Ways to Improve ADC Measurement Accuracy and Resolution Part 1

In this video series we look at ways or tips to improve ADC measurement accuracy and resolution. In part 1 define what accuracy and resolution is and different types of error that can affect ADC measurements. We also look at the importance of using an accurate ADC reference voltage and why you want to scale the range of the signal you are measuring to the ADC's range.

//***************Arduino code used in video*******************************
/*This code demonstrates how to change the ADC voltage reference on an Arduino 
 * This was shown in an ADC tutorial on the ForceTronics YouTube Channel.
* This code is free and open for anybody to use at their own risk. 
*/

void setup() {
  Serial.begin(115200); //setup serial connection
  while(!Serial);
  analogReference(AR_EXTERNAL); //sets the ADC reference voltage to external (input is aRef pin)
  //analogReference(AR_DEFAULT); //set the ADC reference to default which is AVCC (uses power supply voltage or VCC as reference)
  //analogReference(AR_INTERNAL2V23); //uses 2.23V internal reference in SAMD21 uC
  analogReadResolution(12); //Set ADC to 12bit resolution, default is 10
  burn8Readings(); //make 8 readings but don't use them to ensure good reading after reference change
  delay(100);
  for(int i=0;i<500;i++) { //loop through a bunch of ADC readings and print them to serial plotter
    Serial.println(analogRead(A0)); //Make ADC measurement at A0
  }
  
}

void loop() {
  //don't need the loop
}

//This function makes 8 ADC measurements but does nothing with them
//Since after a reference change the ADC can return bad readings at first. This function is used to get rid of the first 
//8 readings to ensure an accurate one is displayed
void burn8Readings() {
  for(int i=0; i<8; i++) {
    analogRead(A0);
    delay(1);
  }
}

Tutorial on Digital to Analog Converters (DAC) and Example Using the MCP4728 Part 2

Two part tutorial on digital to analog converters (DAC). In part 2 we take a look at the capabilities of the MCP4728 which is a four channel DAC controlled via I2C. See the links below to access the code and get the PCB design from the video at PCBWay.

Link for PCB board at PCBWay: https://www.pcbway.com/project/shareproject/W08904ASW106_DAC_Example_Gerber.html

//**********Arduino Code with MCP4728 examples from video***************
/*
 * This code was written to demonstrate functions on the MCP4728 4 channel DAC for a video on the ForceTronics YouTube channel
 * This sketch leverages a library from GitHub made by Hideakitai, link to library: https://github.com/hideakitai/MCP4728
 * This code is public domain and free to anyone to use and modify with no restrictions at your own risk
 */

#include <Wire.h>
#include "MCP4728.h"

MCP4728 dac; //create object to library
//variables for wavform
int const sampleCount = 24; //samples to read to have a buffer
int signalSamples[sampleCount]; //create array to hold signal or waveform
float pi2 = 6.283; //value of pi times 2
const long clkFrequency = 400000; //I2C clock frequency
const uint8_t t1 = 3; //pin to setup test 1 fast sinewave
const uint8_t t2 = 4; //pin to setup test 2 sync'd sinewaves
const uint8_t LDAC = 5; //Output pin on MCU to control LDAC(not) pin on DAC

void setup() {
 //Create sinewave
 float in;
 float hBit = 2047.5;
 for (int i=0;i<sampleCount;i++)
 {
   in = pi2*(1/(float)sampleCount)*(float)i;
   signalSamples[i] = (int)(sin(in)*hBit + hBit);
 }

 pinMode(t1,INPUT_PULLUP); //configure test check pins
 pinMode(t2,INPUT_PULLUP); //configure test check pins
 pinMode(LDAC,OUTPUT); //configure test check pins
 digitalWrite(LDAC,HIGH); //turn DAC outputs off
 Wire.begin(); //start up I2C library
 Wire.setClock(clkFrequency); //set clock frequency for I2C comm
 dac.attatch(Wire, 13); //second argument is Arduino pin connected to LDAC(not), we are controlling LDAC manually so just entered pin we are not using
 dac.readRegisters(); //Used to read current settings from MCP4728
 dac.selectVref(MCP4728::VREF::VDD, MCP4728::VREF::VDD, MCP4728::VREF::VDD, MCP4728::VREF::VDD); //setup voltage ref for each DAC channel
 dac.selectPowerDown(MCP4728::PWR_DOWN::NORMAL, MCP4728::PWR_DOWN::NORMAL, MCP4728::PWR_DOWN::NORMAL, MCP4728::PWR_DOWN::NORMAL); //set power down mode, used for saving power
 dac.selectGain(MCP4728::GAIN::X1, MCP4728::GAIN::X1, MCP4728::GAIN::X1, MCP4728::GAIN::X1); //set gain on output amp
 //dac.enable(true); //enables the DAC outputs by controlling LDAC pin, but we are controlling LDAC manually in this example

  //perform test one
  if(!digitalRead(t1)) {
    digitalWrite(LDAC,LOW);
    //output sinewave as fast as we can
    for(;;) { //run test for infinitity 
      for(int j=0;j<sampleCount;j++) {
        dac.analogWrite(MCP4728::DAC_CH::A,signalSamples[j]);
      }
    }
  }
  else { //perform test 2 
    for(;;) {  //run test for infinitity 
      for(int j=0;j<sampleCount;j++) {
        int temp = j;
        digitalWrite(LDAC,HIGH); //turn outputs off
       // delay(1);
        dac.analogWrite(MCP4728::DAC_CH::A,signalSamples[temp]);
        temp += 8; //shift sigal 90 degrees
        if(temp > 23) temp -= sampleCount;
        dac.analogWrite(MCP4728::DAC_CH::B,signalSamples[temp]);
        temp += 8; //shift sigal 90 degrees
        if(temp > 23) temp -= sampleCount;
        dac.analogWrite(MCP4728::DAC_CH::C,signalSamples[temp]);
        temp += 8; //shift sigal 90 degrees
        if(temp > 23) temp -= sampleCount;
        dac.analogWrite(MCP4728::DAC_CH::D,signalSamples[temp]);
        digitalWrite(LDAC,LOW); //turn outputs on all four outputs at same time
       // delay(1);
      }
    }
  }
}

void loop() {
}