Neck Deep And No Idea Where To Start

[Wraithshadow]

The title gives a pretty good idea of why I'm here, but allow me to provide some basic information so you can tell me I'm nuts.

I'm working on a project, which is best illustrated via this image:

http://img214.imageshack.us/img214/5518/isoviewxl0.jpg

I'm trying to get all of the buildings to light up, via LEDs. I'm figuring on running tunnels through the pink stuff (insulation foam) in order to reach a basement of sorts under each building. I can then easily wire the entire board and access each basement by making the buildings removable (which is part of the plan anyways). Power source is not part of the layout, so no worries there.

But this is where things get complicated. I'd like to set up each building so that they can connect or disconnect from the setup. I'd like to be able to swap out buildings with other things that don't light up, so I'm guessing a parallel circuit under each building would be a good idea.

However, this variable amount of LEDs is where I'm lost. There's other question marks on this whole matter, but that's it for right now. I'm trying to figure out how to configure the setup so that I can run it with just one LED in the circuit, or 9 LEDs in the circuit. My understanding is that as I add and subtract LEDs from the circuit, the numbers change. So the table with 9 parallel circuits connected will have a lower current through each than the table with 1 parallel circuit connected. Which means I'd need different resistors to maintain the amperage at a level that won't kill the LEDs.

I have no idea how to do that. Or if I can do that, without having to get into a really complex setup. I'd like to do this very simply, so that I can just plug in a building and go.

I could also wire each building separately, I think, using watch batteries and the like, but that raises questions as well. Let's say I'm wanting to run things at 30 miliAmps, and the battery's rated for 120 mAh (meaning it'll provide 1 hour's worth of power at 120 mA), does that mean that at 30 mA it'll run for 4 hours? For 12 hours (4x as long for 1/4 power)? For more?

I've asked elsewhere and gotten conflicting advice, and after a lot of reading online I've got what feels like a very basic understanding of electric circuits, but nothing's really clicking and saying, "This is how to do it."

So, I figured I'd ask you guys. If nothing else, it should be good for a laugh (for you).

[Chacal]

First of all, do not place pictures directly onto the forum. Do not use the "IMG" tag, but the "URL" tag instead. That's because John (OneZero) and Linda, who so generously let us use these here forums, have a bandwidth cap on the service. Each time someone load this thread, the image is added to that bandwidth. So, please, get the image hosted somewhere else (Photobucket, for example, or imageShack, or YahooPhotos...), then post a link (using the URL tag) to the image's location.

Second, about the lighting question itself, we'll gat back to you in a minute.

[jwrjr]

Your understanding of 'mah' ratings is essentially correct, but there is a gotcha. The mah rating assumes a 'standard' discharge rate, generally C/20. Check the battery data sheet for specifics. Based on that, those 120 mah batteries assume discharging at 6 ma for 20 hours. If you discharge faster, then the rating goes down. (And yes, if you discharge slower, the rating goes up.)
For a project like that, I would use an AC adapter rather than batteries if at all possible. Barring that, I would use the highest current batteries that I had room for.
As for your other problem, run the power supply lines to each building. That way you can add as many led+resistor pairs as the power supply will support.

[Sparky]

As mentioned if each house has its own Resistor you can turn them on and off without impacting the other LEDs, this way separate resistors are a good idea, if one LED dies it won't cause the other LEDs to be stressed by the change in power.

One common buss power to every place you need power, than install the resistors and LEDs as need be. If you add something different to one spot and need the full power supply voltage you just tap the feed before the LED/resistor pair.