i2c-adt7420

Node.js driver for the acurate (±0.25°C) yet affordable ADT7420 digital temperature sensor. Should also work with the less accurate ADT7410.

This module was tested with Raspberry Pi 3B and 4B, wired to an EVAL-ADT7420-PMDZ breakout board. Please do note that the power LED on the EVAL-ADT7420-PMDZ board significantly influences the temperature reading! The LED or its series resistor should be desoldered if you need accurate temperature.

Supported features:

• 13 and 16 bit resolution
• Continuous and one sample per second modes
• Alternate I2C addresses

Installation

Available from npm: npm install i2c-adt7420

Requires Node.js 14 or higher.

Example: ADT7420 temperature server

const express = require('express');
const {ADT7420} = require('i2c-adt7420');

const config = {
  pollingInterval: 1000,
  httpPort: 7420,
  i2cBusNumber: 1
};

const app = express();
let adt7420 = null;
let lastUpdateTime = null;
let temperature = null;

app.get('/', (req, res) => {
  res.setHeader('Content-Type', 'application/json');
  res.send(JSON.stringify({
    temperature: {
      raw: temperature.raw,
      celsius: temperature.celsius,
      kelvin: temperature.kelvin
    },
    time_updated: lastUpdateTime
  }, null, 2));
})

ADT7420.open({
  i2cBusNumber: config.i2cBusNumber
})
  .then((instance) => {
    adt7420 = instance;
    return adt7420.configure({
      resolution: 16,
      lowPowerMode: (config.pollingInterval >= 1000)
    });
  })
  .then(() => {
    console.log('Configured ADT7420');
    return updateTemperature();
  })
  .then(() => {
    console.log(`Read temperature of ${temperature.celsius}C`);
    setInterval(updateTemperature, config.pollingInterval);
    app.listen(config.httpPort, () => {
      console.log(`Serving temperature data on port ${config.httpPort}`);
    });
  })
  .catch((err) => {
    console.error(err);
    process.exit(3);
  });

function updateTemperature() {
  return adt7420.readTemperature()
    .then((result) => {
      lastUpdateTime = new Date();
      temperature = result;
    })
    .catch((err) => {
      console.error(err);
      process.exit(3);
    });
}

API

Class ADT7420

ADT7420.open([options]) -> Promise

Factory method to asynchronously create an instance of the class.

Arguments:

• options object of options:
  • i2cBusNumber Optional integer specifying the system's I2C device number of the bus the chip is attached to. If you use a Raspberry Pi, this should typically be 1 for a Raspberry Pi 2+ and 0 for the original model. Make sure the operating system supports I2C and that it is enabled. Default: 0.
  • i2cAddress Optional, one of ADT7420.I2C_ADDRESS_0x48 (default), ADT7420.I2C_ADDRESS_0x49, ADT7420.I2C_ADDRESS_0x4A, ADT7420.I2C_ADDRESS_0x4B. This only needs to be specified if you have changed the default address of the chip by physically connecting its address configuration pins.

Returns: promise resolving to an ADT7420 class instance when succesful.

ADT7420#configure([options]) -> Promise

Changes the chip's configuration register. Configuring is recommended but not mandatory.

Arguments:

• options object of options:
  • resolution Optional integer specifying the sample resolution in bits (either 13 or 16). The chip's reset value is 13 bits.
  • lowPowerMode Optional boolean, false for continuous sample mode, true for one sample per second mode. The chip's reset value is false (continuous mode). See datasheet for details.

Returns: promise resolving to undefined when succesful.

ADT7420#readTemperature() -> Promise

Reads the chip's temperature register.

Returns: promise resolving to an ADT7420Temperature instance when succesful.

Class ADT7420Temperature

ADT7420Temperature#raw : Number

Raw temperature reading as a 16-bit two's complement integer.

ADT7420Temperature#celsius : Number

Temperature reading converted to degrees Celsius.

ADT7420Temperature#kelvin : Number

Temperature reading converted to Kelvin.