simple 2-digit display that shows the current light level in values ranging from 00 to FF

light_dependent_display.ino

#define CLOCK_PIN 2
#define LATCH_PIN 3
#define DATA_PIN 4
#define READ_PIN 0
#define OPEN_LATCH digitalWrite(LATCH_PIN, 0)
#define CLOSE_LATCH digitalWrite(LATCH_PIN, 1)

byte digits[16];

void setup() {
  pinMode(LATCH_PIN, OUTPUT);
  pinMode(READ_PIN, INPUT);
  digits[0x0] = B00111111; // read right-to-left, not left-to-right
  digits[0x1] = B00000110; 
  digits[0x2] = B01011011; 
  digits[0x3] = B01001111; 
  digits[0x4] = B01100110; 
  digits[0x5] = B01101101; 
  digits[0x6] = B01111101; 
  digits[0x7] = B00000111; 
  digits[0x8] = B01111111; 
  digits[0x9] = B01101111; 
  digits[0xA] = B01110111; 
  digits[0xB] = B01111100; 
  digits[0xC] = B00111001; 
  digits[0xD] = B01011110; 
  digits[0xE] = B01111001; 
  digits[0xF] = B01110001; 
}

void loop() {
    int reading = analogRead(READ_PIN);
    int brightness = map(reading, 0, 0x3FF, 0, 0xFF);
    int firstDigit  = brightness / 0x10;
    int secondDigit = brightness % 0x10;
    
    OPEN_LATCH;
    shiftOut(8, digits[secondDigit], DATA_PIN, CLOCK_PIN);
    shiftOut(8, digits[firstDigit],  DATA_PIN, CLOCK_PIN);
    CLOSE_LATCH;
    
    delay(100);
}
// the "bits" parameter was added for easy expandability; 
// but I haven't made anything yet that fully utilises it
// so it's sorta just there as a leftover that I'm too lazy to edit
void shiftOut(int bits, byte input, int dataPin, int clockPin) {
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);
  int pinState;
  
  digitalWrite(clockPin, 0);
  digitalWrite(dataPin, 0);
  
  for(int i = bits -1; i >= 0; i--) {
    digitalWrite(clockPin, 0);
    
    if(input & (1 << i)) 
      pinState = 1;
    else 
      pinState = 0;
      
    digitalWrite(dataPin, pinState);
    digitalWrite(clockPin, 1);
    digitalWrite(dataPin, 0);
  }
  
  digitalWrite(clockPin, 0);
}