parallel port light detector

I connected a 3v source with a 680ohm resistor to pins 1 and 2 of the opto coupler. Pin 12 stays low, it does not fluctuate. The opto coupler works fine with 4mA.

I = V/R
I = 3/680
I = 0.004A

I think the problem is the fluctuating voltage on pin 1 and pin 2. As the voltage rises from 1.06v to 1.19v that must be causing the photo transistor to turn on and off.

I am thinking I need a voltage regulator.

Vout: Led(2.1v) + LTV-814(1.2v) = 3.3v
Vsource: 43v
Imax: Led + LTV-814 = 10mA + 1(10% safety buffer) = 11mA

http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm

3dOptics said:

The opto coupler works fine with 4mA.

Click to expand...

The voltage from the motor feed must be fluctuating a lot then. How fast does the opto need to turn off in response to the motor turning off?

kchriste said:

How fast does the opto need to turn off in response to the motor turning off?

Click to expand...

Response time is not critical.

There are a few ways to do it.
Take care of it in software. ie: write a "debounce" routine.
Or add a bridge rectifier, another resistor, and polarized capacitor.