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I want to switch on/off some AC device using solid state Omron G3MB relay I know that for magnetic relay there should be transistor and flyback diode, but what about SSR? Can I connect it directly to arduino digital pin without any transistors and anything else?

In a closer look on special arduino module, we can see some extras. Are they necessary? I want to put solid state relay (not separated module) into my custom PCB, and I'm confused about that extras.

Arduino module

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  • yes, that's the idea; it's just a resistor and an LED as far as Arduino sees.
    – dandavis
    Nov 23 '20 at 20:18
  • Mate, according to the datasheet you provided it's safe to hook the arduino, but to be safe put a resistor in between, just to be sure the SS relay don't pull up to much current from the Arduino, as this may casue harm to your device.
    – k.Cyborg
    Nov 24 '20 at 4:49
  • @k.Cyborg am I misreading the datasheet? The way I read it, there are multiple (sub-) models of the G3MB. Some of which don't require a resistor, but some do.
    – Gerben
    Nov 24 '20 at 14:55
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According to the datasheet there are multiple models.

Some already have an input resistor for the led (in the opto-isolator) inside the package, but some don't. For the ones that don't have a resistor inside, you'd need to add one yourself, to limit the current to around 10mA.

Some models also have a snubber circuit inside the package. The need for this depends on what kind of load is connected (inductive vs. resistive (AFAIK)).

I thinks the green thing, in the picture, is a fuse. On the other side of the SSR you can see and indicator led, transistor, and 3 resistor (one to limit current to the SSR, one to limit the current through the indicator led, and on for the base of the transistor.). They probably use a transistor, because the current for the SSR and the indicator led combined, is to high for certain micro controllers.

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  • the transistor is likely used as a current limiter for the ssr's led, just like commercial fotek et al.
    – dandavis
    Nov 24 '20 at 20:06
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The answer is a qualified yes. In this case the relay is optically isolated from the load so there is no cross conduction. You need to connect the relay to the Arduino power +5 and Ground supply. I would not connect more then one to any arduino pin as the relay has a max requirement of 20mA. Not all SS relays are the same so you need to check there specs if you use another one.

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