Hello, pardon me, I am uneducated and I did not know what site to post this on, this is what I stumbled upon. I am building a diorama and would like multiple colour lights throughout it and have no clue how to go about buying the hardware and installing it.

Fortunately my husband is the intelligent nerd that can figure this stuff out with just some quick information. We have no idea what to buy. I have a rough drawing of my idea. We just need to know what the items are called and how to install them.

Thank you for your patience and help, greatly appreciate it.

 

Let's talk power first- how long does this device need to run from the battery?

How much space (volume) is available for the battery?

 

Let's talk power first- how long does this device need to run from the battery?

How much space (volume) is available for the battery?

20 minutes at most. The project is not built yet. I can build as much space as is needed. I was roughly thinking, in inches, Length 16”, Width 12”, height 3”. Thank you.

 

Do all the leds come on at the same time, or are they put on at separate times?

 

Echoing Dodgydave's question, is this a simple static diorama in which you turn on the switch (or connect the battery) and all the LEDs come on and stay on for 20 minutes, at one brightness level, until you turn off the switch (or disconnect the battery)?

If that's the case, things are conceptually quite simple -- you put a resistor in series with each LED and then put all twelve of these resistor/LED sets in parallel. You can play around with the exact resistor sizes to get the brightness you want. Once you decide on your LEDs, we can show you how to get your initial resistor values and you can tweak from there. If you want to get a bit more sophisticated, you could put a trimpot (trimmer potentiometer) on each LED, allowing you to easily adjust the brightness of each LED in response to the surroundings (e.g., in a brightly-lit room or in a corner in a pretty dark room).

While you could get more battery life by carefully putting some of the LEDs in series, I would recommend against it if you only need it to be on for half an hour or so. The simplicity and/or individual adjustability is probably far more useful.

Assuming each LED ends up needing 20 mA, that's 240 mA. Three AA alkaline batteries in series can easily supply this much current and last for about 10 hours. A 9 V battery is also an option, though it would only last an hour or so.

 

Diffused LEDs will provide a general glow. Non-diffused LEDs will project a small intense beam....one that will leave spots in your eyes if you look at it directly in the bear.

Most likely, you'll want diffused LEDs, although a couple non-diffused might be useful for some effects.

 

Here's some general information that might be useful.

white LEDs use about 3vdc-5vdc each
green LEDs 1.6vdc-2.2vdc each
blue LEDs 2.5vdc-4vdc each
purple LEDs 3.2vdc each
yellow LEDs 2.0vdc each

So you can see that they use different voltages. The best power source would be 4 AA batteries since that would equal about 6 volts and could power even the highest voltage LED here. Buy a little bag of 200ohm and 300ohm resistors (1/4 watt) and simply attach 1 resistor in line with each LED, all connected to your battery pack individually. Play around with which resistor seems to give you the best light, maybe even use 2 resistors for some of the LEDs if that gives the effect that you like. Just a final note LEDs actually only work in one direction, so if the LED doesn't light up when you plug it together then just install it the other way, nothing will be damaged either. They are tough little lights

 

It's her uhhhh.... "intelligent nerd" husband here, thank you for the help everyone. I haven't actually done much of this stuff where I've planned the circuit myself, but I do know Ohm's Law and have dabbled with low voltage / simple circuits before.

Yes, it's a simple diorama where all lights come on. I will definitely wire the resistors in series to each light then parallel to the whole circuit. I'll also be using diffused LED.

Thank you for your awesome answers, I have a few more questions if you don't mind.

1) If I do a parallel circuit, I should be fine to have the different colours on the same circuit, right? Would I place the lowest "vdc" colour closer to the battery? Or would this even make a difference?

2) Regarding batteries, I think AA makes the most sense, just for ease of replacement? 4 AAs will produce 6v and I'm sure that will be enough. Would a parallel circuit change this? As I type this I realise that the resistors are what sort this out if I understand correctly.

3) So I would have 12 branches, one per light. All branches will have a resistor (I can calculate the resistor required using Ohm's Law). Is it worth connecting the two yellow lights on either side of the diorama in series within the parallel? Pardon my laymen's representation below but something like this? Or is that an unnecessary complication?

Battery
-> R1 -> Resister -> LED -> Battery
-> R2 -> Resister -> LED -> Battery
-> R3 -> Resister -> LED -> Battery
...
-> Rx -> Resister -> LED -> LED -> Battery

Again, thank you all so much for your help. You're awesome!

- "intelligent & nerdy" husband

 

Here is an LED series resistor calculator which may be handy.

If you have LEDs in series, forward voltage is the sum of the forward voltage of the LEDs. It's best not to put different color LEDs in series because the brightness at the same current may be very different.

The maximum current for small LEDs is typically 20mA but operating at lower current (say 10mA or less) will often provide adequate brightness and provide longer battery life.

 

1) If I do a parallel circuit, I should be fine to have the different colours on the same circuit, right? Would I place the lowest "vdc" colour closer to the battery? Or would this even make a difference?

No (discernible) difference.

2) Regarding batteries, I think AA makes the most sense, just for ease of replacement? 4 AAs will produce 6v and I'm sure that will be enough. Would a parallel circuit change this? As I type this I realise that the resistors are what sort this out if I understand correctly.

You want the four AA batteries in series -- then think of this as just being a simple 6 V battery.

3) So I would have 12 branches, one per light. All branches will have a resistor (I can calculate the resistor required using Ohm's Law). Is it worth connecting the two yellow lights on either side of the diorama in series within the parallel? Pardon my laymen's representation below but something like this? Or is that an unnecessary complication?

Battery
-> R1 -> Resister -> LED -> Battery
-> R2 -> Resister -> LED -> Battery
-> R3 -> Resister -> LED -> Battery
...
-> Rx -> Resister -> LED -> LED -> Battery

You certainly could do that. It ensures that the same current will flow in any LEDs that are in series. This could be a good thing or a bad thing, depending on what's important. The more you put in series, the longer your battery will last. But the more sensitive the current will be to the exact resistor value that is in series with them. Also, the amount by which the LEDs dim as the battery voltage drops will be more pronounced, but over the course of twenty minutes it shouldn't be too intolerable.

For reasons I spelled out previously, I'd recommend keeping it simple and just having twelve parallel circuits, one per LED/resistor combo.

 

With modern efficient LEDs, 10 mA can be painfully bright, but that may be what you need. You could go even brighter using "Superflux" or "Piranha" 4-legged LEDs; I think those will handle up to 40 mA (they're often used in vehicle tail lights). The best thing would be to try a selection of resistor values or use a variable resistor, in series with a fixed resistor so you don't accidentally turn it too far and apply infinite current.