Help with a little project

[morkus64]

Hey all... As some of you know, I do theatrical set designs, and I've been looking into making tiny model stage lights to spruce up my models... I don't really know much about circuitry or anything like that, so if anyone could help me out on this, i'd be thrilled. I've drawn a little diagram for what i'm trying to do... If anyone can give me some ideas as to what specifically i should be looking for (especially with regard to led, resistor, battery and switch), how things need to be wired, or where to get various materials, or if anyone has any better ideas on how to do this, it would be much appreciated.

Image is here:
http://img42.imageshack.us/img42/9585/light7er.jpg

 

[morkus64]

oh, and for those confused about the gel bit... it's basically a thin colored sheet of plastic we use to color the light... not sure to what extent gel is used outside of the theatre

 

[Fullmetal Chocobo]

Alright. I've done so much stuff like this it is frightening... All for sh!ts and giggles too. Anyway. This page is awesome for calculating what size resistors you will need for LEDs. Basically, you find and get what LEDs you will need for what you are doing, and then you get the power supply and other stuff to match. After you get your LED, grab the right size resistor to wire it in with. Any switch can be used to do this, although one with two or three leads is going to be easier than those with 4+. My opinion though. As for battery, that depends upon what you are going for. Are you going to hook it up so that you can replace the battery? And what size (physical measurement) battery would work best? You can use anything from a small 9V battery to a big lantern 12V battery. Just be sure to change the voltage and the page above to what size battery you are loooking for. And because of the low power requirements, any insulated wire, about 22 gauge (18 - 24 would work I'm sure) would be fine. Let em know if you need specific items listed, and I'll hunt them down for ya.

 

[morkus64]

well, i don't want the whole thing to be more than 1/4" in diameter (and as short as possible... 1/2" is prefereable, but i imagine maybe not possible), so i was thinking one of those tiny lithium watch or hearing aid batteries... something tiny but reasonably cheap (no more than $2.50 or so)... I would like to replace the battery, definitly. I imagine that the battery will die long before the led, right?

Also, if the forward voltage of the led and the voltage of the battery are the same, is a resistor necessary? I know there are tiny 3V batteries, and i saw some 3V leds on ebay...

Thanks so much

 

[morkus64]

oh, also would i need any special material for the housing, or does the led not genereate enough heat to worry about it? I know they generate less heat, but would it be too much for, say... 1mm thick plastic tube?

 

[Lonyo]

Hmm, just read that in ambient temps of 60c or more, you need cooling. I'd assume from that the LED itself would never produce enough heat to hit 60c, and most plastics are fairly heat resistant, so I doubt it would be an issue.
I also have some bike lights made with LED's that are encased (in solid plastic) that dont really seem to heat up.

 

[Evadman]

Most LED's genenerate very little heat. It depends on the MCD. The higr, generally, the higer the heat output.

That design will need to be redesigned though. Your 'switch' is impossibly small, along with the battery. The mattery will be quite a bit bigger than the LED (expecially a 3mm). If yo are going or cheap, a 3v button cell would be the cheapest and most redily available, but they are roughly 10mm by 3-4mm thick.

The 'switch' could be as simple as a push lever behind the battery that moves the battery forward in the tube and breaks contact with one of the contacts on the LED. However, the contacts would have to be designed so that they had some give to make up for production size differences. You could not actually use just the leads fromt he :ED and expect them to last any appreciable amount of cycles with a switch, as they would fatigue nd snap. A spring steel woud be better.

I would think a better idea would be to remove the battery from the design. The tube would be the LED, resister and color filter. Then use a bus to move the power from a central power source (or a few power sources depending on the size of the set) to the LED clusters. That would give several advantages.

• The power source could be a LI/gellcell battery (rechargable, portable, cheap)
• You could toss relays into the circuit so the lights cold be controled from a central location.
• Power could come from a cheap wall wart
• You would not have to go flip 50 switches between scenes. Just flip a single relay
• tons of other stuff I didn't think of

The main disadvantage I can thin of is the routing of wire, which is probably why you had this idea in the first place.

If you want to go on the single self contained unit, check out some model railroad shops. There are already lights like these for railroad cars and buildings, but most are smaller than this and get power from a different source from a battery, though I have seen self contained ones.