Particle Photon - HTS221 Relative Humidity and Temperature Sensor Tutorial

HTS221 is an ultra compact capacitive digital sensor for relative humidity and temperature. It includes a sensing element and a mixed signal application specific integrated circuit(ASIC) to provide the measurement information through digital serial interfaces. Integrated with so many features this is one of the most appropriate sensors for critical humidity and temperature measurements. Here is the demonstration with particle photon.

1. Particle Photon

2. HTS221

3. I²C Cable

4. I²C Shield for Particle Photon

Take an I2C shield for particle photon and gently push it over the pins of particle photon.

Then connect the one end of I2C cable HTS221 sensor and the other end to the I2C shield.

Connections are shown in the picture above.

The particle code for HTS221 can be downloaded from our github repository- DCUBE Community.

Here is the link for the same :

https://github.com/DcubeTechVentures/HTS221/blob/master/Particle/HTS221.ino

We have used two libraries for particle code, which are application.h and spark_wiring_i2c.h. Spark_wiring_i2c library is required to facilitate the I2C communication with the sensor.

You can also copy the code from here, it is given as follows:

// 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.

// HTS221

// This code is designed to work with the HTS221_I2CS I2C Mini Module

#include

#include

// HTS221 I2C address is 0x5F

#define Addr 0x5F

float humidity = 0.0;

float cTemp = 0.0;

float fTemp = 0.0;

int temp = 0;

void setup()

{

// Set variable

Particle.variable("i2cdevice", "HTS221");

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);

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Select average configuration register

Wire.write(0x10);

// Temperature average samples = 256, Humidity average samples = 512

Wire.write(0x1B);

// Stop I2C Transmission

Wire.endTransmission();

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Select control register1

Wire.write(0x20);

// Power ON, Continuous update, Data output rate = 1 Hz

Wire.write(0x85);

// Stop I2C Transmission

Wire.endTransmission();

delay(300);

}

void loop()

{

unsigned int data[2];

unsigned int val[4];

unsigned int H0, H1, H2, H3, T0, T1, T2, T3, raw;

// Humidity calliberation values

for(int i = 0; i < 2; i++)

{

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write((48 + i));

// Stop I2C Transmission

Wire.endTransmission();

// Request 1 byte of data

Wire.requestFrom(Addr, 1);

// Read 1 byte of data

if(Wire.available() == 1)

{

data[i] = Wire.read();

}

}

// Convert Humidity data

H0 = data[0] / 2;

H1 = data[1] / 2;

for(int i = 0; i < 2; i++)

{

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write((54 + i));

// Stop I2C Transmission

Wire.endTransmission();

// Request 1 byte of data

Wire.requestFrom(Addr,1);

// Read 1 byte of data

if(Wire.available() == 1)

{

data[i] = Wire.read();

}

}

// Convert Humiditydata

H2 = (data[1] * 256.0) + data[0];

for(int i = 0; i < 2; i++)

{

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write((58 + i));

// Stop I2C Transmission

Wire.endTransmission();

// Request 1 byte of data

Wire.requestFrom(Addr,1);

// Read 1 byte of data

if(Wire.available() == 1)

{

data[i] = Wire.read();

}

}

// Convert Humidity data

H3 = (data[1] * 256.0) + data[0];

// Temperature calliberation values

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write(0x32);

// Stop I2C Transmission

Wire.endTransmission();

// Request 1 byte of data

Wire.requestFrom(Addr,1);

// Read 1 byte of data

if(Wire.available() == 1)

{

T0 = Wire.read();

}

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write(0x33);

// Stop I2C Transmission

Wire.endTransmission();

// Request 1 byte of data

Wire.requestFrom(Addr,1);

// Read 1 byte of data

if(Wire.available() == 1)

{

T1 = Wire.read();

}

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write(0x35);

// Stop I2C Transmission

Wire.endTransmission();

// Request 1 byte of data

Wire.requestFrom(Addr, 1);

// Read 1 byte of data

if(Wire.available() == 1)

{

raw = Wire.read();

}

raw = raw & 0x0F;

// Convert the temperature calliberation values to 10-bits

T0 = ((raw & 0x03) * 256) + T0;

T1 = ((raw & 0x0C) * 64) + T1;

for(int i = 0; i < 2; i++)

{

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write((60 + i));

// Stop I2C Transmission

Wire.endTransmission();

// Request 1 byte of data

Wire.requestFrom(Addr,1);

// Read 1 byte of data

if(Wire.available() == 1)

{

data[i] = Wire.read();

}

}

// Convert the data

T2 = (data[1] * 256.0) + data[0];

for(int i = 0; i < 2; i++)

{

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write((62 + i));

// Stop I2C Transmission

Wire.endTransmission();

// Request 1 byte of data

Wire.requestFrom(Addr,1);

// Read 1 byte of data

if(Wire.available() == 1)

{

data[i] = Wire.read();

}

}

// Convert the data

T3 = (data[1] * 256.0) + data[0];

// Start I2C Transmission

Wire.beginTransmission(Addr);

// Send data register

Wire.write(0x28 | 0x80);

// Stop I2C Transmission

Wire.endTransmission();

// Request 4 bytes of data

Wire.requestFrom(Addr,4);

// Read 4 bytes of data

// humidity msb, humidity lsb, temp msb, temp lsb

if(Wire.available() == 4)

{

val[0] = Wire.read();

val[1] = Wire.read();

val[2] = Wire.read();

val[3] = Wire.read();

}

// Convert the data

humidity = (val[1] * 256.0) + val[0];

humidity = ((1.0 * H1) - (1.0 * H0)) * (1.0 * humidity - 1.0 * H2) / (1.0 * H3 - 1.0 * H2) + (1.0 * H0);

temp = (val[3] * 256) + val[2];

cTemp = (((T1 - T0) / 8.0) * (temp - T2)) / (T3 - T2) + (T0 / 8.0);

fTemp = (cTemp * 1.8 ) + 32;

// Output data to dashboard

Particle.publish("Relative humidity : ", String(humidity));

Particle.publish("Temperature in Celsius : ", String(cTemp));

Particle.publish("Temperature in Fahrenheit : ", String(fTemp));

delay(1000);

}

HTS221 can be employed in various consumer products like air humidifiers and refrigerators etc. This sensor also find its application in a wider arena including Smart home automation, Industrial automation, respiratory equipments, asset and goods tracking.