Beaglebone and ADS1115 analog-to-digital converter C example

In this example we connect an ADS1115 analog-to-digital converters to a Beaglebone. The code example will be in C

Lets look at the ADS1115.

The ADS1115 is a precision, low-power, 16-bit, I²C-compatible, analog-to-digital converters (ADCs) offered in an ultra-small, leadless, X2QFN-10 package, and a VSSOP-10 package. The ADS1115 incorporates a low-drift voltage reference and an oscillator.

The ADS1115 also incorporate a programmable gain amplifier (PGA) and a digital comparator. These features, along with a wide operating supply range, make the ADS1115 well suited for power- and space-constrained, sensor measurement applications.

The ADS1115 performs conversions at data rates up to 860 samples per second (SPS). The PGA offers input ranges from ±256 mV to ±6.144 V, allowing precise large- and small-signal measurements. The ADS1115 features an input multiplexer (MUX) that allows two differential or four single-ended input measurements. Use the digital comparator in the ADS1115 for under- and overvoltage detection.

The ADS1115 operates in either continuous-conversion mode or single-shot mode. The devices are automatically powered down after one conversion in single-shot mode; therefore, power consumption is significantly reduced during idle periods.

Connection

In this example I had connected the sensor to the Beaglebone I2C2 SCL and SDA pins

Parts List

Code

Save the following as ADS1115.c

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, ADS1115 I2C address is 0x48(72)
	ioctl(file, I2C_SLAVE, 0x48);
 
	// Select configuration register(0x01)
	// AINP = AIN0 and AINN = AIN1, +/- 2.048V
	// Continuous conversion mode, 128 SPS(0x84, 0x83)
	char config[3] = {0};
	config[0] = 0x01;
	config[1] = 0x84;
	config[2] = 0x83;
	write(file, config, 3);
	sleep(1);
 
	// Read 2 bytes of data from register(0x00)
	// raw_adc msb, raw_adc lsb
	char reg[1] = {0x00};
	write(file, reg, 1);
	char data[2]={0};
	if(read(file, data, 2) != 2)
	{
		printf("Error : Input/Output Error \n");
	}
	else 
	{
		// Convert the data
		int raw_adc = (data[0] * 256 + data[1]);
		if (raw_adc > 32767)
		{
			raw_adc -= 65535;
		}
 
		// Output data to screen
		printf("Digital Value of Analog Input: %d \n", raw_adc);
	}
}

Output

Run the above example by opening a terminal and typing in

Compile the c program.

$>gcc ADS1115.c -o ADS1115

Run the c program.

$>./ADS1115

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