//
// Light level detector demonstration.
//
// Pin P1_4 is connected to one side of a cadmium sulfide photodetector.
// Pin P1_5 is connected to the other side of the photodetector.
//
// There is a 1k ohm resistor between P1_5 and ground to form a voltage divider
// with the photodetector.
//
// The low four pins of Port 1 are connected to LEDs whose other side is grounded
// The low six pins of Port 2 are connected to LEDs the same way.
// There are ten LEDs in a row, showing us the ten bit output of the analog
// to digital converter, which is reading the voltage on pin P1_4.
//
// That voltage is between zero and the 2.5 volt reference.
// There are 1,024 levels in ten bits, so each level is 2.4414065 millivolts.
//
void
setup( void )
{
  P1DIR = 0b1111;          // low four bits
  P2DIR = 0b111111;        // low six bits (makes 10 bits total)
  
  //
  // Set the reference to 2.5 volts vs ground, turn the reference on,
  // and make it available on pin P1_4 (the reference output pin).
  //
  analogReference( SREF1 | REFON | REFOUT | REF2_5V );
}

void
show_value( unsigned value )
{
  P1OUT = value & 0b1111;
  P2OUT = (value >> 4) & 0b111111;
}

void
loop( void )
{
  show_value( analogRead( A5 ) );
  delay( 100 );
}