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Do all opto couplers invert the output?

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I wanted to buffer the output pin of an ATMega 328 chip that feeds a transistor switch controlling a big relay. I was thinking of using an opto coupler to isolate the ATMega, but the ones I have looked at invert the input, which I don't want. Do some not invert it? Thanks
 

Reloadron

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Not quite getting what you are saying as your code will determine what an output pin does for any given condition. That said this would be better answered if you provide a drawing and explain in detail exactly what you are trying to do. Links to data sheets would also help with "big transistor" and "big relay". Anyway your code will control the output logic state.

Ron
 

canadaelk

Active Member
How big is big (as in big relay)?
Many opto-couplers do not care if you put the load onto the high side (Inverting?) or low side (non-inverting?) of the output. But why use an opto-coupler when you already have a driver transistor there? E
 

Reloadron

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Most Helpful Member
But why use an opto-coupler when you already have a driver transistor there?
A problem frequently encountered, even when using a good decoupling capacitor on the uC (ATMega 328 chip in this case) is getting the uC and relay to share the same power supply. This is true even when we use a flyback diode on the relay coil. Frequently an opto-coupler is used to solve the problem. This affords isolation between the supplies. That said it just is, as you mentioned, a matter of configuration.

Ron
 

MaxHeadRoom78

Well-Known Member
As mentioned, just use the emitter output instead of the collector .
Or use a Mosfet to drive a relay , 2n7000 and up, and use NC or NO contact for inversion.
Max.
 

alec_t

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Most Helpful Member
Inversion or not can depend on whether the micro drives the anode or the cathode of the opto-LED.
 
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