Introduction: Temperature Measurement Using STS21 and Particle Photon
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 particle photon has been illustrated. To read the temperature values, we have used photon 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:
3. I2C Cable
Step 2: 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 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 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:
// STS21 I2C address is 0x4A(74)
#define addr 0x4A
float cTemp = 0.0;
// Set variable
// Initialise I2C communication as MASTER
// Start serial communication, set baud rate = 9600
unsigned int data;
// Start I2C Transmission
// Select no hold master
// End I2C Transmission
// Request 2 bytes of data
// Read 2 bytes of data
if (Wire.available() == 2)
data = Wire.read();
data = Wire.read();
// Convert the data
int rawtmp = data * 256 + data;
int value = rawtmp & 0xFFFC;
cTemp = -46.85 + (175.72 * (value / 65536.0));
float fTemp = cTemp * 1.8 + 32;
// Output data to dashboard
Particle.publish("Temperature in Celsius : ", String(cTemp));
Particle.publish("Temperature in Fahrenheit: ", String(fTemp));
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 4: Applications:
STS21 Digital Temperature Sensor can be employed in systems which require high accuracy temperature monitoring. It can be incorporated in various computer equipments, medical equipments and industrial control systems with the requisite of temperature measurement with proficient accuracy.