Virtual switch

So instead of http://www.allelectronics.com/make-a-store/item/RLY-648/5-VDC-DIP-RELAY/1.html what relay do I get from all electronics?

The one that I linked to back in Reply #2 because it only needs 31ma to turn it on, which the Arduino can handle.

I don't think any of these will work without a transistor as they all need too much current.

Maybe this one. How many volts across the 2 wires?

Even with the lower current relay you still need the diode or the reverse EMF can fry the arduino

I should have stated this in the beginning but the flash is a disposable camera flash and the idea is just to make a high speed photography trigger with the parts available at www.allelectronics.com. What parts would I need? I was thinking of using this: Arduino High Speed Photography Trigger - YouTube
but I cant find a Opto Isolator at All Electronics that works.

MOC3020

I cant seem to find that at the Allelectronics website.

I know how to use google. I want to get the optoisolator from All Electronics as it is 5 minutes from where I live.

Maybe they don't stock such useful items, and you'd have to spread your seach a little wider.

What are the specs that I need on the optoisolator for this to work. I will go to all electronics today and compare the selection to the specs and buy a few. All Electronics has the following on there website:

NPN transistor output. 6 pin DIP package.
NPN darlington output. 6 pin DIP package.
Would any of these work?

When I went there previously they had a few more in store than they had online.

Opto triac, or opto-transistor plus external triac or thyristor.
An optotransistor by itself isn't going to work at flash trigger voltages.

By searching that I found a Triac-output, 400V optoisolator. 6-pin DIP package at allelectronics: http://www.allelectronics.com/make-a-store/item/MOC3022/OPTO-ISOLATOR-TRIAC-OUTPUT/1.html

That will work right?

Datasheet here: MOC3022 Datasheet(PDF) - Texas Instruments

A MOC3022?
Yes, I think that's close enough to a MOC3020.
There's a very subtle difference, can't remember what is is - maybe the datasheet will make it clear.

I will get it. When I do get it though is there a chance that I could fry my arduino?

Not if you wire it up right.
I use MOC3020s to fire 20-odd year old flashguns, plus some home-brew devices.
One commercial unit has a voltage of around 180V across the terminals.
Another, with the same model number, but about 5 years younger, has about 6V.
Just make sure that all the output terminals of the isolator are connected to is the flash.
Nothing common, hot-side.

Thanks! I will post back here if I run into any problems.

Don't forget to add a current-limiting resistor to the input side.

Got it, Thanks again!