Opto-isolation questions

Roger Pierson

Greetings friends and neighbors!

This will be my first direct experiance using opto-isolation, so I have a few questions.

First, if I use an ULN2803 darlington array to control a load, is it even necessary to optically isolate the Stamp? Does the ULN need protection in this manner?

Second, say I wanted to control some Solid State Relays directly from Stamp pins, what type of opto-isolator would be the best choice for this applicaton? Does the source current for the isolator come from the Stamp input or an external source?

I appreciate any advice!

Roger

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Roger Pierson
Senior Electronics Technicain
DTI Assoicates

bennettdan

I got a goot deal on 4n25 optoisolators but you might want a multichannel opto ...

Randy Evans

Roger:

First, no. If the load needs isolation, then use an opto-isolator instead of the ULN2803. There's usually no reason to do this.
Second, definitely no. An SSR is an opto-isolator.

Randy

Roger Pierson

That makes sense. The Crydom SSR's I want to use draw 10ma according to the datasheet. If the BS2 can source up to 40ma per 8 pins does that mean I can safely run 6 SSR (60ma) as long as I divide the outuputs up between P0-P7 and P8-P15?

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Roger Pierson
Senior Electronics Technicain
DTI Assoicates

Bill Chennault

Roger--

Take a look at this thread wherein you will see that I had the almost identical thinking. You will also see how that thinking evolved, which might be instructive.

http://forums.parallax.com/showthread.php?p=609026

Merry Christmas!
--Bill



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You are what you write.

Roger Pierson

Thanks for the help, guys. Bill, that's a great thread!

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Roger Pierson
Senior Electronics Technicain
DTI Assoicates