Temperature and Humidity Monitoring Using SHT25 and Raspberry Pi

We have recently worked on various projects which required temperature and humidity monitoring and then we realized that these two parameters actually play a pivotal role in having an estimate of the working efficiency of a system. Both at the industrial level and personal systems an optimum temperature level is the requisite for the adequate performance of the system.

This is the reason, in this tutorial we are going to explain the working of the SHT25 humidity and temperature sensor using raspberry pi. In this particular tutorial its working is being demonstrated using a java code.

Hardware that you are going to need for this purpose are:

1. SHT25

2. Raspberry Pi

3. I2C Cable

4. I2C shield for raspberry pi

First of all lets start with the basic understanding of the sensor and the protocol on which it works.

SHT25 I2C Humidity and Temperature Sensor ±1.8%RH ±0.2°C I2C Mini Module. It is high-accuracy humidity and temperature sensor has become an industry standard in terms of form factor and intelligence, providing calibrated, linearised sensor signals in digital, I2C format. Integrated with a specialized analog and digital circuit this sensor is one of the most efficient device to measure the temperature and humidity.

The communication protocol on which the sensor works is I2C. I2C stands for the inter-integrated circuit. It is a communication protocol in which the communication takes place through SDA(serial data) and SCL(serial clock) lines. It allows connecting multiple devices at the same time. It is one of the simplest and most efficient communication protocol.

The materials that we need for accomplishing our goal includes the following hardware components:

1. SHT25 humidity and temperature sensor

2. Raspberry pi

3. I2C Cable

4. I2C Shield for Raspberry Pi

5. Ethernet Cable

The hardware hookup section basically explains the wiring connections required between the sensor and the raspberry pi. Ensuring correct connections is the basic necessity while working on any system for the desired output. So, the requisite connections are as follows:

• The SHT25 will work over I2C . Here is the example wiring diagram, demonstrating how to wire up each interface of the sensor.
• Out-of-the-box, the board is configured for an I2C interface, as such we recommend using this hookup if you’re otherwise agnostic. All you need is four wires!
• Only four connections are required Vcc, Gnd, SCL and SDA pins and these are connected with the help of I2C cable.

These connections are demonstrated in the pictures above.

The advantage of using raspberry pi is, that is provides you the flexibility of the programming language in which you want to program the board in order to interface the sensor with it. Harnessing this advantage of this board, we are demonstrating here its programming in the Java. The Java code for SHT25 can be downloaded from our github community that is Dcube Store.

As well as for the ease of the users, we are explaining the code here also:

As the first step of coding you need to download the pi4j library in case of java, because this library supports the functions used in the code. So, to download the library you can visit the following link:

http://pi4j.com/install.html

You can copy the working java code for this sensor from here also:

import com.pi4j.io.i2c.I2CBus;
import com.pi4j.io.i2c.I2CDevice;
import com.pi4j.io.i2c.I2CFactory;
import java.io.IOException;
public class SHT25
{
public static void main(String args[]) throws Exception
{

// Create I2C bus
I2CBus Bus = I2CFactory.getInstance(I2CBus.BUS_1);

// Get I2C device, SHT25 I2C address is 0x40(64)
I2CDevice device = Bus.getDevice(0x40);

// Send temprature measurement command, NO HOLD master
device.write((byte)0xF3);
Thread.sleep(500);

// Read 2 bytes of data
// temp msb, temp lsb
byte[] data = new byte[2];
device.read(data, 0, 2);

// Convert the data
double cTemp = (((((data[0] & 0xFF) * 256) + (data[1] & 0xFF)) * 175.72) / 65536.0) - 46.85;
double fTemp = (cTemp * 1.8) + 32;

// Send humidity measurement command, NO HOLD master
device.write((byte)0xF5);
Thread.sleep(500);

// Read 2 bytes of data
// humidity msb, humidity lsb
device.read(data, 0, 2);

// Convert the data
double humidity = (((((data[0] & 0xFF) * 256) + (data[1] & 0xFF)) * 125.0) / 65536.0) - 6;

// Output data to screen
System.out.printf("Relative Humidity : %.2f %% RH %n", humidity);
System.out.printf("Temperature in Celsius : %.2f C %n", cTemp);
System.out.printf("Temperature in Farhenheit : %.2f F %n", fTemp);
}
}

The output of the code is also shown in the picture above.

The library which facilitates i2c communication between the sensor and the board is pi4j, its various packages I2CBus, I2CDevice and I2CFactory help to establish the connection.

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

This part of the code makes the sensor operate for temperature measurement and humidity measurement by writing the respective commands using the write() function and then the data is read using the read() function.

<p>device.write((byte)0xF3);</p><p>Thread.sleep(500);</p><p>// Read 2 bytes of data</p><p>// temp msb, temp lsb</p><p>byte[] data = new byte[2];</p><p>device.read(data, 0, 2);</p><p>// Send humidity measurement command, NO HOLD master</p><p>device.write((byte)0xF5);</p><p>Thread.sleep(500);</p><p>// Read 2 bytes of data</p><p>// humidity msb, humidity lsb</p><p>device.read(data, 0, 2);</p>

SHT25 temperature and relative humidity sensor has various industrial applications like temperature monitoring, computer peripheral thermal protection. We have also employed this sensor into weather station applications as well as greenhouse monitoring system.