Solved - Question about 3v3 to 3v3 isolated switch (opto coupler)

Projects General Guidance
1

Hello,

I have tried to search and find a solution to my hobby project. I think I have found a working soluton, but would highly appreciate a second thought.

I want to control a button both by pressing it and activating it with my Raspberry/Arduino GPIO. The coupling needs to be opto isolated.

Image1 shows the circuit I want to extend. Image 2 shows my proposed solution.

Would be happy for any comments. And I also need advice on which optomos/photomos to buy for this purpose. I need both Normally Closed and Normally Open versions of the component.

Edit: For now I just need advice for a suitable NO Optocoupler

-Are

image001.jpg
image001.jpg851×617 7.45 KB

image002.jpg
image002.jpg1156×576 15.7 KB

2

Optocouplers are usually Normally Open. Explain why You want Normally Closed?

3

You are right. I will probably only need NO Optocouplers. But in my project (read: in my noob brain) I think maybe there will be use of a NC solution if there is a situation where interrupting the current triggers an event.

Thank you for addressing this. I will just need advice for a suitable NO Optocoupler for now :slight_smile:

4

Just search on Internet. Ebay surely have such devices, Amazon...… If You have more local suppliers, check them up.

5

Using low voltage and low current almost everything will work.

6

Oh, believe me, I have :smiley:

https://www.elfadistrelec.no/en/optoelectronics/opto-photo-couplers/c/cat-L3D_525323

I don't even know which category to start looking in :frowning: sorry.

7

Are You Swedish?
The Transistor Output Optocouplers ought to work. There is a category of High Speed/Logic Optocouplers in case of high speed.
In Göteborg there is a guy, Tema Elekronik, adress Nordostpassgen, that is selling components like that.
I've used some old Sharp PC815.

8

Close, neighbour :slight_smile:

Didn't find the Sharp, but I think EL817 looks promising ?
https://www.elfadistrelec.no/en/optocoupler-dil-35-everlight-electronics-el-817/p/17539000?q=&pos=1&origPos=1&origPageSize=10&track=true

Regarding speed I think 4 µs is fast enough for me. But thank you for pointing that out :slight_smile:

9

I couldn't any respose time, Your 4 Micros. Where is there "a 4 mikro second"?

That device is likely good for You. Buy a few!

10

I was thinking about the rise and fall time ? But that might be the wrong "timer" .. I noticed the rise and fall was significally lower on the high speed ones.

Thank you very much for the help, Railroader. Karma given :slight_smile:

11

Thanks! Good luck finishing Your proj.

12

If you are putting your circuit in parallel with a physical button, transition time is not really relevant. How fast do you think a human pushes a button? Do you really plan on "pushing" this button thousands/millions of times a second?

13

Very good point, blh64 :slight_smile: