// i2c and u8g library for 1306 oled display

#include <Wire.h>
#include "U8glib.h"         

#define R_LOW 100           // 100k or 10k resistor, 1%, smd1206, 1/10 watt
#define R_HIGH 5000         // 5M or 500k  resistor, 1%, smd1206, 1/10 watt
#define AREF 1.1            // Aref pin voltage 
#define ADC_RESOLUTION 1023 // 10 bit ADC


U8GLIB_SSD1306_128X32 u8g(U8G_I2C_OPT_NONE);     // I2C OLED  Display instance
long half_Aref = 0; // adc 0 for reading half AREF = 550mv, should read 512
long ch_1 = 0;      // adc 1 for reading voltage divided ratio of external V1
long ch_2 = 0;      // adc 2 for reading voltage divided ratio of external V2
long ch_3 = 0;      // adc 3 for reading voltage divided ratio of external V3
float V1 = 0.0;     // calculating measured V1 from ADC ch 1
float V2 = 0.0;     // calculating measured V1 from ADC ch 2
float V3 = 0.0;     // calculating measured V1 from ADC ch 3
int dump = 0;       // discarding first adc conversion




/// Oled Loop Draw Function ///
void draw(void) 
{
 
 // set font for text
 u8g.setFont(u8g_font_5x8);
 u8g.drawStr( 0, 6, "Chan-1   Chan-2   Chan-3");
 // set font for number
 u8g.setFont(u8g_font_7x13B);
 // pring voltages measured on OLED
 u8g.setPrintPos(0, 20);u8g.print(V1,1);
 u8g.setPrintPos(45, 20);u8g.print(V2,1);
 u8g.setPrintPos(90, 20);u8g.print(V3,1);
 // set font and print units
 u8g.setFont(u8g_font_5x8);
 u8g.drawStr( 0, 32, "volts    volts    volts");
 
}
//////////////////////////////////////////////////////////

/// void setup ///

void setup(void) 
{

delay(500);                // delay for idk
analogReference(INTERNAL); // set 1.1v internal reference
delay(500);                // delay to stabilize aref voltage
u8g.setRot180();           // change display orientation

}

//////////////////////////////////////////////////////////

/// void loop ///

void loop(void) 
{

  delay(5); // delay before using I2C OLED
           // refresh i2c oled with updated value
  u8g.firstPage();  
  do {
    draw();
  } while( u8g.nextPage() );

delay(5);

// clear variables old value
half_Aref = 0;
ch_1 = 0;
ch_2 = 0;
ch_3 = 0;

/// Half AREF measurement ///    

dump = analogRead(A0); // discard first adc convertion
delay(10); // delay for channel switching stabilizaion

// take 150 samples and add them up
  for (int i=0; i<150;i++)
  {
    half_Aref = half_Aref+analogRead(A0);
//    delay(2);
  }

// average 150 samples for improved accuracy
  half_Aref = half_Aref/150;

//////////////////////////////////////////////////////////////////////

/// ADC Chan1 measurement for voltage V1 ///

dump = analogRead(A1); // discard first adc convertion
delay(10); // delay for channel switching stabilizaion

// take 150 samples and add them up
for (int i=0; i<150;i++)
  {
    ch_1 = ch_1+analogRead(A1);
//    delay(2);
  }

  ch_1 = ch_1/150;        // average 150 samples for improved accuracy
  ch_1 = ch_1- half_Aref; // calculate adc differential for measured V1 
  V1 = ch_1*((R_LOW+R_HIGH)/R_LOW)*(AREF)/ADC_RESOLUTION; // calc V1
///////////////////////////////////////////////////////////////////////
  
/// ADC Chan2 measurement for voltage V2 ///

dump = analogRead(A2); // discard first adc convertion
delay(10); // delay for channel switching stabilizaion

// take 150 samples and add them up
for (int i=0; i<150;i++)
  {
    ch_2 = ch_2+analogRead(A2);
//    delay(2);
  }

  ch_2 = ch_2/150;        // average 150 samples for improved accuracy
  ch_2 = ch_2- half_Aref; // calculate adc differential for measured V2
  V2 = ch_2*((R_LOW+R_HIGH)/R_LOW)*(AREF)/ADC_RESOLUTION; // calc V2
///////////////////////////////////////////////////////////////////////

/// ADC Chan3 measurement for voltage V3 ///

dump = analogRead(A3); // discard first adc convertion
delay(10); // delay for channel switching stabilizaion

// take 150 samples and add them up
for (int i=0; i<150;i++)
  {
    ch_3 = ch_3+analogRead(A3);
//    delay(2);
  }

  ch_3 = ch_3/150;        // average 150 samples for improved accuracy
  ch_3 = ch_3- half_Aref; // calculate adc differential for measured V3
  V3 = ch_3*((R_LOW+R_HIGH)/R_LOW)*(AREF)/ADC_RESOLUTION; // calc V3
///////////////////////////////////////////////////////////////////////


 
}

/// Void Loop ends here ///
///////////////////////////////////////////////////////////////////////