Simple LED electrical project

[mindmaniac]

I have very little electrical know how. I want to build a simple circuit that will light two or three led lights in which I can just tap in from power from another running device in my fishtank like the pump. Can anyone tell me what I would need and how I would set it up.

For those who don't know a moonlight(LEDs) are used at mimic the brightness of the moon in the tank to put less stress on the fish and also so you can still see it while not making things extremely bright.

If I do all this myself I'll end up buying some leds at radio shack and wire them up to something and start myself on fire.

 

[PsYcHoCoW]

Do you know what voltage and how much current the other devices deliver? Also, are there plugs from a power source that you can use? I'll draw a quick schematic for you in a sec, the application itself isn't too hard

LEDs don't require a whole lot of current to light up, but that has to be put in relation with the kind of power source we have.

It could also be done easily with batteries...

/me goes to drawing board (aka Protel)

 

[Harvey]

It sounds like an easy project to design, but you need a much better description of what you want it to do and what kind of power is available.

 

[PsYcHoCoW]

Here's how I think the wiring should be: http://www.9bit.com/vrheaume/schem.jpg

The first resistor is there to prevent the diodes from suffering of overcurrent feed, we'll calculate its value when we know what source voltage we're using...

The 2nd component is called a potentiometer, in that particular wiring it's acting as a rheostat ; it can be used to make the current vary, thereby changing the intensity of the LEDs

After that, the three LEDs are simply wired back to back. You just need to make sure you get the polarity right : If you reverse a single LED, none of them will light up (because reverse diodes don't let current flow...)


We could remove the potentiometer if you don't plan on varying the intensity of the LEDs ; I think a switch could be useful though...

 

[bobsmith1492]

The motors on the pumps probably run on just a few (12?) volts DC. If so, all you'd have to do is strap a resistor and the LEDs across the power to the motor and voila; light. If they run on low-voltage AC, it would work also. However, if they run on 120V, I don't think you'd want to hook an LED up to that unless you used a transformer first to get it down to like 6-12 volts.

You could just use a neon lamp rather than LEDs; you can just plug that into the wall.

Also remember you NEED a resistor to limit the current to the LEDs or else they'll fry instantly. Trust me; I've done it way too many times.

 

[mindmaniac]

Okay, I've found a power sourse a 9V AC adapter. I've picked up a bunch of blue leds and some 150 milli-ohm resistors. Can someone draw me up the schematic?

 

[DrPizza]

It converts 120V AC to 9V AC
(just making sure it's not 9V DC)

Because you are supplying AC to the LED's, they will be on only 1/2 the time.
This isn't a problem, because it'll be pretty simple to just make to similar parallel circuits, similar to the circuit provided above.
What's the resistance of the blue LED's?

edit: I actually have done this with 2 different colored LED's to demonstrate AC.
With a resistor and LED wired in parallel to another resistor and LED (with the LED reversed), it alternates between which light is lit. Stationary, it looks like an orangeish light. But, when I spin the cord around in a circle, it makes a circle of alternating red and yellow/green stripes.

 

[DrPizza]

Another think that you may find nice to give it a cleaned up appearance when you're done is some shrink wrap stuff (forget the name) - put a tube of that over the connections you solder (or twist together), heat it slightly, and it shrinks nice and tight around the connections.

 

[bobsmith1492]

Ok, a 150 milli-ohm resistor is nothing; they don't even make those except maybe for some strange applications - something's wrong there. For an LED and a 9V supply, you'd want at least 180 ohms, which would give you 50 milliamps across your LED given 9 volts input. Check the stats on the LED to make sure it can handle the current that would be provided (V=IR).

To wire it up, just hook up one terminal of your LED to the resistor and the other to the power supply; the other wire from the resistor goes to the other terminal of the power supply.

------RESISTOR-------LED-------POWER---
|_______________________________|

If it is AC, polarity won't matter; if it's DC, you would have to reverse the LED if it doesn't work.

 

[mindmaniac]

Originally posted by: bobsmith1492
Ok, a 150 milli-ohm resistor is nothing; they don't even make those except maybe for some strange applications - something's wrong there. For an LED and a 9V supply, you'd want at least 180 ohms, which would give you 50 milliamps across your LED given 9 volts input. Check the stats on the LED to make sure it can handle the current that would be provided (V=IR).

To wire it up, just hook up one terminal of your LED to the resistor and the other to the power supply; the other wire from the resistor goes to the other terminal of the power supply.

------RESISTOR-------LED-------POWER---
|_______________________________|

If it is AC, polarity won't matter; if it's DC, you would have to reverse the LED if it doesn't work.

I'm just working off of memory, all I remember is 150 somewhere on the resistors, you are probably right. Since I am working with AC power source and LEDs operate well at 3v what would be the best way to hook them up? I was thinking of using three or four parallel circuits with three LEDs in series in each one. If I did that would I still need the resistor?

 

[PsYcHoCoW]

You always need some resistance when working with diodes, otherwise... short circuit

The schematic I drew in my 2nd post should work...

Each LED takes up around 1.4 volt because of their semiconductor effect. You want to limit the current going through them to around 30 milliamps to the LEDs so they don't blow up, and so they produce enough light...

If you have three LEDs: 9V - (1.4V*3LEDs) = 4.2 volt
so 4.2 volt will be spread across the wire (short circuit if there's no resistance)

V/I = R
4.2V/30mA = 140ohm

The 150 ohm resistances you have will make sure a little less than 30mA will go through, so the LEDs are sure not to blow up.


Remove the potentiometer from my drawing and that's the circuit you should make for three LEDs, and you can create parallel circuits with the same battery if you need more groups of three LEDs, as you said.

 

[piasabird]

Super bright LED's use about 3-4 volts at milli-amps, so 4 of them would be about 12 Volts.

http://www.kaotica.com/frag/diy/moonlight/