How do I provide a finished project with a 5v power supply?
I need something like this which I can plug a 5v adaptor in to then use to power other components, but this is obviously built for a breadboard and there's no obvious way to mount it inside a plastic box?
I need this for a relay -- it requires two 5v power supplies, one from the arduino (via breadboard jumper cables) and another to keep it opto-isolated.
If you use something like that and two wall-wart power supplies, you'll have isolation. So, why not just use a 5V wall-wart? (If you use the same main power supply for both circuits, you are not isolated.) You could also use an isolated DC-DC converter module.
Are you sure you need opto-isolation? A relay is already isolated (there is no electrical connection between the coil and the contacts).
but this is obviously built for a breadboard and there's no obvious way to mount it inside a plastic box?
I see pins on the bottom, like it's designed to be plugged-into something.
Some pre-built relay modules for the Arduino include an opto-isolator. There is no reason why you can't use the same 5V for both the Arduino and the relay board's power. As already mentioned, the relay provides galvanic isolation from the controlled circuit.
If you have an aversion to using an external regulated 5V wall wart (say you want an internal transformer) a good high efficiency module to use is called a UBEC - Universal Battery Elimination Circuit. This is like that 5V linear regulator board in your post, but typically uses a switching regulator instead which is much more efficient and generates considerably less heat. One I use lots of are: Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking
Anything that can be plugged into a breadboard can be attached to prototyping boards as well is you want to make it more permanent.
Thanks the replies. In the end I bought these 5v DC power supply sockets: http://www.ebay.co.uk/itm/181143306558?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2648
I've read it's better to avoid having both low and high voltage in a single box, but in this case I'm not sure how to avoid that. The relay box will have a 5v AC->DC adaptor plugged in to it as well as the AC mains. Seem ok?
I want opto-isolation because the arduino will probably be plugged in to my PC via USB when I'm prototyping.