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Opto Isolator? Answered

From everything i have read it looks to me like you can use an opto isolator with different output voltage as compared to the input voltage. 5 Vdc input side and 12 Vdc output side. Is this correct or have i got this all wrong? 

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icengBest Answer (author)2012-04-11

Yes, in fact the separation voltage could be a couple of hundred volts.

This feature allows medical devices to be approved to measure human
bodily functions or operation of factory sensors across transformer phases.

P.S.  Most optolators are NPN output transistors your sketch is a PNP.

a

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WWC (author)iceng2012-04-12

Thanks i was looking for a conformation on what i had already learned. Double checking i guess you call it.

I don't know whos sketch this is i only pulled from the internet, mainly because it shows 2 batteries, one for each side.

Every place close to me is out of 6v relays so i am planing on switching to 12v relays and using this opto to do it..

I give you best answer. Almost to the century mark huh? Wayne

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iceng (author)2012-04-12
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WWC (author)iceng2012-04-12

Here's my hillbilly sketch. Suggestions?

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iceng (author)WWC2012-04-12

Cant make out the text and barely the wiring ?

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iceng (author)2012-04-12

Thank you here are some opto isos.

The current capability of single npn optos may not be enough
for a relay you are far from parts stores in Manila Ill add one
more ckt in a few min.

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pfred2 (author)iceng2012-04-12

The current capability of parallel ports isn't exactly unlimited either. While many can drive the LED in an optocoupler not all can. Some parallel ports cannot source or sink more than three mill-amperes, which is not enough to reliably switch on many if not all optocouplers. Personally I wouldn't and don't just use parallel port without buffers to drive any loads. I've even posted an article on this site addressing the issue. What I do has the distinct advantage of working no matter what its other flaws may be.

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WWC (author)pfred22012-04-12

It will work no mater what it other flaws may be, because it steps up a week high logic signal to 5..0v and to 24 mill-amperes?

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WWC (author)iceng2012-04-12

Yes Thanks. I am using the opto for the isolation from my LPT and voltage difference for the relay. I am using BC547, resistor and diode ect for the relay coil circuit.

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steveastrouk (author)2012-04-12

Strictly speaking, here you don't HAVE to use an opto. They're great, because they allow you to completely break earth loops and avoid noise issues - as well as allow you up to 4000V from one side to the other !

But to switch a 12V relay, just use a transistor (and a flywheel diode)

Steve

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WWC (author)steveastrouk2012-04-12

I am triggering from my parallel port of my computer so i also wanted isolation for that.

I may use all of the 8 ports eventually from the LPT. Each relay has its own little board with a 4 pin opto also, located in different arts of the house.

I will run 18v and a logic line to each board. Then regulate voltage with a 7812.

Dont know if that's the professional way to do it, buts that's what my hillbilly engendering came up with.

I will have to research ( flywheel diode ). Thats a new one for me.

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steveastrouk (author)WWC2012-04-12

Ah, in that case opto isolation is the way to go

FYI, the IN4001 diode in the https://www.instructables.com/files/deriv/FB9/RI48/H0OJ01Y5/FB9RI48H0OJ01Y5.MEDIUM.jpg are called "flywheel" diodes.

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pfred2 (author)steveastrouk2012-04-12

I've heard of freewheeling, or flyback diodes in connection with inductive loads. I guess a flywheel diode is somewhere between the two :)

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WWC (author)steveastrouk2012-04-12

Ah yes i use them that way, I just didn't know that's what they were called.

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