Temperature Measurement Using STS21 and Arduino Nano

Introduction

STS21 Digital Temperature Sensor offers superior performance and a space saving footprint. It provides calibrated, linearized signals in digital, I2C format. Fabrication of this sensor is based on CMOSens technology, which attributes to the superior performance and reliability of STS21. The resolution of STS21 can be changed by command, low battery can be detected and a checksum helps to improve communication reliability.

In this tutorial the interfacing of the STS21 sensor module with Arduino Nano has been illustrated. To read the temperature values, we have used Arduino with an I2C adapter. This I2C adapter makes the connection to the sensor module easy and more reliable.

Step 1: Hardware Required

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

1. STS21

2. Arduino Nano

3. I2C Cable

4. I2C shield for Arduino Nano

Step 2: Hardware Hookup

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

• The STS21 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 3: Code for temperature measurement

Lets start with the Arduino code now.

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

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

#include 
// STS21 I2C address is 0x4A(74)
#define addr 0x4A
void setup()
{  
// Initialise I2C communication as MASTER  
Wire.begin();  
// Start serial communication, set baud rate = 9600  
Serial.begin(9600);  
delay(300);
}
void loop()
{  
unsigned int data[2];
// Start I2C Transmission  
Wire.beginTransmission(addr);  
// Select no hold master  
Wire.write(0xF3);  
// End I2C Transmission  
Wire.endTransmission();  
delay(300);
// Request 2 bytes of data  
Wire.requestFrom(addr, 2);
// Read 2 bytes of data  
if (Wire.available() == 2)  
{    
data[0] = Wire.read();    
data[1] = Wire.read();  
}
// Convert the data  
int rawtmp = data[0] * 256 + data[1];  
int value = rawtmp & 0xFFFC;  
double cTemp = -46.85 + (175.72 * (value / 65536.0));  
double fTemp = cTemp * 1.8 + 32;
// Output data to serial monitor  
Serial.print("Temperature in Celsius:  ");  
Serial.print(cTemp);  
Serial.println(" C");  
Serial.print("Temperature in Fahrenheit:  ");  
Serial.print(fTemp);  
Serial.println(" F");  
delay(300);
}

In wire library Wire.write() and Wire.read() is used to write the commands and read the sensor output. Serial.print() and Serial.println() is used to display the output of the sensor on the serial monitor of the Arduino IDE.

The output of the sensor is shown in the picture above.

Step 4: Applications

STS21 Digital Temperature Sensor can be employed in systems which require high accuracy temperature monitoring. It can be incorporated in various computer equipment, medical equipment and industrial control systems with the requisite of temperature measurement with proficient accuracy.