[sdiy] KN-75 optocoupler

[Tom Wiltshire]

On 21 Dec 2007, at 12:47, Paul Perry wrote:

> If it is a LED/LDR opto, and you have 'tested' it by connecting a  
> 9v battery
> directly across the diode, then it is now just a LDR, the LED will  
> have been
> destroyed (no current limiting resistor).

Strictly this is true, and it isn't a good idea, but in practice  
you'll mostly get away with it.
I've tested loads of LEDs by giving them a quick flash on a 9V  
battery, and it doesn't kill them. Mostly 9V batteries aren't a full  
9V either, unless you just got a fresh one for the test. Pull one out  
of a flanger pedal instead!
However, leaving them running like that would certainly be fatal.

T.