Subject:
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Re: Need Electrical Help
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Newsgroups:
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lugnet.trains
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Date:
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Fri, 24 Oct 2008 01:21:14 GMT
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Viewed:
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12268 times
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In lugnet.trains, Tom Keenan wrote:
>
> I realize that this is an old post, but I jut found it...If I want to hook up a
> bunch of LED's (say they are 2.1 volt and I want to hook up 10) to a 9v system,
> what do I need to do? Only hook in four at a time or something like that?
>
> I could wire a whole house, but when it comes to small scale electronics, I am a
> complete novice.
>
> I have a LEGO train track going around my son's room near the ceiling. I am
> building a Santa Sleigh and rindeer to run on the tracks and I's like to light
> up Rudolph's nose with an LED as well as have several LED's along the other
> reindeer and the sleigh so that they look like traditional christmas lights.
>
> Thanks.
If the voltage is going to vary, don't use a resistor as current source,
consider a current regulator instead. That way the LED stays brightly lit over a
wide voltage range without getting burned out at max voltage. This works for
one or more LEDs in seires. The simplest and cheapest is shown here
<http://www.elecfree.com/electronic/fet-current-source-by-bf256/> The LEDs light
up at full brightness when the voltage exceeds the LED voltage by a small amount
and stays constant up to 18v or more. I use this for the headlights in my
trains.
You need a bit of overhead voltage, higher then the LED rated voltage, to pass
through the FET. If the track voltage is going to vary a lot, build your sting
of LEDs with this in mind. If you run 2 red LEDs(2.1v) in series, they won't
light up much at less then 4.2v. A single white LED(3v) lights up to full
brightness on the second 9v controller notch.
I bought my BF256c FETs at Jameco online. An eazy source for colored and white
LEDs is the LED Christmas strings. I pull the LEDs and toss the wire harness.
Most are the 5mm type(~ sixe of a technic hole). But you can also find the 3mm
(size of a hollow stud).
Mathew Clayson
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Message has 1 Reply:
 | | Re: Need Electrical Help
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| (...) Great idea. I hadn't thought about whether Tom was going to use a variable speed control. I just assumed batteries for some reason. Have you had any brightness issues with the seemingly low 15mA output for multiple LEDs or are you hooking 1 to (...) (16 years ago, 24-Oct-08, to lugnet.trains)
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Message is in Reply To:
| | Re: Need Electrical Help
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| (...) I realize that this is an old post, but I jut found it...If I want to hook up a bunch of LED's (say they are 2.1 volt and I want to hook up 10) to a 9v system, what do I need to do? Only hook in four at a time or something like that? I could (...) (16 years ago, 22-Oct-08, to lugnet.trains)
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