How hard is it to build a toy control panel?

I made this sort of stuff myself when I was 10, running wires from 9V batteries through switches and light bulbs and potentiometers and never once set myself on fire. There is only so much energy in a 9V battery. Just don't build one that runs on 110V AC and you can't screw up that badly.

Cool idea. Running off a batteries should be fine, the current will be too low to cause problems. But I would be worried about small electrical components getting chewed on and swallowed. In particular I would keep the 2YO away from anything soldered.

Your only risk of danger is if you accidentally wire a battery to short and then leave it on for long enough for the battery to rupture or the heat in the wires to burn wood or paper. If you use a battery case instead of tape and raw batteries (ala my early experiments with electronics at 9/10), you'll be less likely to do that. Your best friend is good layout, and an understanding of series vs. parallel. You'll probably also need to understand resistors - color codes, and what values are required for the lit elements you're going to use (LEDs, I'm assuming). The risk is actually pretty small, and easy to test for. Build your circuit, turn it on for a bit, turn it off, feel for hot spots. Nothing warm? You're good to go.

You may not have to reinvent the control panel. Maybe http://www.smarthome.com/_/index.aspx could be cannibalized to make all kinds of magic happen:

If you just want switches and lights, it's easy to wire up, and hard to burn your house down if you don't use more than 4-6 batteries (I'd use D cells, especially if there are lots of incandescent bulbs in the panel). You can get (much!) better battery life at the cost of a modest increase in complexity by using LEDs instead of 6V light bulbs. There's plenty of information on the 'Net about simple LED lighting projects; the thing you'll want to Google for is "current-limiting resistor". If you're starting from scratch, look for a local electronics surplus store and go for a visit. You may find obsolete control panels for cheap, which will be full of switches and other mechanical doo dads that are shockingly expensive if you actually need a 3-throw, 8-pole rotary switch. The people there (at least if your surplus store is like mine) will know how to do what you're trying to do, and will be happy to give you pointers. If you want more complexity than just "this switch turns that light on and off," you can upgrade later by putting in a hobbyist microcontroller; Google for Arduino to get started.

Would buying a http://www.amazon.com/exec/obidos/ASIN/B0002AHQWS/metafilter-20/ref=nosim/ be cheating? It's sure a heck of a lot easier. I linked to the over the top kit we have but the same company makes a bunch of different sets priced from ~$20.

Use standard alkaline batteries, not rechargables. Rechargable batteries (pretty much any kind) can dump way more current into a short. Your wiring mistakes are far more likely to catch on fire when using rechargables.

You can always build it with a fuse. That's overkill on safety, but nothing wrong with it if it gives you piece of mind. You normally size the fuse to protect your wire, which depends on the wire diameter. You can find tables (probably on Wikipedia) that will tell you what size fuse to use for a given wire size. On a different note, check out the websites that laser cut and etch plastic or wood. You could get a super-cool front panel made for cheap. Great project. Sparkfun.com is your friend.

spacewrenchhttp://ask.metafilter.com/227327/How-hard-is-it-to-build-a-toy-control-panel#3289480 "hard to burn your house down if you don't use more than 4-6 batteries (I'd use D cells, especially if there are lots of incandescent bulbs in the panel)." ryanrshttp://ask.metafilter.com/227327/How-hard-is-it-to-build-a-toy-control-panel#3289501 "Use standard alkaline batteries, not rechargables. Rechargable batteries (pretty much any kind) can dump way more current into a short." FWIW, a D-cell alkaline contains about 2x as much energy as a D-cell NiMH (~75000J vs ~40000J) and - while the internal impedance is considerably different (~200mΩ vs ~15mΩ) and hence the peak S/C current current varies (~7.5A vs ~100A) - both are capable of more than enough current into an accidental short-circuit to start a fire. In fact, due to the facts that 100A will quickly blow light wiring &/or melt soldered joints while 7.5A will heat similar wire to incandescent temperatures, and that a shorted D-sized alkaline can keep supplying that sort of current for longer than a typical NiMH or NiCd rechargable, then D-sized alkalines are actually more likely to "burn your house down" than NiMH. Not that I think that's a likely scenario, but better safe than sorry… Personally, in your situation I'd build and test it with alkaline AA's but leave room to fit a C or D sized battery holder to run it once you're finished. And maybe stick a 12V 10~15W lamp in series with the battery as a simple current limiter.