Lesson 35: Using HTU21D Temperature Sensor with Arduino

Lesson 35: Using HTU21D Temperature Sensor with Arduino

This project guides you through using an Arduino to read temperature and humidity data from an HTU21D-F sensor. This sensor is inexpensive and widely available, making it perfect for a variety of projects. The sensor outputs data via I2C, a common digital communication protocol. Learning to use this sensor and I2C will open up many possibilities for your projects.

Practical Applications:

Building a smart home environmental monitor
Creating a weather station
Developing a climate-controlled enclosure for sensitive electronics
Monitoring temperature and humidity in a greenhouse or terrarium

Hardware/Components

You will need the following components:

Arduino board (e.g., Uno, Nano)
HTU21D-F temperature and humidity sensor (in video at 00:22)
Connecting wires
Breadboard (optional, but recommended)

Wiring Guide

The wiring is straightforward. Connect the sensor to the Arduino as follows (in video at 02:28):

Sensor VCC to Arduino 3.3V
Sensor GND to Arduino GND
Sensor SDA to Arduino A4
Sensor SCL to Arduino A5

Arduino wiring for HTU21DF light intesity sensor

Code Explanation

The provided code uses the Adafruit HTU21D-F library (in video at 03:03) to interact with the sensor. The key parts are:


// These are the lines that you can configure:
const int inPin =A0;//can change
const int iteration = 1000; //can change (see video at 00:22)
const float LM35_FACTOR =0.01;// do not change

inPin: Specifies the analog pin connected to the temperature sensor. You can change this to suit your wiring.

iteration: This variable controls the number of readings taken to average the temperature. Increasing it improves accuracy but slows down the readings (in video at 00:22).

The getHTU() function (in video at 08:46) allows you to retrieve the temperature in Celsius, Fahrenheit, or Kelvin, or the humidity, by passing a character ('C', 'F', 'K', or 'H') as an argument. The code then uses this function to display the data on the serial monitor.


float getTemperature(char type) {
  // ... (code to read temperature and humidity) ...
  if (type == 'F') {
    value = averageTemperature * 9 / 5 + 32; // Fahrenheit
  } else if (type == 'K') {
    value = averageTemperature + 273.15; // Kelvin
  } else {
    value = averageTemperature; // Celsius
  }
  return value;
}

Live Project/Demonstration

The video demonstrates the sensor's functionality (in video at 07:34). The serial monitor displays the temperature and humidity readings. The presenter also shows how the code can trigger actions based on temperature thresholds (in video at 06:45).