Living Architecture Fall 2009 Pratt

//
// This example shows one way of using an LED as a light sensor.
// You will need to wire up your components as such:
//
//           + digital2
//           |
//           < //           > 100 ohm resistor
//           < //           | //           | //         -----
//          / \  LED, maybe a 5mm, clear plastic is good //         -----
//           | //           | //           + digital3 //
// What we are going to do is apply a positive voltage at digital2 and
// a low voltage at digital3. This is backwards for the LED, current will
// not flow and light will not come out, but we will charge up the
// capacitance of the LED junction and the Arduino pin. //
// Then we are going to disconnect the output drivers from digital2 and
// count how long it takes the stored charge to bleed off through the
// the LED. The brighter the light, the faster it will bleed away to
// digital3. //
// Then just to be perverse we will display the brightness back on the
// same LED by turning it on for a millisecond. This happens more often
// with brighter lighting, so the LED is dim in a dim room and brighter
// in a bright room. Quite nice. //
// (Though a nice idea, this implementation is flawed because the refresh
// rate gets too long in the dark and it flickers disturbingly.)
// #define LED_N_SIDE 2 #define LED_P_SIDE 3  void setup() {}  void loop() {  unsigned int j;  
// Apply reverse voltage, charge up the pin and led capacitance 


pinMode(LED_N_SIDE,OUTPUT);
pinMode(LED_P_SIDE,OUTPUT);
digitalWrite(LED_N_SIDE,HIGH);
digitalWrite(LED_P_SIDE,LOW);

// Isolate the pin 2 end of the diode

pinMode(LED_N_SIDE,INPUT);
digitalWrite(LED_N_SIDE,LOW);

// turn off internal pull-up resistor  
// Count how long it takes the diode to bleed back down to a logic zero  for ( j = 0; j <>

SOURCE:

http://www.arduino.cc/playground/Learning/LEDSensor

Labels: K.A.A.S., Living Architecture, Pratt, Responsive Architecture

# posted by Anka : 2:19 PM