What is optoisolator?

Thread Starter


Joined Dec 9, 2011
Hi someone can explain me about optoisolator?
In the last week, I went to electronic shop to buy relay for switching AC light bulb from Arduino. The shopkeeper said, they don't left any relay. At that time, other buyer said, why don't you use optoisolator and give "MOC3023 and BTA08-600C" to that boy. So I request to that man, Can you explain me how to use it. But he said, sorry son, I have to go now and you can use that two instance of relay. Then shopkeeper give me that two.

Can someone explain me how to drive that two from Arduino or any microcontroller for switching AC load.:D


Joined Apr 5, 2008

A relays is an electro-mechanical device.
It contains a coil and a set of mechanical contacts.

An optoisolator is a combination of a led with an other active element inside.
The active element can be a transistor, in case of an optocoupler
or a triac in case of an MOC device.

There are several types of these MOC devices.
There are zero-crossing devices, that will switch on the next zero-crossing of the sinewave
and non zero-crossing devices, these will switch immediately and can be used for dimmer circuits.



Joined May 11, 2009
I guess you will have a go on the problem by your self first. Take a look at the datasheets. You will find some applications that will help you
But I will say that it is some safety aspect about this setup. That I do not feel quite comfortable with. For a beginner to work with. This is not an application you should leave in unattended operation. Check the temperature on the BTA08-600C. It will probably need to be mounted on some cooling finn


Joined Apr 27, 2007
The MOC3020 contains a phototriac (represented as a diac). It is used to trigger the BTA08-600C, which is a triac.

Personally, I would prefer to use a bi-directional solid state relay, as it is an industry standard. Bi-directional solid state relays work like optocouplers, but they have two MOSFETs in series, in opposite directions. They work very well and they are less complicated.


Joined Nov 8, 2011
In terms of name. Optoisolator/optocoupler is a device which consists of a photo emitter diode which like a LED on one side and a photo sensitive transistor on another receiving side. It is mainly used to isolate two different parts of circuit like high and low voltage parts, high current or noise and dedicated digital parts. What you got to buy is a opotoisolator Triac driver output, it's construction is similar as the first one but it includes Triac on the receiver side instead. So, it has both the isolation and power adjustment function (by the Triac) in a chip. For how to control power by Triac, you got to read some topic of Triac...