Opto Coupler Common Ground

[xenobie]

Hi Guys,

As I understand opto couplers, their main use is to isolate a circuit from another,mainly for protection purposes. In my case I have an Arduino which controls a couple of shift registers (74HC595) which trigger transistors and I would like to protect the Arduino and the Shift Registers from any damage.

Since the Arduino works with 5V, and the Transistors will be switching 12 - 14VDC, BOTH INPUT and OUTPUT will be using the same ground. My question is this. Does it make sense to use an opto coupler since I will be using the same Ground? I mean is there any protection at all?

Some more info on the power source:
The main power source is going to be a car battery OR an ac transformer converted to DC. For the Arduino I am going to get this voltage and stabilise it using a 7805.


Thanks a lot 

[Hero999]

There is no point in using an opto-coupler, if both circuits use the same ground.

[xenobie]

That's what I thought.. so is there any other way to protect your circuitry apart from using opto couplers and  2 different supplies? I must use only 1 car battery.

Thanks for your reply too
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