Temperature and Humidity Monitoring Using SHT25 and Particle

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 with Particle Photon.

Step 1: SHT25 Overview

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, linearized 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.

Step 2: What you need

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

1. SHT25 humidity and temperature sensor

2. Particle Photon

3. I2C Cable

4. I2C Shield for Particle Photon

Step 3: Hardware Hookup

The hardware hookup section basically explains the wiring connections required between the sensor and the Particle Photon. 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.

Step 4: Temperature and Humidity Monitoring Code

Lets start with the Particle code now.

While using the sensor module with the Arduino, we include application.h and spark_wiring_i2c.h library. "application.h " and spark_wiring_i2c.h library contains the functions which facilitate the I2C communication between the sensor and the Particle.

The entire Particle code is given below for the convenience of the user:

#include 
#include 
// SHT25 I2C address is 0x40(64)
#define Addr 0x40
float humidity = 0.0, cTemp = 0.0, fTemp = 0.0;
void setup() 
{    
// Set variable    
Particle.variable("i2cdevice", "SHT25");    
Particle.variable("humidity", humidity);    
Particle.variable("cTemp", cTemp);      
// Initialise I2C communication as MASTER     
Wire.begin();    
// Initialise serial communication, set baud rate = 9600    
Serial.begin(9600);    
delay(300);
}
void loop() 
{    
unsigned int data[2];    
// Start I2C communication    
Wire.beginTransmission(Addr);    
// Send humidity measurement command, NO HOLD master    
Wire.write(0xF5);    
// Stop I2C transmission    
Wire.endTransmission();    
delay(500);
// Request 2 bytes of data    
Wire.requestFrom(Addr, 2);
// Read 2 bytes of data    
// humidity msb, humidity lsb    
if(Wire.available() == 2)    
{        
data[0] = Wire.read();        
data[1] = Wire.read();                
// Convert the data        
humidity = ((((data[0] * 256.0) + data[1]) * 125.0) / 65536.0) - 6;                 
// Output data to dashboard        
Particle.publish("Relative Humidity    :  ",  String(humidity));    
}
// Start I2C transmission    
Wire.beginTransmission(Addr);    
// Send temperature measurement command, NO HOLD master               
Wire.write(0xF3);    
// Stop I2C transmission    
Wire.endTransmission();    
delay(500);        
// Request 2 bytes of data    
Wire.requestFrom(Addr,2);
// Read 2 bytes of data    
// temp msb, temp lsb    
if(Wire.available() == 2)    
{        
data[0] = Wire.read();        
data[1] = Wire.read();                
// Convert the data        
cTemp = ((((data[0] * 256.0) + data[1]) * 175.72) / 65536.0) - 46.85;        
fTemp = (cTemp * 1.8) + 32;                
// Output data to dashboard        
Particle.publish("Temperature in Celsius:  ",  String(cTemp));        
Particle.publish("Temperature in Fahrenheit:  ", String(fTemp));    
}   
delay(300);
}

Particle.variable() function creates the variables to store the output of the sensor and Particle.publish() function displays the output on the dashboard of the site.

The sensor output is shown in the picture above for your reference.

Step 5: Applications

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