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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 a java code using Raspberry Pi.

Step 1: What You Need..!!

1. Raspberry Pi

2. HTS221

LINK : https://www.controleverything.com/content/Temperature?sku=HTS221_I2CS

3. I²C Cable

LINK : https://www.controleverything.com/content/I2C-Cables?sku=I2CAFF3

4. I²C Shield for Raspberry Pi

LINK : https://www.controleverything.com/content/I2C-Master?sku=TOUTPI2

5. Ethernet Cable

Step 2: Connections:

Take a I2C shield for raspberry pi and gently push it over the gpio pins of raspberry pi.

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

Also connect the Ethernet cable to the pi or you can use a WiFi module.

Connections are shown in the picture above.

Step 3: Code:

The python code for HTS221 can be downloaded from our github repository- ControlEverythingCommunity

Here is the link for the same :

https://github.com/ControlEverythingCommunity/HTS2...

The datasheet of HTS221 can be found here:

http://www.st.com/web/en/resource/technical/docume...

We have used pi4j library for java code, the steps to install pi4j on raspberry pi is described here:

http://pi4j.com/install.html

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 available from ControlEverything.com.

// https://www.controleverything.com/content/Humidit...


import com.pi4j.io.i2c.I2CBus;

import com.pi4j.io.i2c.I2CDevice;

import com.pi4j.io.i2c.I2CFactory;

import java.io.IOException;

public class HTS221{ public static void main(String args[]) throws Exception

{

// Create I2CBus

I2CBus bus = I2CFactory.getInstance(I2CBus.BUS_1);

// Get I2C device, HTS221 I2C address is 0x5F(95)

I2CDevice device = bus.getDevice(0x5F);

// Select average configuration register

// Temperature average samples = 16, humidity average samples = 32

device.write(0x10, (byte)0x1B);

// Select control register1

// Power on, block data update, data rate o/p = 1 Hz

device.write(0x20, (byte)0x85);

Thread.sleep(500);

// Read Calibration values from the non-volatile memory of the device

// Humidity Calibration values

byte[] val = new byte[2];

// Read 1 byte of data from address 0x30(48)

val[0] = (byte)device.read(0x30);

// Read 1 byte of data from address 0x31(49)

val[1] = (byte)device.read(0x31);

int H0 = (val[0] & 0xFF) / 2;

int H1 = (val[1] & 0xFF) / 2;

// Read 1 byte of data from address 0x36(54)

val[0] = (byte)device.read(0x36);

// Read 1 byte of data from address 0x37(55)

val[1] = (byte)device.read(0x37);

int H2 = ((val[1] & 0xFF) * 256) + (val[0] & 0xFF);

// Read 1 byte of data from address 0x3A(58)

val[0] = (byte)device.read(0x3A);

// Read 1 byte of data from address 0x3B(59)

val[1] = (byte)device.read(0x3B);

int H3 = ((val[1] & 0xFF) * 256) + (val[0] & 0xFF);

// Temperature Calibration values

// Read 1 byte of data from address 0x32(50)

int T0 = ((byte)device.read(0x32) & 0xFF);

// Read 1 byte of data from address 0x33(51)

int T1 = ((byte)device.read(0x33) & 0xFF);

// Read 1 byte of data from address 0x35(53)

int raw = ((byte)device.read(0x35) & 0x0F);

// Convert the temperature Calibration values to 10-bits

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

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

// Read 1 byte of data from address 0x3C(60)

val[0] = (byte)device.read(0x3C);

// Read 1 byte of data from address 0x3D(61)

val[1] = (byte)device.read(0x3D);

int T2 = ((val[1] & 0xFF) * 256) + (val[0] & 0xFF);

// Read 1 byte of data from address 0x3E(62)

val[0] = (byte)device.read(0x3E);

// Read 1 byte of data from address 0x3F(63)

val[1] = (byte)device.read(0x3F);

int T3 = ((val[1] & 0xFF) * 256) + (val[0] & 0xFF);

// Read 4 bytes of data

// hum msb, hum lsb, temp msb, temp lsb

byte[] data = new byte[4]; device.read(0x28 | 0x80, data, 0, 4);

// Convert the data

int hum = ((data[1] & 0xFF) * 256) + (data[0] & 0xFF);

int temp = ((data[3] & 0xFF) * 256) + (data[2] & 0xFF);

if(temp > 32767)

{

temp -= 65536;

}

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

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

double fTemp = (cTemp * 1.8 ) + 32;

// 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 Fahrenheit : %.2f F %n", fTemp);

}

}

Step 4: Applications:

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.