Resistors and Multiple LEDs

cjharrisman · Post by **cjharrisman** » Sun May 18, 2008 6:28 am

I am kinda new to lighting my models, and i had a thought, is it possible to tie multiple leds to one resistor, say 5 or 6 leds to a single one?

fsgray · Post by **fsgray** » Sun May 18, 2008 12:04 pm

Yes, if they're wired in series. Here are some good sites I've hearned from:

http://www.theledlight.com/ledcircuits.html
http://ledcalc.com/
http://www.starshipmodeler.com/tech/mh_led.htm
http://white-leds.co.uk/led-wiring-guide.htm

USS Atlantis · Post by **USS Atlantis** » Sun May 18, 2008 12:28 pm

fsgray wrote:Yes, if they're wired in series. Here are some good sites I've hearned from:

http://www.theledlight.com/ledcircuits.html
http://ledcalc.com/
http://www.starshipmodeler.com/tech/mh_led.htm
http://white-leds.co.uk/led-wiring-guide.htm

One thing you have to watch out for is differing Voltages

LED's usually come in two varieties - 2v and 3v

Bad Things happen if you try to mix the two in a single string

Personally, I try to refrain from having more that one color per resistor, that way the voltage and current values are identical - on the rare occasion, I'll mix two colors, but only if the values are the same - see my Nav Blinker circuit on my build page for an example of this.

kitty · Post by **kitty** » Sun May 25, 2008 5:39 pm

not realy advisable, if the resistor breaks, you will loose 5-6 Leds at once.
One of the reasons why putting multiple LEDs or Bulbs in serie is bad practice.
If you stick to 1 resistor per led then only one LED wil fail if a resistor goes and frankly the chance of a resistor failing is bigger than the chance that a LED fails, providing you stay within the voltage and current limits of the LED

DLMatthys · Post by **DLMatthys** » Wed May 28, 2008 8:54 am

SCC-7107 USS Atlantis wrote:
Bad Things happen if you try to mix the two in a single string

I agree!
But I am also STUMPED

I want to combine a White or Blue (30ma, 3.5v typ) with Red or Amber or Yellow (20ma, 2v typ) on the same circuit...parallel. Does anybody with a design degree or better knowleged than I, know how to combine these colors to blink well enough to be visable at the same time?

Despirate is my seach at DigiKey to find T-1 (3mm round) a high bright Orange LED (3) plus Blue LED (2) combination to come on at the same time on the same paralle circuit. I think the key to sucess is to find both type LEDs with the same current and voltage values...

Or is there a resister that could be wired in series with one of these two to even the voltage out, to light up at the same time.

The goal is to have this combination work of TOS Enterprise Waddle Warp discs. A 4017 chip combined with (3) 2N222 transisters.
Some etched circuit board examples shown here:
http://www.hobbytalk.com/bbs1/attachmen ... 1197905745

I would hope it would be a simple solution befor takeing a look at a whole new redesign of the main boards. If any blue LEDs that work at 20ma 2v we would be close to a perfect world...

Umi_Ryuzuki · Post by **Umi_Ryuzuki** » Wed May 28, 2008 12:14 pm

If you are wiring in parallel then its a non issue.
The voltage to all the LED are constant.
Just put the appropriate resistor in at each LED, and
wire your 555 timer circuit or other blinker timer in at the
head of the string.

I wire Red, green, white, and yellow up on common circuits all the time.

http://www.rcgroups.com/forums/showpost ... tcount=169

DLMatthys · Post by **DLMatthys** » Wed May 28, 2008 1:53 pm

[quote="Umi_Ryuzuki"]
Just put the appropriate resistor in at each LED, and
wire your 555 timer circuit or other blinker timer in at the
head of the string.

Yep Umi...that makes sence.
The situation on this WWB board is that it get's 4.5v - 6v input to the CD4017 pin 16. From pins 2,3 & 4 ( 1, 0, 2 ) is a single 182 ohm resister on each befor getting into the middle pin of a 2N222.

I'm thinking now that resister should be lowered to be 100 to 110 ohm. That could be more friendly-powerfull option to get more voltage and current into the 5 LEDs (orange) up to the dome discs. So what I have goin' on is the one resister. Two or three of those orange LEDs I want to use blue.

I'll resolder in a lower LED... then see what happens

USS Atlantis · Post by **USS Atlantis** » Wed May 28, 2008 5:03 pm

Umi is correct - parallel circuits are a non-issue

You can drive several different LEDs with differing voltages off a single output of a 4017, a 555, or even an OP-AMP

Just run the calcs for the resistors as if each LED was alone on the circuit - same thing if you have multiples of each LED

jwrjr · Post by **jwrjr** » Wed May 28, 2008 10:34 pm

Just make sure that the device you are using to drive the leds is capable of sourcing the amount of current needed by the leds.

RossW · Post by **RossW** » Mon Jun 02, 2008 2:44 pm

Bad Don - it's Waddell

The problem in my circuit is that each output from the 4017 drives 3 LEDs on each nacelle, so 6 in total (It could be 5 LEDs/output so 10 in total - been a long time). If you mix LED voltages on one output then you need to wire different resistors in series to each LED on the nacelle disk, and there's not a lot of room to do that.

USS Atlantis · Post by **USS Atlantis** » Mon Jun 02, 2008 6:30 pm

RossW wrote:Bad Don - it's Waddell

The problem in my circuit is that each output from the 4017 drives 3 LEDs on each nacelle, so 6 in total (It could be 5 LEDs/output so 10 in total - been a long time). If you mix LED voltages on one output then you need to wire different resistors in series to each LED on the nacelle disk, and there's not a lot of room to do that.

Unless you do it in the Engineering Hull - which is where I'm placing my circuit board for the 18" AMT-TOS - all the resistors and IC's are on the board, only thing in the Nacelles is the LED's themselves

tetsujin · Post by **tetsujin** » Tue Jun 03, 2008 11:17 am

SCC-7107 USS Atlantis wrote: One thing you have to watch out for is differing Voltages

LED's usually come in two varieties - 2v and 3v

Bad Things happen if you try to mix the two in a single string

Not true. If you wire up 2V and 3V LEDs in series, what will be constant through that circuit is the current - so long as the amount of current running through that circuit is within each LED's operating range, you're fine. Each LED will then drop a certain amount of voltage - if the current is within its operating range then the voltage will be, too. The only thing about putting a bunch of LEDs in series is that your source voltage has to be high enough to drive all those LEDs, or else the string won't light up.

Different voltage LEDs in parallel, though - yes, bad idea. Can't do it unless each LED has its own resistor.

DLMatthys wrote: I want to combine a White or Blue (30ma, 3.5v typ) with Red or Amber or Yellow (20ma, 2v typ) on the same circuit...parallel. Does anybody with a design degree or better knowledged than I, know how to combine these colors to blink well enough to be visible at the same time?

Desperate is my search at DigiKey to find T-1 (3mm round) a high bright Orange LED (3) plus Blue LED (2) combination to come on at the same time on the same parallel circuit. I think the key to success is to find both type LEDs with the same current and voltage values...

Have you tried Mouser...?

I wouldn't bother trying to find LEDs with the same ratings, though. Better to just give each LED its own series resistor - experiment with values until you find ones that put the two LEDs at roughly the same light level (if that's your goal)

If there are 2V blue LEDs out there, they are odd beasties indeed. All the whites, blues, etc. I've seen are in the 3V range. Even if you managed to find some, I wouldn't necessarily rely on being able to find more of them again in the future. :)

If space is an issue, consider surface-mount components. Since you have a board and all, surface-mount should be relatively easy to deal with... Not like having the components dangling off 30 gauge wire...

jgoldader · Post by **jgoldader** » Fri Jun 06, 2008 8:33 pm

tetsujin wrote:
SCC-7107 USS Atlantis wrote: If there are 2V blue LEDs out there, they are odd beasties indeed. All the whites, blues, etc. I've seen are in the 3V range. Even if you managed to find some, I wouldn't necessarily rely on being able to find more of them again in the future.
Unless somebody's gone and changed physics on me, a 2V blue LED isn't possible. 2V is enough to produce 620 nm photons--reddish light. You'd need to go to 3V to produce 410 nm photons--bluish light. White LEDs that are really a combination of several different semiconductors that produce red, green, and blue light ought to take 3V or so. (You could get a blue LED by painting a white LED blue, but that would still take 3V minimum.)

There's a really nice classroom experiment for an AP Physics-type class using LEDs to find Planck's constant by relating the turn-on voltage to the color of the LEDs. Bluer light=higher frequency, therefore bluer LEDs simply need higher voltage, since E=hf=e*V, where V is the voltage, e is the electron charge, h is Planck's constant, and f is the frequency of light produced by the LED. Find the turn-on voltage for LEDs of a variety of colors, measure the peak frequency of the LEDs, plot e*V vs. f, find the slope, which is h.

For $5 worth of LEDs, you can find the value of the constant behind quantum mechanics. It's a beautiful thing.

Jeff