/* Adjustable Load

   David Johnson-Davies - www.technoblogy.com - 24th March 2016
   ATtiny84 @ 1 MHz (internal oscillator; BOD disabled)
   
   CC BY 4.0
   Licensed under a Creative Commons Attribution 4.0 International license: 
   http://creativecommons.org/licenses/by/4.0/
*/

// Seven-segment definitions
const int charArrayLen = 12;
char charArray[] = {
//  ABCDEFG  Segments
  0b1111110, // 0
  0b0110000, // 1
  0b1101101, // 2
  0b1111001, // 3
  0b0110011, // 4
  0b1011011, // 5
  0b1011111, // 6
  0b1110000, // 7
  0b1111111, // 8
  0b1111011, // 9
  0b0000000, // 10  Space
  0b0000001  // 11  Dash
};

const int Dash = 11;
const int Space = 10;
const int Ndigits = 3;                       // Number of digits

volatile int Current = 0;                    // Current in mA
volatile unsigned long Charge = 0;           // Charge in mA-seconds

volatile char Buffer[] = {Dash, Dash, Dash};
int digit = 0;
int DP = -1;  // Decimal point position 0 or 1

// Pin assignments
char Digits[] = {PIN_B0, PIN_B1, PIN_B2};

// Display multiplexer **********************************************

void DisplayNextDigit() {
  static int LastReading;
  DDRB = 0;                                  // Make all digits inputs
  digit = (digit+1) % (Ndigits+1);
  if (digit < Ndigits) {
    char segs = charArray[Buffer[digit]];
    if (digit == DP) {                         // Decimal point
      DDRB = DDRB | 0x04;
      PORTB = PORTB & 0xFB;
    }
    PORTA = ~segs & 0x7F;                    // Mask out PA7 for ADC
    DDRA = segs & 0x7F;
    DDRB = DDRB | 1<<Digits[digit];          // Make digit an output
    PORTB = PORTB | 1<<Digits[digit];        // Take digit bit high
  } else {
    DDRA = 0;                                // All inputs
    PORTA = 0;
    // Read analogue input
    Current = (ReadADC()*13)/14;
    // If current zero, display charge
    if (Current == 0) {
      int mAh = Charge/3600;
      if (mAh < 1000) Display(mAh, -1); else Display(mAh/10, 0);
    } else {
      // Add hysteresis to stop display jumping
      if (abs(LastReading - Current)>=10) {
        Display(Current/10, 0);
        LastReading = Current;
      }
    }
  }
}

// Display a three digit decimal number with decimal point
void Display (int number, int point) {
  int blank = false, digit, j=100;
  if (point != 0) blank = true;
  for (int d=0; d<Ndigits ; d++) {
    digit = (number/j) % 10;
    if (digit==0 && blank && d!=2) Buffer[d] = Space;
    else {
      Buffer[d] = digit;
      blank = false;
    }
    j = j / 10;
  }
  DP = point;
}

// Timer 0 interrupt - multiplexes display and does ADC conversion
ISR(TIM0_COMPA_vect) {
  DisplayNextDigit();
}

// Timer 1 interrupt - counts mAh
ISR(TIM1_COMPA_vect) {
  Charge = Charge + Current;
  if (Current != 0) DP = DP ^ 0xFF;   // Flash decimal point
}

// Do ADC conversions **********************************************

int ReadADC () {
  unsigned char low, high;
  ADCSRA = ADCSRA | 1<<ADSC;           // Start
  do ; while (ADCSRA & 1<<ADSC);       // Wait while conversion in progress
  return ADC;
}

// Setup **********************************************

void setup() {
  OSCCAL = 101;
  // Set up Timer/Counter0 to multiplex the display
  TCCR0A = 2<<WGM00;                   // CTC mode
  TCCR0B = 0<<WGM02 | 3<<CS00;         // Divide by 64
  OCR0A = 49;                          // Divide by 50 for 312.5Hz interrupt
  TIMSK0 = 1<<OCIE0A;                  // Enable compare match interrupt
 // Set up Timer/Counter1 to count seconds
  TCCR1A = 0<<WGM10;
  TCCR1B = 1<<WGM12 | 3<<CS10;         // Divide by 64
  OCR1A = 15624;                       // Divide by 15625 for 1Hz interrupt
  TIMSK1 = 1<<OCIE1A;                  // Enable compare match interrupt
  // Set up ADC on ADC7 (PA7)
  ADMUX = 2<<REFS0 | 7<<MUX0;          // 1.1V ref, ADC7 (PA7)
  ADCSRA = 1<<ADEN | 4<<ADPS0;         // Enable ADC, 62.5kHz clock
}

// Everything done under interrupt
void loop () {
}