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Topic: Questions about Optocouplers (Read 554 times) previous topic - next topic


So Ive got a 40amp 600v Triac coming and want to control the speed of an AC motor with Arduino, The motor is a universal motor and It has some kind of hall sensor.

I have looked at simple designs such as;




The first one uses a MOC3041, and the other one also uses similar optocoupler.

But I don't understand how these optocouplers work, do They send and recieve signals to the Arduino or do they just Trigger the Triac every zero crossing time and take input from the arduino?

What are the advantages of using a Zero-crossing Optocouple as oppsed to a random phase optocoupler?

My ultimate goal is to have a potentiometer to adjust the speed of the motor, have the Arduino take input from the hall sensor and adjust the Triac triggering for stable RPM, I would also like the RPM to be displayed on an LCD screen.

The motor is quite fast for my application so I'd like to be able to control the lower speed range and sacrafice the top end, but it seems many commercial Triac circuits have limitations at the lower end so they may only control the speed from 10-100%, This is not ideal for me.

Anyway any insight on the optocoupler would be great.


Hi there,

opto-couplers are there to electrically isolate 2 circuits.

Well, you better read up a bit on them here :


and here :


I'm no expert, but they are very simple to understand.

Good luck,

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