumption (high sps) by duty cycling, \
  // see data sheet page 14 for more info. \
  // The pga must be given in mV, see page 13 for the supported values.

  readADCDifferential(chP, chN, pga, sps, callback) {
    if (!this.busy) {
      this.busy = true;
      //set defaults if not provided
      if (!chP) chP = 0;
      if (!chN) chN = 1;
      if (!pga) pga = 6144;
      if (!sps) sps = 250;

      // Disable comparator, Non-latching, Alert/Rdy active low
      // traditional comparator, single-shot mode
      config =
        ADS1015_REG_CONFIG_CQUE_NONE |
        ADS1015_REG_CONFIG_CLAT_NONLAT |
        ADS1015_REG_CONFIG_CPOL_ACTVLOW |
        ADS1015_REG_CONFIG_CMODE_TRAD |
        ADS1015_REG_CONFIG_MODE_SINGLE;

      // Set channels
      if ((chP == 0) & (chN == 1)) {
        config |= ADS1015_REG_CONFIG_MUX_DIFF_0_1;
      } else if ((chP == 0) & (chN == 3)) {
        config |= ADS1015_REG_CONFIG_MUX_DIFF_0_3;
      } else if ((chP == 2) & (chN == 3)) {
        config |= ADS1015_REG_CONFIG_MUX_DIFF_2_3;
      } else if ((chP == 1) & (chN == 3)) {
        config |= ADS1015_REG_CONFIG_MUX_DIFF_1_3;
      } else {
        this.busy = false;
        callback("ADS1x15: Invalid channels specified");
      }

      // Set sample per seconds, defaults to 250sps
      // If sps is in the dictionary (defined in init()) it returns the value of the constant
      // othewise it returns the value for 250sps. This saves a lot of if/elif/else code!
      if (this.ic == IC_ADS1015) {
        config |= spsADS1015[sps];
      } else {
        if (!spsADS1115[sps]) {
          this.busy = false;
          callback("ADS1x15: Invalid pga specified");
        } else {
          config |= spsADS1115[sps];
        }
      }
      // Set PGA/voltage range, defaults to +-6.144V
      if (!pgaADS1x15[pga]) {
        this.busy = false;
        callback("ADS1x15: Invalid pga specified");
      } else {
        config |= pgaADS1x15[pga];
        this.pga = pga;
      }
      // Set 'start single-conversion' bit
      config |= ADS1015_REG_CONFIG_OS_SINGLE;
      // Write config register to the ADC
      this.write(
        ADS1015_REG_POINTER_CONFIG,
        [(config >> 8) & 0xff, config & 0xff],
        err => {
          if (err) {
            this.busy = false;
            callback(
              "We've got an Error, Lance Constable Carrot!: " + err.toString()
            );
          }
        }
      );
      // Wait for the ADC conversion to complete
      // The minimum delay depends on the sps: delay >= 1s/sps
      // We add 1ms to be sure

      delay = 1000 / sps + 1;

      setTimeout(() => {
        this.read(ADS1015_REG_POINTER_CONVERT, 2, (err, res) => {
          if (this.ic == IC_ADS1015) {
            // Shift right 4 bits for the 12-bit ADS1015 and convert to mV
            var data =
              ((((res[0] << 8) | (res[1] & 0xff)) >> 4) * pga) / 2048.0;
            this.busy = false;
            callback(null, data);
          } else {
            // Return a mV value for the ADS1115
            // (Take signed values into account as well)
            var data = -1;
            var val = (res[0] << 8) | res[1];
            if (val > 0x7fff) {
              data = ((val - 0xffff) * pga) / 32768.0;
            } else {
              data = (((res[0] << 8) | res[1]) * pga) / 32768.0;
            }
            this.busy = false;
            callback(null, data);
          }
        });
      }, delay);
    } else {
      callback("ADC is busy...");
    }
  }

  // Gets a differential ADC reading from channels 0 and 1 in mV
  // The sample rate for this mode (single-shot) can be used to lower the noise
  // (low sps) or to lower the power consumption (high sps) by duty cycling,
  // see data sheet page 14 for more info.
  // The pga must be given in mV, see page 13 for the supported values.

  readADCDifferential01(pga, sps, callback) {
    if (!pga) pga = 6144;
    if (!sps) sps = 250;

    return this.readADCDifferential(0, 1, pga, sps, callback);
  }

  // Gets a differential ADC reading from channels 0 and 3 in mV
  // The sample rate for this mode (single-shot) can be used to lower the noise
  // (low sps) or to lower the power consumption (high sps) by duty cycling,
  // see data sheet page 14 for more info.
  // The pga must be given in mV, see page 13 for the supported values.

  readADCDifferential03(pga, sps, callback) {
    if (!pga) pga = 6144;
    if (!sps) sps = 250;
    return this.readADCDifferential(0, 3, pga, sps, callback);
  }

  // Gets a differential ADC reading from channels 1 and 3 in mV
  // The sample rate for this mode (single-shot) can be used to lower the noise
  // (low sps) or to lower the power consumption (high sps) by duty cycling,
  // see data sheet page 14 for more info.
  // The pga must be given in mV, see page 13 for the supported values.

  readADCDifferential13(pga, sps, callback) {
    if (!pga) pga = 6144;
    if (!sps) sps = 250;

    return this.readADCDifferential(1, 3, pga, sps, callback);
  }

  // Gets a differential ADC reading from channels 2 and 3 in mV
  // The sample rate for this mode (single-shot) can be used to lower the noise
  // (low sps) or to lower the power consumption (high sps) by duty cycling,
  // see data sheet page 14 for more info.
  // The pga must be given in mV, see page 13 for the supported values.

  readADCDifferential23(pga, sps, callback) {
    if (!pga) pga = 6144;
    if (!sps) sps = 250;

    return this.readADCDifferential(2, 3, pga, sps, callback);
  }

  // Starts the continuous conversion mode and returns the first ADC reading
  // in mV from the specified channel.
  // The sps controls the sample rate.
  // The pga must be given in mV, see datasheet page 13 for the supported values.
  // Use getLastConversionResults() to read the next values and
  // stopContinuousConversion() to stop converting.

  startContinuousConversion(channel, pga, sps, callback) {
    if (!this.busy) {
      this.busy = true;
      if (!channel) channel = 0;
      if (!pga) pga = 6144;
      if (!sps) sps = 250;

      // Default to channel 0 with invalid channel, or return -1?
      if (channel > 3) {
        this.busy = false;
        callback("ADS1x15: Invalid channel specified, Lance Corporal Carrot!");
      }

      // Disable comparator, Non-latching, Alert/Rdy active low
      // traditional comparator, continuous mode
      // The last flag is the only change we need, page 11 datasheet

      config =
        ADS1015_REG_CONFIG_CQUE_NONE |
        ADS1015_REG_CONFIG_CLAT_NONLAT |
        ADS1015_REG_CONFIG_CPOL_ACTVLOW |
        ADS1015_REG_CONFIG_CMODE_TRAD |
        ADS1015_REG_CONFIG_MODE_CONTIN;

      // Set sample per seconds, defaults to 250sps
      // If sps is in the dictionary (defined in init()) it returns the value of the constant
      // othewise it returns the value for 250sps. This saves a lot of if/elif/else code!
      if (this.ic == IC_ADS1015) {
        config |= spsADS1015[sps];
      } else {
        if (!spsADS1115[sps]) {
          this.busy = false;
          callback("ADS1x15: Invalid sps specified");
        } else {
          config |= spsADS1115[sps];
        }
      }
      // Set PGA/voltage range, defaults to +-6.144V
      if (!pgaADS1x15[pga]) {
        this.busy = false;
        callback("ADS1x15: Invalid pga specified");
      } else {
        config |= pgaADS1x15[pga];
      }
      this.pga = pga;

      // Set the channel to be converted
      if (channel == 3) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_3;
      } else if (channel == 2) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_2;
      } else if (channel == 1) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_1;
      } else {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_0;
      }
      // Set 'start single-conversion' bit to begin conversions
      // No need to change this for continuous mode!
      config |= ADS1015_REG_CONFIG_OS_SINGLE;

      // Write config register to the ADC
      // Once we write the ADC will convert continously
      // we can read the next values using getLastConversionResult

      this.write(
        ADS1015_REG_POINTER_CONFIG,
        [(config >> 8) & 0xff, config & 0xff],
        err => {
          if (err) {
            this.busy = false;
            callback(
              "We've got an Error, Lance Constable Carrot!: " + err.toString()
            );
          }
        }
      );
      // Wait for the ADC conversion to complete
      // The minimum delay depends on the sps: delay >= 1s/sps
      // We add 1ms to be sure

      delay = 1000 / sps + 1;
      setTimeout(() => {
        this.read(ADS1015_REG_POINTER_CONVERT, 2, (err, res) => {
          if (this.ic == IC_ADS1015) {
            // Shift right 4 bits for the 12-bit ADS1015 and convert to mV
            var data =
              ((((res[0] << 8) | (res[1] & 0xff)) >> 4) * pga) / 2048.0;
            callback(null, data);
          } else {
            // Return a mV value for the ADS1115
            // (Take signed values into account as well)
            var data = -1;
            var val = (res[0] << 8) | res[1];
            if (val > 0x7fff) {
              data = ((val - 0xffff) * pga) / 32768.0;
            } else {
              data = (((res[0] << 8) | res[1]) * pga) / 32768.0;
            }
            callback(null, data);
          }
        });
      }, delay);
    } else {
      callback("ADC is busy...");
    }
  }

  // Stops the ADC's conversions when in continuous mode \
  // and resets the configuration to its default value."

  stopContinuousConversion(callback) {
    // Write the default config register to the ADC
    // Once we write, the ADC will do a single conversion and
    //  enter power-off mode.
    config = 0x8583; // Page 18 datasheet.
    this.write(
      ADS1015_REG_POINTER_CONFIG,
      [(config >> 8) & 0xff, config & 0xff],
      err => {
        this.busy = false;
        if (err) {
          callback(err);
        } else return true;
      }
    );
  }

  // Returns the last ADC conversion result in mV

  getLastConversionResults(callback) {
    // Read the conversion results
    this.read(ADS1015_REG_POINTER_CONVERT, 2, (err, res) => {
      if (this.ic == IC_ADS1015) {
        // Shift right 4 bits for the 12-bit ADS1015 and convert to mV
        var data =
          ((((res[0] << 8) | (res[1] & 0xff)) >> 4) * this.pga) / 2048.0;
        callback(null, data);
      } else {
        // Return a mV value for the ADS1115
        // (Take signed values into account as well)
        var data = -1;
        var val = (res[0] << 8) | res[1];
        if (val > 0x7fff) {
          data = ((val - 0xffff) * this.pga) / 32768.0;
        } else {
          data = (((res[0] << 8) | res[1]) * this.pga) / 32768.0;
        }
      }
    });
  }

  // Starts the comparator mode on the specified channel, see datasheet pg. 15.
  // In traditional mode it alerts (ALERT pin will go low) when voltage exceeds
  // thresholdHigh until it falls below thresholdLow (both given in mV).
  // In window mode (traditionalMode=False) it alerts when voltage doesn't lie
  // between both thresholds.
  // In latching mode the alert will continue until the conversion value is read.
  // numReadings controls how many readings are necessary to trigger an alert: 1, 2 or 4.
  // Use getLastConversionResults() to read the current value (which may differ
  // from the one that triggered the alert) and clear the alert pin in latching mode.
  // This  starts the continuous conversion mode. The sps controls
  // the sample rate and the pga the gain, see datasheet page 13.

  startSingleEndedComparator(
    channel,
    thresholdHigh,
    thresholdLow,
    pga = 6144,
    sps = 250,
    activeLow = true,
    traditionalMode = true,
    latching = false,
    numReadings = 1,
    callback
  ) {
    if (!this.busy) {
      this.busy = true;

      // With invalid channel return -1
      if (channel > 3) {
        this.busy = false;
        callback("ADS1x15: Invalid channel specified");
      }

      // Continuous mode
      config = ADS1015_REG_CONFIG_MODE_CONTIN;
      if (activeLow == false) {
        config |= ADS1015_REG_CONFIG_CPOL_ACTVHI;
      } else {
        config |= ADS1015_REG_CONFIG_CPOL_ACTVLOW;
      }
      if (traditionalMode == false) {
        config |= ADS1015_REG_CONFIG_CMODE_WINDOW;
      } else {
        config |= ADS1015_REG_CONFIG_CMODE_TRAD;
      }
      if (latching == true) {
        config |= ADS1015_REG_CONFIG_CLAT_LATCH;
      } else {
        config |= ADS1015_REG_CONFIG_CLAT_NONLAT;
      }
      if (numReadings == 4) {
        config |= ADS1015_REG_CONFIG_CQUE_4CONV;
      } else if (numReadings == 2) {
        config |= ADS1015_REG_CONFIG_CQUE_2CONV;
      } else {
        config |= ADS1015_REG_CONFIG_CQUE_1CONV;
      }
      // Set sample per seconds, defaults to 250sps
      // If sps is in the dictionary (defined in init()) it returns the value of the constant
      // othewise it returns the value for 250sps. This saves a lot of if/elif/else code!
      if (this.ic == IC_ADS1015) {
        if (!spsADS1015[sps]) {
          this.busy = false;
          callback("ADS1x15: Invalid sps specified");
        }
        config |= spsADS1015[sps];
      } else {
        if (!spsADS1115[sps]) {
          this.busy = false;
          callback("ADS1x15: Invalid sps specified");
        }
        config |= spsADS1115[sps];
      }
      // Set PGA/voltage range, defaults to +-6.144V
      if (!pgaADS1x15[pga]) {
        this.busy = false;
        callback("ADS1x15: Invalid pga specified");
      }
      config |= pgaADS1x15[pga];
      this.pga = pga;

      // Set the channel to be converted
      if (channel == 3) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_3;
      } else if (channel == 2) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_2;
      } else if (channel == 1) {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_1;
      } else {
        config |= ADS1015_REG_CONFIG_MUX_SINGLE_0;
      }

      // Set 'start single-conversion' bit to begin conversions
      config |= DS1015_REG_CONFIG_OS_SINGLE;

      // Write threshold high and low registers to the ADC
      // V_digital = (2^(n-1)-1)/pga*V_analog
      var thresholdHighWord = 0;

      if (this.ic == IC_ADS1015) {
        thresholdHighWORD = int(thresholdHigh * (2048.0 / pga));
      } else {
        thresholdHighWORD = int(thresholdHigh * (32767.0 / pga));
      }

      this.write(
        ADS1015_REG_POINTER_HITHRESH,
        [(thresholdHighWORD >> 8) & 0xff, thresholdHighWORD & 0xff],
        err => {
          if (err) {
            this.busy = false;
            callback(err);
          }
        }
      );
      var thresholdLowWORD = 0;

      if (this.ic == IC_ADS1015) {
        thresholdLowWORD = int(thresholdLow * (2048.0 / pga));
      } else {
        thresholdLowWORD = int(thresholdLow * (32767.0 / pga));
      }

      this.write(
        ADS1015_REG_POINTER_LOWTHRESH,
        [(thresholdLowWORD >> 8) & 0xff, thresholdLowWORD & 0xff],
        err => {
          if (err) {
            this.busy = false;
            callback(err);
          }
        }
      );

      // Write config register to the ADC
      // Once we write the ADC will convert continously and alert when things happen,
      // we can read the converted values using getLastConversionResult
      this.write(
        ADS1015_REG_POINTER_CONFIG,
        [(config >> 8) & 0xff, config & 0xff],
        err => {
          if (err) {
            this.busy = false;
            callback(err);
          }
        }
      );
    } else {
      callback("ADC is busy...");
    }
  }

  // Starts the comparator mode on the specified channel, see datasheet pg. 15. \
  // In traditional mode it alerts (ALERT pin will go low) when voltage exceeds \
  // thresholdHigh until it falls below thresholdLow (both given in mV). \
  // In window mode (traditionalMode=False) it alerts when voltage doesn't lie\
  // between both thresholds.\
  // In latching mode the alert will continue until the conversion value is read. \
  // numReadings controls how many readings are necessary to trigger an alert: 1, 2 or 4.\
  // Use getLastConversionResults() to read the current value (which may differ \
  // from the one that triggered the alert) and clear the alert pin in latching mode. \
  // This  starts the continuous conversion mode. The sps controls \
  // the sample rate and the pga the gain, see datasheet page 13. "

  startDifferentialComparator(
    chP,
    chN,
    thresholdHigh,
    thresholdLow,
    pga = 6144,
    sps = 250,
    activeLow = true,
    traditionalMode = true,
    latching = false,
    numReadings = 1,
    callback
  ) {
    if (!this.busy) {
      this.busy = true;

      // Continuous mode
      config = ADS1015_REG_CONFIG_MODE_CONTIN;
      if (activeLow == False) {
        config |= ADS1015_REG_CONFIG_CPOL_ACTVHI;
      } else {
        config |= ADS1015_REG_CONFIG_CPOL_ACTVLOW;
      }
      if (!traditionalMode) {
        config |= ADS1015_REG_CONFIG_CMODE_WINDOW;
      } else {
        config |= ADS1015_REG_CONFIG_CMODE_TRAD;
      }
      if (latching) {
        config |= ADS1015_REG_CONFIG_CLAT_LATCH;
      } else {
        config |= ADS1015_REG_CONFIG_CLAT_NONLAT;
      }
      if (numReadings == 4) {
        config |= ADS1015_REG_CONFIG_CQUE_4CONV;
      } else if (numReadings == 2) {
        config |= ADS1015_REG_CONFIG_CQUE_2CONV;
      } else {
        config |= ADS1015_REG_CONFIG_CQUE_1CONV;
      }

      // Set sample per seconds, defaults to 250sps
      // If sps is in the dictionary (defined in init()) it returns the value of the constant
      // othewise it returns the value for 250sps. This saves a lot of if/elif/else code!
      if (this.ic == IC_ADS1015) {
        if (!spsADS1015[sps]) {
          this.busy = false;
          callback("ADS1x15: Invalid sps specified");
        }
        config |= spsADS1015[sps];
      } else {
        if (!spsADS1115[sps]) {
          this.busy = false;
          callback("ADS1x15: Invalid sps specified");
        }
        config |= spsADS1115[sps];
      }

      // Set PGA/voltage range, defaults to +-6.144V
      if (!pgaADS1x15[pga]) {
        this.busy = false;
        callback("ADS1x15: Invalid pga specified");
      }
      config |= pgaADS1x15[pga];
      this.pga = pga;

      // Set channels
      if ((chP == 0) & (chN == 1)) {
        config |= ADS1015_REG_CONFIG_MUX_DIFF_0_1;
      } else if ((chP == 0) & (chN == 3)) {
        config |= ADS1015_REG_CONFIG_MUX_DIFF_0_3;
      } else if ((chP == 2) & (chN == 3)) {
        config |= ADS1015_REG_CONFIG_MUX_DIFF_2_3;
      } else if ((chP == 1) & (chN == 3)) {
        config |= ADS1015_REG_CONFIG_MUX_DIFF_1_3;
      } else {
        this.busy = false;
        callback("ADS1x15: Invalid channels specified");
      }
      // Set 'start single-conversion' bit to begin conversions
      config |= ADS1015_REG_CONFIG_OS_SINGLE;

      // Write threshold high and low registers to the ADC
      // V_digital = (2^(n-1)-1)/pga*V_analog;

      var thresholdHighWORD = 0;
      if (this.ic == IC_ADS1015) {
        thresholdHighWORD = int(thresholdHigh * (2048.0 / pga));
      } else {
        thresholdHighWORD = int(thresholdHigh * (32767.0 / pga));
      }

      this.write(
        ADS1015_REG_POINTER_HITHRESH,
        [(thresholdHighWORD >> 8) & 0xff, thresholdHighWORD & 0xff],
        err => {
          callback(err);
        }
      );

      var thresholdLowWORD = 0;
      if (this.ic == IC_ADS1015) {
        thresholdLowWORD = int(thresholdLow * (2048.0 / pga));
      } else {
        thresholdLowWORD = int(thresholdLow * (32767.0 / pga));
      }

      this.write(
        ADS1015_REG_POINTER_LOWTHRESH,
        [(thresholdLowWORD >> 8) & 0xff, thresholdLowWORD & 0xff],
        err => {
          if (err) {
            this.busy = false;
            callback(err);
          }
        }
      );

      // Write config register to the ADC
      // Once we write the ADC will convert continously and alert when things happen,
      // we can read the converted values using getLastConversionResult
      this.write(
        ADS1015_REG_POINTER_CONFIG,
        [(config >> 8) & 0xff, config & 0xff],
        err => {
          if (err) {
            this.busy = false;
            callback(err);
          }
        }
      );
    } else {
      callback("ADC is busy...");
    }
  }
};