11.2: Assignment

This exercise involves a considerable amount of wiring and a non-trivial amount of code. There are a lot of things that can go wrong if you just dive in and try to do everything at once. For example, if a segment or an entire digit fails to light, how do know whether the problem is in the hardware or in the software? Debugging both simultaneously is no minor task. It is better to make sure that chunks of the code work as expected first, then build on that. For example, you might just code the chunk that lights one display then expand to a multiplexed display. Consider something like this:

// Port B.0:2 for 7 segment mux
#define DIGIT1   0x01
#define DIGIT10  0x02
#define DIGIT100 0x04
#define DIGIT111 0x07

#define FSRMASK  0x08

unsigned char numeral[]={
   //ABCDEFG,dp
   0b00000011,   // 0
   0b10011111,   // 1 
   0b00100101,   // 2
   0b00001101,   // 3
   0b10011001,
   0b01001001,
   0b01000001,
   0b00011111,
   0b00000001,
   0b00011001,   // 9
   0b11111111,   // blank
   0b01100001,   // E
   0b01110011,   // r
   0b00001001,   // g
   0b00111001    // o  
};

#define LETTER_BLANK  10
#define LETTER_E      11
#define LETTER_R      12
#define LETTER_G      13
#define LETTER_O      14
#define MSG_ERR       -2

void loop()
{
   // try a bunch of different things...
   DisplayValue(123);
   DisplayValue(456);
   DisplayValue(12);
   DisplayValue(3);
   DisplayValue(100);
   DisplayValue(-2);
   DisplayValue(50);
}

void DisplayValue( int v )
{
   unsigned char i, h, t, u; // hundreds, tens, units

   if( (v <= MSG_ERR) || (v > 999) ) // error code
   {
      h = LETTER_E;
      t = u = LETTER_R;
   }
   else
   {
      u = v%10;
      v = v/10;
      t = v%10;
      h = v/10;
   }

   // display the value for approx 1 sec (66x15msec)
   for( i=0; i<66; i++ )
   {
      // clear all displays then activate the desired digit
      PORTB |= DIGIT111;
      PORTD = numeral[h];
      PORTB &= ~DIGIT100;
      delay(5);

      PORTB |= DIGIT111;
      PORTD = numeral[t];
      PORTB &= ~DIGIT10;
      delay(5);

      PORTB |= DIGIT111;
      PORTD = numeral[u];
      PORTB &= ~DIGIT1;
      delay(5);   
   }
  
   // clear display
   PORTB |= DIGIT111;
}

Once you have the circuit working, try it for real! Turn in your code and a completed schematic. Also, comment on what code and hardware alterations would be needed (if any) if common cathode displays were used instead of common anode.