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HYT939 is a digital humidity sensor which works on I2C communication protocol. Humidity is a pivotal parameter when it comes to medical systems and laboratories, So in order to accomplish these goals we tried to interface HYT939 with raspberry pi. In this tutorial the interfacing of the HYT939 sensor module with particle photon has been illustrated.

To read the humidity values, we have used particle photon with an I2c adapter.This I2C adapter makes the connection to the sensor module easy and more reliable.Particle photon is a board which facilitates sending and receiving data from website, that is supporting the most basic feature of Internet Of Things(IoT).

Step 1: Hardware Required:

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

1. HYT939

2. Particle Photon

3. I2C Cable

4. I2C Shield For particle Photon

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 HYT939 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 Humidity 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:

#include<application.h>

#include<spark_wiring_i2c.h>

// HYT939 I2C address is 0x28(40)

#define Addr 0x28

double humidity = 0.0, cTemp = 0.0, fTemp = 0.0;

void setup()

{

// Set variable

Particle.variable("i2cdevice", "HYT939");

Particle.variable("cTemp", cTemp);

Particle.variable("humidity", humidity);

// Initialise I2C communication as MASTER

Wire.begin();

// Initialise Serial Communication

Serial.begin(9600);

delay(300);

} void loop()

{

unsigned int data[4];

// Start I2C transmission

Wire.beginTransmission(Addr);

// Send normal mode command

Wire.write(0x80);

// Stop I2C transmission

Wire.endTransmission();

delay(300);

// Request 4 bytes of data from the device

Wire.requestFrom(Addr, 4);

// Read 4 bytes of data

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

if(Wire.available() == 4)

{

data[0] = Wire.read();

data[1] = Wire.read();

data[2] = Wire.read();

data[3] = Wire.read();

}

// Convert the data to 14-bits

humidity = (((data[0] & 0x3F) * 256.0) + data[1]) * (100.0 / 16383.0);

cTemp = (((data[2] * 256.0) + (data[3] & 0xFC)) / 4) * (165.0 / 16383.0) - 40;

fTemp = (cTemp * 1.8) + 32;

// Output data to dashboard

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

delay(1000);

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

delay(1000);

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

delay(1000);

}

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:

HYT939 being an efficient digital humidity sensor are employed in Medical systems, Autoclaves. Pressure dew point measurement and Drying systems also find the usage of this sensor module.In various Laboratories where appropriate humidity level is a pivotal parameter for conducting experiments, this sensor can be deployed there for humidity measurements.