It should be ground.

And if Vdd is 12V then the control voltage must also be 12V, not 5V.

Thanks.
I'll use Digital Logic Level Conversion for my Arduino.

 

How much current are you hoping to pass through the IC? Each channel is rated for 10mA max.

 

How much current are you hoping to pass through the IC? Each channel is rated for 10mA max.

74HC4066 could provides more current.

 

How much current are you hoping to pass through the IC? Each channel is rated for 10mA max.

I didn't check it yet. I guess 10ma is OK.
but I used a PC817 tested works well.

I was thinking the Optocoupler components can't work same as the relay which is just mechanically contact. not clear whats the difference between them.

 

I didn't check it yet. I guess 10ma is OK.
but I used a PC817 tested works well.

I was thinking the Optocoupler components can't work same as the relay which is just mechanically contact. not clear whats the difference between them.

View attachment 261772

Optocoupler is used for high speed and lower current than a relay.

Edit: Mostly the relay is worked for less than 10 times(10 on/off) in 1 sec. (<10Hz)