Raspberry Pi and Si7021 sensor java example

In this example we will connect an SI7021 digital temperature sensor to a Raspberry Pi and use Java to display the temperature readings, there are other languages such as C and python which work as well but I wanted to try something a little different

Here is a recap of the sensor

The Silicon Labs Si7006/13/20/21/34 devices are our latest generation of I2C relative humidity and temperature sensors. All members of this device family combine fully factory-calibrated humidity and temperature sensor elements with an analog to digital converter, signal processing, and an I2C host interface.  The Si7013/20/21/34 devices are designed for high-accuracy applications, while the Si7006 is targeted toward lower-accuracy applications traditionally using discrete RH/T sensors.

The innovative CMOS design of these devices offers the lowest power consumption in the industry for a relative humidity and temperature sensor. Patented use of industry-standard low-K polymer dielectrics provides excellent accuracy and long-term stability, along with low drift and low hysteresis.


You can read more – https://www.silabs.com/products/sensors/humidity/si7006-13-20-21-34


Parts List

Label Part Type
Part1 Adafruit Si7021 Temp Humidity
Raspberry Pi1 Raspberry Pi 2



pi and si7021
pi and si7021


This time we explore the world of Java on the Raspberry Pi

First you need to install PI4j – http://pi4j.com/install.html . I’ll sum it up as its easy to install from a terminal

The simplest method to install Pi4J on your RaspberryPi is to execute the following command directly on your RaspberryPi.
curl -s get.pi4j.com | sudo bash

Now for the java code – this is courtesy of a controleverything example

[codesyntax lang=”java”]

// Distributed with a free-will license.
// Use it any way you want, profit or free, provided it fits in the licenses of its associated works.
// SI7021
// This code is designed to work with the SI7021_I2CS I2C Mini Module available from ControlEverything.com.
// https://www.controleverything.com/content/Humidity?sku=SI7021_I2CS#tabs-0-product_tabset-2

import com.pi4j.io.i2c.I2CBus;
import com.pi4j.io.i2c.I2CDevice;
import com.pi4j.io.i2c.I2CFactory;
import java.io.IOException;

public class SI7021
	public static void main(String args[]) throws Exception
		// Create I2C bus
		I2CBus bus = I2CFactory.getInstance(I2CBus.BUS_1);
		// Get I2C device, SI7021 I2C address is 0x40(64)
		I2CDevice device = bus.getDevice(0x40);
		// Send humidity measurement command
		// Read 2 bytes of humidity data, msb first
		byte[] data = new byte[2];
		device.read(data, 0, 2);
		// Convert humidity data
		double humidity = (((((data[0] & 0xFF) * 256) + (data[1] & 0xFF)) * 125.0) / 65536.0) - 6;
		// Send temperature measurement command
		// Read 2 bytes of temperature data, msb first
		device.read(data, 0, 2);
		// Convert temperature data
		double cTemp = (((((data[0] & 0xFF) * 256) + (data[1] & 0xFF)) * 175.72) / 65536.0) - 46.85;
		double fTemp = (cTemp * 1.8 ) + 32;
		// Output data to screen
		System.out.printf("Relative Humidity : %.2f %% %n", humidity);
		System.out.printf("Temperature in Celsius : %.2f C%n", cTemp);
		System.out.printf("Temperature in Fahrenheit : %.2f F%n", fTemp);



Now you have to compile and run the program like this

$> sudo pi4j SI7021.java


You should see the following

si7021 output
si7021 output


Industrial High Precision Si7021 Humidity Sensor with I2C Interface for Arduino

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