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Old 06-25-2005, 02:18 AM   #1
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moonlights

i just ordered these lights the other day.
http://www.lc-led.com/View/itemNumber/94
data sheet http://www.lc-led.com/products/500tb4df.html
i am wating to make a 5 string led light with a pod. im not quite sure what power supply or resistors to use. i was asking on another website and they said you only need 1 resistor at the end of the series but other places i've seen one on every led. also whats the best pod out there that i should get? and in a older post i was reading about the photosenitive switches, are there any good ones out there i could get?
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Old 06-25-2005, 10:50 AM   #2
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I recently put together a set of 10 DIY led moonlights from a kit that I had ordered. Those instructions said to put a resistor before each led, not just one. They resistors were 22ohm 1/4 watt metal film resistor 5%. And the power supply was a 4.0v DC Transformer 700ma Input 120V 60Hz. If you search through the DIY Projects forum, you will find a couple of recent how-to threads.
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Old 06-25-2005, 12:49 PM   #3
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well before i start the electronics, people should head over to
http://www.lsdiodes.com/ for .45cents a piece they have blue leds at about 5000mcd, they run on about 4.2 volts which is bit higher than you purchased but the price is so much better. i don't work for them, i just like getting deals.

the reason some people use 1 resistor, or a resistor on each led has alot to do with the power supply they are using or preference. if they are using 1 resistor, then they are just using it as a current limiting resistor, and should have the leds in series with each other. the theory behind that is, the resistor will trim the incoming voltage / current source, and make it suitable for the leds. this is done when they have actually have enough voltage for every led.

series or parallel hook ups - if you build the circuit with leds in series (one leg tied off the last led leg) the current will be locked between the leds (each led will receive the same current) but the voltage drops for each led can change. this is handy if your mixing leds that have different voltage requirements or a large supply (if each led needs 3volts, and you have 5leds, then you will need a combined voltage of 15volts for series) or you build the circuit with leds in parallel, where each led is tied leg by leg off the last. so they appear to be parallel. i can post a pic showing this if you need. the theory behind having leds in parrellal, voltage is locked across all the leds but current can change if needed between the leds. and the reason you see a resistor on each led is make sure its receiving the right current and partially for some protection. most people prefer parallel hook ups for leds projects, and usually it is to keep the project as cheap as possible and find a power supply that supplies just enough voltage to the led to turn on and the same voltage can turn on many leds.

resistor selection is dependent on the power supply used. i can give you the formulas or once you make up your mind on the voltage/current of the power supply i can do the math for you. and then you will have your answer. i would recommend finding a 5v dc transformer, or a 12v if nothing else. also a great place to find these is from an old cd player you don't use anymore, or some other small electronic consumer good you no longer need, or have a use for. i would just recommend you don't go over the 12v range unless your going to build in series.

photosensitive switches, are manufactured by a bunch of different companies, and all pretty much stick to a tried and true method. there isn't really any great benefit choosing one over the over, unless the cost difference is substantial.

i am a little confused what do you mean by pod?
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Old 06-25-2005, 01:20 PM   #4
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i got mine at one penny for like 15 5000mcd. i accidently got the blinkers and i wasnt home in time to change the order. on ebay its like 5.01 for like either 20 or 30ish leds
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Old 06-25-2005, 04:27 PM   #5
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i was told to get a 18v source for the series and i ment pot (Potentiometer) sorry for the typo
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Old 06-25-2005, 07:15 PM   #6
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well if each led needs 3.2 volts a peice, and you have 5 leds then you will need a source of at least 16volts, 18v to have a cushion. building the circuit in parallel will reduce the voltage requirement to about 3.2 volts. again i would recommend building the circuit in parallel, sure it will require a restistor for every led, but reistors are dirt cheap.

a pot for this circuit should be about 25k ohms, the dimming effect of the pot should be pretty gradual, which is what you want.
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Old 06-25-2005, 08:51 PM   #7
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ok what are everything i would need for a parallel? which restistors, ect. is there anywhere i can get the pot, switch and restistors at the same place? so i can get a small powersupply? which one would you recommend
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Old 06-25-2005, 09:30 PM   #8
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Quote:
Originally Posted by mentallylost
They resistors were 22ohm 1/4 watt metal film resistor 5%. And the power supply was a 4.0v DC Transformer 700ma Input 120V 60Hz.
Not sure about the pot. Everything else came from www.ledwerx.com
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Old 06-25-2005, 10:07 PM   #9
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Current limiting resistor calculator..
http://metku.net/index.html?sect=vie...calc/index_eng
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Old 06-26-2005, 12:24 AM   #10
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To find the value of the resistors needed, you need to pick a voltage source (5v, 12v, 18v, etc) before you can use the formula below.
R = Vs - VL / IL

R is the resistor you need in Ohms
Vs is your supply voltage in volts
VL is the LED forward voltage drop in volts, or how much voltage you will need to turn on the led
IL is the LED forward current in Amps, how much current the led is rated to handle.

lets say you had a 4volt source, and the led needed 3.2 volts and 20ma (milli-amps) and you had 5leds to power.

so R = (4v - 3.2) / 20ma
R = .8v / 20ma = 40ohms
R = 40ohms / 5 (number of leds)
R = 8 ohms
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