IAN LANG ELECTRONICS
If you are doing anything at all with the Arduino UNO or Duemilanove then you will very soon hear the term "shield". A shield is a complete circuit that sits on a board (prototype or PCB) and has a series of male pins coming out of its underside that allow you to plug it directly into your Arduino board. The shield draws its power and all instructions from the Arduino and can't work alone.
There are literally hundreds of ready-made shields out there that allow you to do things like play wav files, run motors, run large loads and even one that turns your Arduino into a programmable games machine (it's called the Gameduino, if you're interested.)
You can of course make your own. You could use stripboard, or even matrix board, but I prefer the polished niceness of a ready made prototype board. Here's my useful little tool made on a protype shield board from Oomlout.
What it does is shows me the current state of any of the digital pins. It's useful for debugging when a complicated logic argument goes belly-up and I need to know what's happening where. If the pins don't light up as I predict, I know something in the code is astray and by seeing where it starts to go wrong I can focus my attentions on that bit of the sketch. The advantage is immediately obvious- I've got a circuit that I don't have to build every time and can just plug in and go with. It saves oodles of time.
You'll notice I double-stack my shield (that is I put an extra layer of header pins between shield and board). I like to put stuff under the shield too, but there isn't much room if you just use one set of headers, especially where the USB port is. It also means I can reach the reset button and don't need to add a new one on the shield itself.
I won't lie to you. Making these prototype shields is hard and you can expect your first two or three to be unmitigated disasters. This little thing in the video took four hours to plan, make and test. If you're not sure of your soldering I'd do a bit of practice first if I were you. When you are plugging them in to the board, make sure all the headers are aligned and in the holes before you push down and don't use a lot of force when doing so. This goes for all shields. No good will come of pulling and tugging, so treat them like eggs.
Shields are awkward and difficult to make, but the rewards they offer in saving time and releasing your board from a mess of wires is more than enough compensation.
Ian Lang, November 2011.