Optoisolator NEC 2532 problem.

Discussion in 'The Projects Forum' started by SIcam, Sep 1, 2008.

  1. SIcam

    Thread Starter Active Member

    Aug 9, 2008
    I am having a problem with controlling a LED through an Optoisolator (NEC2532) from an arduino microcontroller.

    Problem: I expected the LED to be off until I trigger the Optoisolator similar to the following but trigger a LED instead of a Flash unit.
    Opto Spec Sheet: http://www.sparkfun.com/datasheets/Components/PS2532-Optoisolator.pdf

    Investigation: I have hooked a NEC2532 Optoisolator across the output on Arduino Output Pin 4 to Opto Pin 1 then from Opto Pin 2 to 50 Ohms resistance then to Ground on the Arduino Board. The opto is trying to control the on/off state of and LED. The LED is connected as follows: Arduino Pin 8 to 1k ohm resistor then to Pin 3 on the Opto then from Pin 4 on the Opto to a LED then from the LED back to ground on the board.

    I have Pin 4 (Control to the opto) set to LOW and Pin 8 (power for the LED) set to be ON 1/2 second then Off 1/2 Second. I expected the LED to remain off until I triggered Pin 4 to a logic HIGH state but the LED blinks like the Opto is not direct shorted from Pins 3 and 4 on the opto.

    Anyone got an Arduino that can tell me what I am doing wrong? Or does anyone know why the Optoisolator is letting pins 3 and 4 act shorted?
  2. bertus


    Apr 5, 2008

    I think you have the pins 3 and 4 the wrog way around.
    The diode in the optocoupler will conduct constantly , independend on the input.
    (this diode is there to protect against conntcting the wrong way around).

  3. SIcam

    Thread Starter Active Member

    Aug 9, 2008
    You are absolutely correct. I found this out about 2 hours after I posted the question. This is now working like charm. I know have the optocoupler connected to the output of the arduino with 50 ohms in series with it. I have a camera connected with 10k ohms resistors in series and it is controlling a camera. I now have time lapse photography.