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CPS120 is a high quality and low cost capacitive absolute pressure sensor with fully compensated output. It consumes very less power and comprises of an ultra small Micro-Electro-Mechanical Sensor(MEMS) for pressure measurement. A sigma-delta based ADC is also embodied in it to accomplish the requirement of compensated output.

In this tutorial the interfacing of the CPS120 sensor module with particle photon has been illustrated. To read the pressure 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:

1. CPS120

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 CPS120 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 Pressure 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>

// CPS120 I2C address is 0x28(40)

#define Addr 0x28

double temperature = 0.0, pressure = 0.0;

void setup()

{

// Set variable

Particle.variable("i2cdevice", "CPS120");

Particle.variable("pressure", pressure);

Particle.variable("temperature", temperature);

// Initialise I2C communication as MASTER

Wire.begin();

// Initialise serial communication, set baud rate = 9600

Serial.begin(9600);

} void loop()

{

unsigned int data[4];

// Start I2C Transmission

Wire.beginTransmission(Addr);

delay(10);

// Stop I2C Transmission

Wire.endTransmission();

// Request 4 byte of data

Wire.requestFrom(Addr, 4);

// Read 4 bytes of data

// pressure msb, pressure 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 values

pressure = ((((data[0] & 0x3F) * 265 + data[1]) / 16384.0 ) * 90.0 ) + 30.0 ;

cTemp = ((((data[2] * 256) + (data[3] & 0xFC)) / 4.0 ) * (165.0 / 16384.0)) - 40.0;

fTemp = cTemp * 1.8 + 32;

// Output data to dashboard

Particle.publish("Pressure is : ", String(pressure));

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:

CPS120 has a variety of applications. It can be employed in portable and stationary barometers, altimeters etc. Pressure is an important parameter to determine the weather conditions and considering that this sensor can be installed at weather stations too. It can be incorporated in air contol systems as well as vacuum systems.

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