Raspberry Pi HTS221 Relative Humidity and Temperature Sensor Python 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 a java code using Raspberry Pi.

1. Raspberry Pi

2. HTS221

3. I²C Cable

4. I²C Shield for Raspberry Pi

5. Ethernet Cable

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.

The python code for HTS221 can be downloaded from our github repository- Dcube Store.

Here is the link for the same :

https://github.com/DcubeTechVentures/HTS221/blob/master/Python/HTS221.py

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

https://pypi.python.org/pypi/smbus-cffi/0.5.1

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.

import smbus

import time

# Get I2C bus

bus = smbus.SMBus(1)

# HTS221 address, 0x5F(95)

# Select average configuration register, 0x10(16)

# 0x1B(27) Temperature average samples = 256, Humidity average samples = 512

bus.write_byte_data(0x5F, 0x10, 0x1B)

# HTS221 address, 0x5F(95)

# Select control register1, 0x20(32)

# 0x85(133) Power ON, Continuous update, Data output rate = 1 Hz

bus.write_byte_data(0x5F, 0x20, 0x85)

time.sleep(0.5)

# HTS221 address, 0x5F(95)# Read Calibration values from non-volatile memory of the device

# Humidity Calibration values

# Read data back from 0x30(48), 1 byte

val = bus.read_byte_data(0x5F, 0x30)

H0 = val / 2

# Read data back from 0x31(49), 1 byte

val = bus.read_byte_data(0x5F, 0x31)

H1 = val /2

# Read data back from 0x36(54), 2 bytes

val0 = bus.read_byte_data(0x5F, 0x36)

val1 = bus.read_byte_data(0x5F, 0x37)

H2 = ((val1 & 0xFF) * 256) + (val0 & 0xFF)

# Read data back from 0x3A(58), 2 bytes

val0 = bus.read_byte_data(0x5F, 0x3A)

val1 = bus.read_byte_data(0x5F, 0x3B)

H3 = ((val1 & 0xFF) * 256) + (val0 & 0xFF)

# Temperature Calibration values

# Read data back from 0x32(50), 1 byte

T0 = bus.read_byte_data(0x5F, 0x32)

T0 = (T0 & 0xFF)

# Read data back from 0x32(51), 1 byte

T1 = bus.read_byte_data(0x5F, 0x33)

T1 = (T1 & 0xFF)

# Read data back from 0x35(53), 1 byte

raw = bus.read_byte_data(0x5F, 0x35)

raw = (raw & 0x0F)

# Convert the temperature Calibration values to 10-bits

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

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

# Read data back from 0x3C(60), 2 bytes

val0 = bus.read_byte_data(0x5F, 0x3C)

val1 = bus.read_byte_data(0x5F, 0x3D)

T2 = ((val1 & 0xFF) * 256) + (val0 & 0xFF)

# Read data back from 0x3E(62), 2 bytes

val0 = bus.read_byte_data(0x5F, 0x3E)

val1 = bus.read_byte_data(0x5F, 0x3F)

T3 = ((val1 & 0xFF) * 256) + (val0 & 0xFF)

# Read data back from 0x28(40) with command register 0x80(128), 4 bytes

# humidity msb, humidity lsb, temp msb, temp lsb

data = bus.read_i2c_block_data(0x5F, 0x28 | 0x80, 4)

# Convert the data

humidity = (data[1] * 256) + data[0]

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

temp = (data[3] * 256) + data[2]

if temp > 32767 :

temp -= 65536

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

fTemp = (cTemp * 1.8 ) + 32

# Output data to screen

print "Relative Humidity : %.2f %%" %humidity

print "Temperature in Celsius : %.2f C" %cTemp

print "Temperature in Fahrenheit : %.2f F" %fTemp

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.