DIY

// *********************************************************
// Program:   two chanel voltmeter with thermometer
// Date:      01/09/2018
// Version:   1.0
// Author:    Elvis Baketa
// Description: 
// *********************************************************

#include <Arduino.h>
#include <Wire.h>
#include <U8g2lib.h>

// WHITE OLED LCD 0.96" 128X64 I2C
U8G2_SSD1306_128X64_NONAME_F_HW_I2C u8g2(U8G2_R0, /* reset=*/ U8X8_PIN_NONE);

unsigned long startTime;
unsigned long finishTime;

int updateDisplay = 0;
int samples = 16;
float resolution = 4096.0;
float voltageReference = 4.096;
float seriesResistor = 47000.00;

int analogValueCH0[16];
int analogValueCH1[16];
int analogValueCH2[16];
unsigned int averageAnalogValueCH0;
unsigned int averageAnalogValueCH1;
unsigned int averageAnalogValueCH2;
float voltageCH0 = 0.000;
float voltageCH1 = 0.000;
float voltageCH2 = 0.000;
float averageVoltageCH1 = 0.000;
float averageVoltageCH2 = 0.000;

float resistance = 0.000;
float temperature = 0.000;
float averageTemperature = 0.000;

void setup() {
  // put your setup code here, to run once:
  analogReference(EXTERNAL);
  u8g2.begin();
}

void loop() {
  // put your main code here, to run repeatedly:
  updateDisplay++;
  
  // read chanel one
  for(int i = 0; i < samples; i++) {
    analogValueCH0[i] = analogRead(A0);
    delay(1);
  }
  for(int l = 0; l < samples; l++) {
    averageAnalogValueCH0 += analogValueCH0[l];
  }
  averageAnalogValueCH0 /= 4;
  voltageCH0 = averageAnalogValueCH0 * (voltageReference / resolution);
  averageAnalogValueCH0 = 0;
  // convert volts to resistance
  resistance = voltageReference / voltageCH0 - 1;
  resistance = 1 / resistance;
  resistance = seriesResistor * resistance;
  // convert resistance to temperature in Kelvin
  temperature = log(resistance / seriesResistor);
  temperature = temperature * (1 / float(3435));
  temperature = temperature + (1 / (25 + 273.15));
  temperature = 1 / temperature;
  // convert Kelvin to Celsius
  // T(°C) = T(°K) - 273.15
  temperature = temperature - 273.15;
  averageTemperature += temperature;
  
  // read chanel two
  for(int j = 0; j < samples; j++) {
    analogValueCH1[j] = analogRead(A1);
    delay(1);
  }
  for(int m = 0; m < samples; m++) {
    averageAnalogValueCH1 += analogValueCH1[m];
  }
  averageAnalogValueCH1 /= 4;
  voltageCH1 = averageAnalogValueCH1 * (voltageReference / resolution);
  voltageCH1 *= 10;
  averageVoltageCH1 += voltageCH1;
  averageAnalogValueCH1 = 0;
  
  // read chanel three
  for(int k = 0; k < samples; k++) {
    analogValueCH2[k] = analogRead(A2);
    delay(1);
  }
  for(int n = 0; n < samples; n++) {
    averageAnalogValueCH2 += analogValueCH2[n];
  }
  averageAnalogValueCH2 /= 4;
  voltageCH2 = averageAnalogValueCH2 * (voltageReference / resolution);
  voltageCH2 *= 10;
  averageVoltageCH2 += voltageCH2;
  averageAnalogValueCH2 = 0;

  if(updateDisplay > 4) {
    // display data
    u8g2.clearBuffer();
    u8g2.setFont(u8g2_font_profont22_tf);
    averageTemperature /= updateDisplay;
    u8g2.setCursor(0, 16);
    u8g2.print("T ");
    u8g2.print(averageTemperature);
    u8g2.print(char(176));
    u8g2.print("C");
    averageVoltageCH1 /= updateDisplay;
    u8g2.setCursor(0, 32);
    u8g2.print("CH1 ");
    u8g2.print(averageVoltageCH1);
    u8g2.print("V");
    averageVoltageCH2 /= updateDisplay;
    u8g2.setCursor(0, 48);
    u8g2.print("CH2 ");
    u8g2.print(averageVoltageCH2);
    u8g2.print("V");
    u8g2.setCursor(0, 64);
    finishTime = millis() - startTime;
    u8g2.print(finishTime);
    u8g2.print(" ms");
    u8g2.sendBuffer();
    averageTemperature = 0.000;
    averageVoltageCH1 = 0.000;
    averageVoltageCH2 = 0.000;
    updateDisplay = 0;
    startTime = millis();
  }
}