The Arduino UNO has five 10 bit Analog to Digital Converter pins (0-1023), but I needed higher resolution. I’m working with a I2C connected 16 bit 4 channel ADC from Adafruit called the ADS1115. 16 bits of resolution allows me to measure signed integers with values ranging from negative 32768 through positive 32767 (-5v to +5v). Although I’m running this single ended (measuring 4 separate inputs in respect to ground), it can also run in a 2 channel differential mode. This would measure the voltage difference between AIN0 and AIN1, and between AIN2 and AIN3. I’m multiplying the value being reported by the ADC by .000188 (188uV / bit) to get the voltage being supplied to the input.
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Click for a cool ADS1115 project, reading a current shunt!
The Raspberry Pi has no ADC, and can only read digital inputs, so this would be a nice addition, as the Pi does have a I2C interface. I’ll post an article on the code for doing this soon. Here is the code for the Arduino. Complete tutorial, connections, and library available at https://learn.adafruit.com/adafruit-4-channel-adc-breakouts
Raspberry Pi code and examples – https://github.com/adafruit/Adafruit-Raspberry-Pi-Python-Code
Arduino Code:
#include <Wire.h>
#include <Adafruit_ADS1015.h>
Adafruit_ADS1115 ads1115;
void setup(void)
{
Serial.begin(9600);
Serial.println(“Hello!”);
Serial.println(“Getting single-ended readings from AIN0..3”);
Serial.println(“ADC Range: +/- 6.144V (1 bit = 188uV)”);
ads1115.begin();
//ads1115.setGain(GAIN_TWOTHIRDS);
}
void loop(void)
{
int16_t adc0, adc1, adc2, adc3;
float volt0, volt1, volt2, volt3;
adc0 = ads1115.readADC_SingleEnded(0);
adc1 = ads1115.readADC_SingleEnded(1);
adc2 = ads1115.readADC_SingleEnded(2);
adc3 = ads1115.readADC_SingleEnded(3);
volt0 = adc0*0.000188;
volt1 = adc1*0.000188;
volt2 = adc2*0.000188;
volt3 = adc3*0.000188;
Serial.print(“AIN0: “);
Serial.print(adc0);
Serial.print(” “);
Serial.print(volt0, 4);
Serial.println(” vdc”);
Serial.print(“AIN1: “);
Serial.print(adc1);
Serial.print(” “);
Serial.print(volt1, 4);
Serial.println(” vdc”);
Serial.print(“AIN2: “);
Serial.print(adc2);
Serial.print(” “);
Serial.print(volt2, 4);
Serial.println(” vdc”);
Serial.print(“AIN3: “);
Serial.print(adc3);
Serial.print(” “);
Serial.print(volt3, 4);
Serial.println(” vdc”);
Serial.println(” “);
delay(1000);
}
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