Proxy-switch, bi-dir LED

Hello all!

Just did my first little project with my new Arduino. All my electronics stuff is stored away after I moved this summer, so all I had to play with were some LEDs. So, I made a proximity-toggleswitch using a LED as a sensor. Pretty simple, one LED is connected between digital out 2 and 3 (long leg on 2), and another between 13 and ground for indication. When the switch is toggled on or off the Arduino sends a 1 or 0 (respectively) to my computer running a botched-up 2 minute Visual Basic program.

/* LED sensor -- photodiode.

int anodePin = 2;
int cathodePin = 3;
int value;
int prev;
unsigned long lastupdate = millis();

void setup()

  //deactivates pullup resistors?
  _SFR_IO8(0x35) |= 4;
  _SFR_IO8(0x35) |= (1<<4); 

  pinMode(anodePin, OUTPUT);      // sets the digital pin as output
  pinMode(cathodePin, OUTPUT);      // sets the digital pin as output

void loop()
  //emit light
  digitalWrite(anodePin, HIGH);
  digitalWrite(cathodePin, LOW);
  //switch potentials -- charge LED to -5V
  digitalWrite(anodePin, LOW);
  digitalWrite(cathodePin, HIGH);
  //measure time for potential to equalize (for cathode to be LOW)
  //switch pinmode 
  pinMode(cathodePin, INPUT);
  //measure time it takes for cathodePin to go to zero
  //this value probably depends on the chip clock or something
  value = 0;
  while(digitalRead(cathodePin) != 0)
  //check if the change in measured value is greater than a certain threshold, and if the last update was more than a second ago
  if((prev - value < -1000 || prev - value > 1000) && millis()  > lastupdate + 1000)
    lastupdate = millis();
    if(digitalRead(13) == LOW)
      digitalWrite(13, HIGH);
      Serial.print(1, DEC);
      digitalWrite(13, LOW);
      Serial.print(0, DEC);
  prev = value;
  //illuminate led
  pinMode(cathodePin, OUTPUT);
  digitalWrite(anodePin, HIGH);
  digitalWrite(cathodePin, LOW);

I know it ain’t much to brag about, but it’s kinda cool as the program sort’a autocalibrates, so it will work reliably both in light and dark conditions. :smiley: