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 Post subject: Interface to an existing LED circuit
PostPosted: Wed Apr 23, 2014 3:44 am 

Joined: Sat Apr 19, 2014 5:19 pm
Posts: 1
Often time there is a working piece of equipment with LED annunciation that you wish you could "bridge" in some fashion to connect to other equipment and know if the LED is on or off.

How would one electrically (not optically) "bridge" such an LED such that you can trigger a logic input on some other piece of equipment and stay isolated between the 2. I wish that there was a simple device that you could simply attach to the legs of the LED and get a near short on another set of legs. Ideally there are no external power supplies involved. Is there perhaps a very hi impedance Opto that could be used more or less generically on most any pre-existing LED circuit?

Maybe the brain trust has the answer or a suggestion on how to Google the question.

Thanks in Advance


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 Post subject: Re: Interface to an existing LED circuit
PostPosted: Wed Apr 23, 2014 11:17 am 
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Joined: Fri Feb 08, 2002 1:01 am
Posts: 4284
Location: USA / North Carolina / Fayetteville
put a opto-isolator in series with the led..not parallel ( won't work )
then on the other side of the opto- put your circuit to use what ever it is...
you may, or may not have to adjust the series resistor of the led.
i have seen many circuits have a led in series with the opto-isolator and they work just fine


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 Post subject: Re: Interface to an existing LED circuit
PostPosted: Sun Apr 27, 2014 6:56 am 
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Joined: Thu Oct 26, 2006 7:11 pm
Posts: 1316
Location: Maryland
Yup
That is the way to go. Safe isolation low cost and an easy to-do.
Isolator could be in or out of the equipment. Isolators are available with parallel opposing dual LEDs so polarity is not important. Transistor, triac or resistance outputs are all common. Multiple isolators in the same package can also make it simpler.
Len



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Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)
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