Looks quite useful. I wonder if the danger is really that great.
There you have it.
Someone who does not understand the danger thinks it "looks quite useful".
110v isn't quite as lethal as the 240v single phase mains (as used conventionally in much of the world outside North America).
In the UK, pro building site power tools etc are actually stepped down to 110v to reduce the risk.
But even so, 110v is not 'playful' stuff.
And 240 volts is deadly serious.
Good design keeps people and control logic well isolated from power.
This shield concept flies directly in the face of that.
As the original poster put it: -
I understand what you mean about doing a seperate box, however then there is no point of a shield at all, the only actual logic on the board is the arduino pins to drive the opto-couplers
So the only point of doing this as a shield is to deliberately bring power and logic (and by implication power and people) closer together. :-?
Much much much better to parcel up ALL the mains stuff in its own box with a mains inlet and outlet(s), plus neat connectors to take logic-level control inputs. And inside the box, on their way direct to the opto-isolators, keep those logic-level conductors physically isolated from the mains electric stuff.
A 'mains is live' neon indicator on the box would be good, too. And an isolation switch certainly wouldn't be a bad idea.
Then you have made yourself a general-purpose mains-controlling box for your projects.
With minimal risk of qualifying for an internet Darwin Award.
However if you were being sensible about it, you'd just buy SSRs to go inside the box, rather than building your own.
They are actually pretty cheap on eBay.
Well, I reckon as little as US $8 including delivery is pretty cheap for a nominal 25 amp unit ... (I went $10 for the Fotek one) ... the heat sink is actually more expensive than the SSR - but for switching only a few amps the heat sink isn't needed.
And for the truly prudent, its worth pointing out that you'd be even safer if you supplied the mains power to your project through an RCD (sometimes called ELCB) safety breaker plug.
Here's one UK example from B&Q http://nextday.diy.com/app/jsp/product/productPage.jsp?productId=16930
You'd probably never notice such a device, until it saves your life.
PS - People who write
I've been looking at doing some lighting control myself and have been researching building something like this.
...
I agree an SSR would be ideal, except in this particular instance I'd like the ability to dim lighting.
do not inspire me with confidence in their research!
I'd strongly advise such people NOT to "build something like this".
Especially when an SSR should be ideal for dimming lighting.
This thing is basically a homebrew quad SSR, but 100% exposed and bringing mains electricity intimately close to the Arduino (and anyone 'interacting' with the Arduino).