[sdiy] KN-75 optocoupler

[anthony]

Nonono, I have a 9V battery pulg with a resistor, and incandesant  bulb and 
some aligator clips on it. One way I use it is as a continuity detector; 
this uses a clip that bypasses the resistor and lights the bulb; another 
clip bypasses the bulb and has the resistor in series with the battery to 
test LED's. Usually it's to search for my random salvaged, blue LED's, 
because they're water clear like any other color. Blue LED's can take a full 
9V battery hit and live for a while though. So can "white" LED's.

I figured it'd be more expedient to just say I connected the battery to it 
to save words. But even if I HAD toasted the LED, I still would have gotten 
a drop in the resistance in the LDR on the other side - if only for  moment, 
but I didn't.

I've seen Neon bulbs used as discharge gaps too, but I have a hunch that 
this thing is the ring detector: the ring signal is a 90VAC burst, which is 
more than enough to get a neon bulb going. The drop in resistance will let 
the machine know that a call is coming in.

> 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).
>
> In Finnish, the KN-75 is called an "opto-putki" which I think is "light
> pipe" or "light tube" FWIW.
>
> As for neons in answering machines, I've seen them as static electricity
> discharge gaps.
>
> Paul Perry Melbourne Australia
>
>
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