ADS1115 ADC

ADS1115 is a precision, low power, 16 bit 860 SPS I2C analog to digital converter (ADC). It has internal reference, oscillator, and programmable comparator. ADS1115 modules are readily available at online markets like AliExpress and Adafruit

Figure 1. ADS1115 Adafruit module
( learn.adafruit.com/adafruit-4-channel-adc-breakouts/downloads).

An example to use ADS1115 with Raspberry Pi is shown in the following list.

// File: ads1115.cpp
// Description: analog input and analog output with ADS1115
// WebSite: http://cool-emerald.blogspot.com
// MIT License (https://opensource.org/licenses/MIT)
// Copyright (c) 2020 Yan Naing Aye

#include 
#include 
#include 
#include "ce_i2c.h"
using namespace std;

class ADS1115 {
public:
 ADS1115(uint8_t i2cBusNo, uint8_t i2cAddr);
 // ~ADS1115();
 void UpdateLastConversion();
 void StartConversion(uint8_t channel);
 // int16_t ContConvRead();
 uint8_t GetChannel();
 uint16_t GetConversionValue(uint8_t channel);
 float V(uint8_t channel);
private:
 uint8_t _bus;
 uint8_t _addr;
 uint8_t _channel;
 int16_t _ai[4]; 
};

// Get current channel
uint8_t ADS1115::GetChannel()
{
 return this->_channel;
}

// Get conversion value
uint16_t ADS1115::GetConversionValue(uint8_t channel)
{
 channel &= 0x03;
 return this->_ai[channel];
}

// Get voltage
float ADS1115::V(uint8_t channel)
{
 channel &= 0x03;
 // 4.096 / 32767 = 0.00012500
 float v = 0.00012500;
 v *= float(this->_ai[channel]);
    return v;
}

// addr : [0 - 1]
// channel : [0 - 3]
ADS1115::ADS1115(uint8_t i2cBusNo, uint8_t i2cAddr):_bus(i2cBusNo)
{
 this->_channel = 0;
 this->_addr = 0x48 | (i2cAddr & 0x01); // i2c address
}

// Read previous conversion result
void ADS1115::UpdateLastConversion()
{
 char d[] = { 0,0,0,0 };
 uint8_t v[] = {0,0};
 CE_I2C adc(this->_bus,this->_addr);
 // first byte in i2c wr is the address reg
 d[0] = 0x00; // point to conversion register
 adc.Write(d, 1); 
 // read 2 bytes conversion reg value 
 adc.Read(d, 2); 
 adc.Close();
 v[1] = d[0];
 v[0] = d[1];
 this->_ai[this->_channel] = *(int16_t*)(v); 
}

// start conversion of next channel
void ADS1115::StartConversion(uint8_t channel)
{
 char d[] = { 0,0,0,0 };
 CE_I2C adc(this->_bus,this->_addr);
 // Choose channel to read
 // first byte in i2c wr is the address reg
 d[0] = 0x01; // point to control reg
 // followed by 2 bytes (LSB MSB) 16 bit control reg
 // | OS | MUX[2:0] | PGA[2:0] | Mode |
 // | 1  | 1 c1 c0  | 001      | 1    |
 // OS = 1 start single shot conversion
 // MUX[2:0] 100 = A0 to GND, 101 = A1 to GND, 110 = A2 to GND, 111 = A31 to GND
 // PGA[2:0] 001 +/- 4.096 V default
 // MODE = 1 single shot mode - default
 d[1] = 0xC3; // MSB first
 // | DR[2:0] | COMP_MODE | COMP_POL | COMP_LAT | COMP_QUE[1:0] |
 // |   111   |   0       |  0       |    0     |   11          |
 // DR[2:0] = 111 for data rate of 860 SPS
 // COMP_MODE = 0 default - traditional comparator 
 // COMP_POL = 0 default - active low
 // COMP_LAT = 0 default - non latching
 // COMP_QUE[1:0] = 11 default - high impedance ALERT/RDY pin
 d[2] = 0xE3;
 //--------------------------------------------------------------------
 // select next channel
 this->_channel = channel & 0x03; // get adc channel
 d[1] |= (this->_channel << 4);
 //--------------------------------------------------------------------
 adc.Write(d, 3); // set control reg to start conversion of next channel
 adc.Close();
}

int main()
{
 int16_t v;
 ADS1115 a(1,0);
    while(1)
    {    
  for(uint8_t i=0;i<4;i++){
   a.StartConversion(i);
   usleep(256000);
   a.UpdateLastConversion();
   printf("C%d = %1.3f V, ",i,a.V(i));
  }
  printf("\n");
 }
    return 0;
}

The source code are also available at

https://github.com/yan9a/rpi/tree/master/bus/ads1115