/**
 * Attempting to measure current with a DIY shunt resistor,
 * and voltage amplification via an opamp.
 *
 *                                     +--------+
 *        (PCINT5/~RESET/ADC0/dW) PB5  | 1    8 | VCC
 * (PCINT3/XTAL1/CLKI/~OC1B/ADC3) PB3  | 2    7 | PB2 (SCK/USCK/SCL/ADC1/T0/INT0/PCINT2)
 *  (PCINT4/XTAL2/CLKO/OC1B/ADC2) PB4  | 3    6 | PB1 (MISO/DO/AIN1/OC0B/OC1A/PCINT1)
 *                                GND  | 4    5 | PB0 (MOSI/DI/SDA/AIN0/OC0A/~OC1A/AREF/PCINT0)
 *                                     +--------+
 **/

#include <TinyWireM.h>
#include <Tiny4kOLED.h>

float v1;
float v2;
float voltage;
float resistance = 1000;
float current;
float power;

void setup() {
  // Start the I2C communications
  oled.begin();

  // Two fonts: FONT8X16 and FONT6X8
  oled.setFont(FONT8X16);

  // To clear all the memory, clear both rendering frames:
  oled.clear();
  oled.switchRenderFrame();
  oled.clear();
  oled.switchRenderFrame();
}

void loop() {
  // Take the measurments
  v1 = (analogRead(3) * 5 / 1023);
  v2 = (analogRead(4) * 5 / 1023);

  voltage = v1 - v2;
  current = voltage / resistance;
  power = current * voltage;

  // Write the measurements
  // The SSD1306 refers to 8 rows of pixels as a 'page'
  
  // page 0: Voltage
  oled.setCursor(0,0);                 
  oled.print("Voltage: ");   
  oled.print(voltage);   
  oled.println(" V");

  // page 1: Current
  oled.setCursor(0,2);
  oled.print("Current: ");   
  oled.print(current * 1000);   
  oled.println(" mA");   

  // page 2: Power
  oled.setCursor(0,4);
  oled.print("Power:   ");   
  oled.print(power);   
  oled.println(" W");   

  oled.on();

  delay(500);
  }