MPL3115A2 pressure sensor and Beaglebone example in C

19th July 2019

953

In this article we look at an MPL3115A2 connected to a Beaglebone first of all lets look at the sensor.

The MPL3115A2 is a compact, piezoresistive, absolute pressure sensor with an I2C digital interface. MPL3115A2 has a wide operating range of 20 kPa to 110 kPa, a range that covers all surface elevations on earth. The MEMS is temperature compensated utilizing an on-chip temperature sensor. The pressure and temperature data is fed into a high resolution ADC to provide fully compensated and digitized outputs for pressure in Pascals and temperature in °C.

This typically comes in a breakout such as the one in the breakout below

Parts Required

Name	Link
Beaglebone	BeagleBone Black TI AM3358 Cortex-A8 development BB-Black Rev.C
MPL3115A2	MPL3115A2 I2C Intelligent Temperature Pressure Altitude Sensor V2.0 for Arduino
Connecting wire	Dupont line 120pcs 20cm male to male + male to female and female to female jumper wire

Schematic/Connection

Code Example

This is a controleverything example. This is the C example from https://github.com/ControlEverythingCommunity/MPL3115A2

Source code

#include <stdio.h>
#include <stdlib.h>
#include <linux/i2c-dev.h>
#include <sys/ioctl.h>
#include <fcntl.h>
 
void main() 
{
	// Create I2C bus
	int file;
	char *bus = "/dev/i2c-2";
	if((file = open(bus, O_RDWR)) < 0)
	{
		printf("Failed to open the bus. \n");
		exit(1);
	}
	// Get I2C device, MPL3115A2 I2C address is 0x60(96)
	ioctl(file, I2C_SLAVE, 0x60);
 
	// Select control register(0x26)
	// Active mode, OSR = 128, altimeter mode(0xB9)
	char config[2] = {0};
	config[0] = 0x26;
	config[1] = 0xB9;
	write(file, config, 2);
	// Select data configuration register(0x13)
	// Data ready event enabled for altitude, pressure, temperature(0x07)
	config[0] = 0x13;
	config[1] = 0x07;
	write(file, config, 2);
	// Select control register(0x26)
	// Active mode, OSR = 128, altimeter mode(0xB9)
	config[0] = 0x26;
	config[1] = 0xB9;
	write(file, config, 2);
	sleep(1);
 
	// Read 6 bytes of data from address 0x00(00)
	// status, tHeight msb1, tHeight msb, tHeight lsb, temp msb, temp lsb
	char reg[1] = {0x00};
	write(file, reg, 1);
	char data[6] = {0};
	if(read(file, data, 6) != 6)
	{
		printf("Error : Input/Output error \n");
		exit(1);
	}
 
	// Convert the data
	int tHeight = ((data[1] * 65536) + (data[2] * 256 + (data[3] & 0xF0)) / 16);
	int temp = ((data[4] * 256) + (data[5] & 0xF0)) / 16;
	float altitude = tHeight / 16.0;
	float cTemp = (temp / 16.0);
	float fTemp = cTemp * 1.8 + 32;
 
	// Select control register(0x26)
	// Active mode, OSR = 128, barometer mode(0x39)
	config[0] = 0x26;
	config[1] = 0x39;
	write(file, config, 2);
	sleep(1);
 
	// Read 4 bytes of data from register(0x00)
	// status, pres msb1, pres msb, pres lsb
	reg[0] = 0x00;
	write(file, reg, 1);
	read(file, data, 4);
 
	// Convert the data to 20-bits
	int pres = ((data[1] * 65536) + (data[2] * 256 + (data[3] & 0xF0))) / 16;
	float pressure = (pres / 4.0) / 1000.0;
 
	// Output data to screen
	printf("Pressure : %.2f kPa \n", pressure);
	printf("Altitude : %.2f m \n", altitude);
	printf("Temperature in Celsius : %.2f C \n", cTemp);
	printf("Temperature in Fahrenheit : %.2f F \n", fTemp);
 
	exit(0);
}