You were up late Dervish!
My dad was talkin about it. He was wondering about making a moonlight affect on a coral reef aquarium.

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Do not connect them in parallel, use a serial circuit. The reason for this is that the LEDs might have different operational voltage drops and they would each draw a slightly different amount of current resulting in slightly different brightnesses. In serial, they all have the same amount of current running through them.

The circuit should look like this:

+ ---[Switch]---[Resistor]-- +[LED1]- -- +[LED2]- -- +[LED3]- --
[9V]
- --------------------------------------------------------------

The order doesn't really matter, but make sure that the LEDs are in the right way (they have +ve and -ve ends) or they won't work. Typically, the longer lead is the +ve one.

The resistor is needed to ensure that the LEDs don't draw too much current. The best way to find out is if you have the LED data sheet. Find out what the operating current (I_L) and voltage (V_L) values are. Then do (V_s - 3*V_L) / I_L = R. Find a resistor that's close to (but greater than) R.

LEDs typically require V_L = 2 V and I_L = 20 mA. V_s = 9 V in this case so R = 150 Ohms.

Note: Blue LEDs require 4 V usually. You would need another 9 V battery if this is the case. Once again, this information would be in the data sheet.

PM me any questions, I would be glad to answer them.

Disclaimer: I am NOT responsible for any damage or personal injury caused by following these instructions.

quote:

Originally posted by Jackson You were up late Dervish! My dad was talkin about it. He was wondering about making a moonlight affect on a coral reef aquarium.

Yeah bit of an insomniac, went to a lecture to day at 9.

You could use a variable resistor to dim it and stuff as well. Though I don't know how easy it would be to make it linear and over a proper range.

Depends how much you want to piss about with it really.

You may already know, but as LED's are diodes the current can only flow one way through them so they need to be connected the right way round.

And as far as I can remember from my Electronics A-Level (a couple of years ago) the short leg is negative and the long one positive.

Dont worry about personal injury. I'm sure a 9v battery wont do much damage

Will i need a circuit board to attach everything? And would i also need a soldering iron or is there another way?

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You can use strip/vero board you cut out (remove) connections using a dill bit even (ment to use a special tool, big drill bit does the same job though). Your probebly easiest to use an iron (I got a cheapo shit one from argos with all the other stuff for <£20, maybe borrow one?).

I've had 1,000 volts through me at one point, current limited though, just makes you look like a mong

Hmmm, i saw some kits on ebay (i'll try to find a link) for Radio controlled cars. Everything is wired and ready to go with a switch. Its was £7-50 i think. Only problem is that the cable length might be too short, would it be fairly simple to just lengthen the cable?

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No matter, i found someone on ebay that makes LED headlight units for remote control cars. He said it'll cost me about £6 including postage and will be delivered by Monday!...I know that may be expensive for the parts but i would have to buy all the equipment (soldering iron) if i wanted to make it myself...and i'd still probably bugger it up

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