LED Wiring HELP!

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Jan 20, 2009
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I have a wild idea to wire a TON of LEDs into a 3-4" HPR. However, I am totally ignorant of how to go about doing the electronics. I am thinking of punching lots of little holes through the airframe for the LEDs to stick out of so that a clear tube is not necessary. I would either place the electronics into a payload bay or use an inner tube to protect them from the motor gasses.

Is this something reasonably easily done for the electronically challenged? What components (besides LEDs) are needed? I have followed the threads here on RF, but haven't understood exactly what is necessary... :(
Assuming you are usuing a 9vt battery, you will need resitors. 1K usually are used for this. Wire your LEDS in parrallel, each LED with its own resistor... You can buy LED's with built in resistors, but they cost more.
don't most or some LED's have a voltage polarity? I know they have some non polarity LED's....
LED's are, by definition, "Light Emitting Diode's," and as diodes, they only allow current to pass through in one direction. I recommend going over your plans with a friend in the electronics field who can make sure you're aligning them right.


Disclaimer: It's been 8 years since I took EE, so I may be a little off here.
Your project is perfectly fine and an easy build thou it will take some wiring time.
Doug gave some good basic info. I am flying an UpScale Nova Payloader with a BT-80 2.6" Clear mailing tube "payload section" containing 43 verious mcd rated LED's and a PNC-80K Led Illuminated by a single 12000mcd orange Led. the entire package is illumintated by a 3V lithuim battery. This same battery has flown in at least 6 flights.

you can set up your Leds to run an any battery voltage you like by using the information on the back of the LEDpackage and the following formula.
R (resistance) = Vbat (votage of the battery) - Vled (-voltage LED)
divided by C (Amps) usually in ma milliamps.
Example: 3v (battery) - 1.85v (from led pack) divided by .020 (20ma) = 57.5ohms resistor. Use the closest Higher available resistor value which for this example would be a 68ohm.

Heres a pic on the underside of my Niteflight UFO Illuminated by 24 leds and resistors, powered by a 3V lithium battery. In a test run this combination ran for over 6 hours.
there are a ton of pics of the other Night flight illumination pics in an earlier post in the low power forum "Night launches a fun Club activity"
I too am electronically ignorant. My idea is LEDs inside a clear payload running on a button cell. I don't know the first thing. I think I need someone to explain it in lamen--lamen's terms.

From my understanding I'm told I'll have to wire in series. i.e.: battery, Resistor, LED, R, L, R, L, bat.
Here's another source for ultra-bright LED's: <a href="https://www.lsdiodes.com">https://www.lsdiodes.com</a>. It also has a FAQ about hooking up LED's.

One thing about LED's - if you over-current them, say by hooking them up without resistors, they WILL blow instantly and permanently, and they won't show any external signs of damage. So if you're certain you've got everything hooked up right but it doesn't work, try a fresh LED from the bag - you may have inadvertantly blown it.
You are correct, the leds are in series but the number of circuits or strings of Leds is almost unlimited. I've run as many as 6,
12 led/resistor combination strings from a single 3v battery combination. The UFO is broken into 3 segments running back to the single 3v cell. Your power supply can be any battery type you'd like AAA's, AA's, C's D's or ilthium cells. 6, 9 or 12volt cells can alao be used, the choices are almost endless. You are only limited by your imagination and the space and weight lifting cap. you have to work with.

Heres a group of simple Led and or bulb combinations that might be of help
The over voltage burnout is very true, This is way we need to know the voltage we are going to use as a power source, and Most important we need to get all the data from the package back or info insert that comes with your leds. Once we have the Led operation voltage and milliamp rating finding the correct resistor is simple using the formual R= Vbat -Vled divided by C.

I guess I should have shown the visable side of the UFO it looks neat spinning at night:)
I would be inclined to wire the led's in parallel that way if one blows the rest would remain alight.

Taking an led's voltage at 1.2v and a current of 30ma, I would sugest a resistor of 680ohms, and remember that the led's are polarised.

Do I need to use a resistor with every LED? Whether I wire them in series or parallel? What kind of wire would be the best for running the connections? (I warned you that I was electronically challenged...)

I'm thinking that I will be trying to use a 9v battery so that I can easily velcro it in place and still have solid attachment points for the terminals.

Thanks for the help and advice! :D
It's best to use a resistor with each LED but in practice you can group like mcd values on a single resistor I've ganged as many as four 1.2 to 1.85V Leds on a single 68ohm resistor with only a minimal drop in mcd output and battery drain. In the Pic below each of the 3 - 3 led strings are connected to a single resistor as well as a 12000mcd orange led in the nosecone with its own resistor. all powered by a 3/8" dia 3V lithium cell. that's a BT-20 white plastic nose cone that flys on an Estes X-ray with an 13mm A3-4T motor.

For your first project I'd stay with a resistor per led, they are very inexpensive and easy to get, Radio shack still carrries them in 5 packs or you can purchase them on line from any of the electronics site in 100pks which are even more of a deal. Again I'd stay with the 1/2 watt, 5% tolerance, carbon-film, 68ohm resistors as a good starting point. Most of the Leds from Superbright range between 1.2 and 2.85 min. voltages @ 20ma.
hope this helps a little
Originally posted by RocketmanTM
What kind of wire would be the best for running the connections?

Good question. I was wondering that my self. What gauge wire do you use? Or can you just hardwire them together? Any thoughts, anyone?
Originally posted by mkmilion
Good question. I was wondering that my self. What gauge wire do you use? Or can you just hardwire them together? Any thoughts, anyone?

Get thyself a wire-wrap tool, and some wire-wrap wire from Radio Shack. No soldering necessary, except where you hook the wires up to your battery terminals and switches.

There is simply nothing easier with which to hook up LED leads.

Also, I use wire-wrap wire to rig up clusters for Estes igniters, an added bonus use for this tool.
Yeap! Vince is correct! If your new to soldering or simply don't want to mess with soldering, tie warpping is the way to go.
I use the finest copper bell wire (telephone wire) I can get my hands on for soldered applications, I have a few friends that supply me with leftover commerical phone installation wire bundles that are 22 & 24gage. It's great stuff if you can get some.
Radio shacks wrap wire is 30gage alum. and works well with their wrap tool. great stuff for some types of homemade igniters also. and/or igniter extensions for those hard to get at recessed motors like "the Point" and "Pheniox".
Personally I don't usually use wire warp connections on flight model units because of the potential for vibration/shock loosening of the conntections. However if the unit(s) are "packaged" well they should hold together for a good while, just make sure your battery and battery connections have some kind of mechanical restraint. You'd be amazed at the shock and vibration loads we put on these little paper models:)
Aside from there being some really great info in this thread, it always amazes me that Micromister has a photograph or 2 to go with WHATEVER topic is being discussed. :D

Okay, so I found packs of 25 LEDs for $6.99 at the local Fry's Electronics, but they are rated for 3V...Am I gonna smoke them if I hook them up to a 9V battery? I didn't have time to dink around and see if they had the proper resistors... How does one figure out the amps from any given battery? Without a meter that is...

Thanks to Micro for all the fantastic info so far!
Todd -

A URL is worth a thousand words!


p.s. ...the LED calculator links on this page are fantastic!

Also - even if you have some really bright LED's, nothing will
prepare you for the new "ultra-bright" LED's which put out
4,000 MCDs and above. Check them out, you will be completely
great Site Vince!
You'll note that is the parallel formula given earlier in this thead. sometimes it is easier to see with a drawing:)

a quick look at what your using: 9volt supply, 3V (forward voltage of you leds, & assumed 20ma operation, Each led in your project will require a 300ohm resistor. You shouldn't burn out anything. Good luck on the project, lets see pictures as soon as you get it fabricated.

When you've been building models for over 35 years, you gather a lot of photos of things you've done:) Honestly ya haven't seen anything.... There's a whole "first Fleet series of black & whites - mid 60's to late 1979", all I could affort back then, of models, flights, launch equipment, and techniques I haven't even scanned yet:). 3 or 4 100 to 500 pic albums of color pics of flight ect. also awaiting culling & scan. NOW I have a digital camera for more new static stuff, I just can't seem to catch a lift-off with the thing to save me:) Like the man said.. One picture is worth 1000 words, I hope including them doesn't come off as a bother to folks.
John - the photos sure don't bother me one bit. The images are one of the main reasons I like TRF in fact.

Just one last word on LED's - one easily overlooked aspect is the viewing angle shown on many LED data sheets. Many bright LED's focus their beam into a narrow (30 degree or less) cone, with a significant dropoff in brightness the farther off-axis you view it. So, the geometry of the LED's can significantly affect nighttime visibility as well.

"Must remember to spray my night-launch rocket with water repellant this year."
All LEDs have a maximum current specification. If you exceed this value, you will most likely destroy the LED immediately. It's probably best to plan to use a current that is 50-75% of the maximum rated current. That way you'll never blow an LED and get more lights to boot for a given batery size.

Different color LEDs have different voltage drops across them for a fixed current. RED LEDS have the lowest voltage drop, and Blue LEDs have the highest. If there were no losses, the voltage drop across a red LED would be 1.2 volts, a green LED would be 1.45 volts and a blue LED would be 1.9 volts. In practice these values are typically ~2 volts for red, ~2.7 volts for green and ~3.5 volts for blue LEDs.

There are lots of ways to connect multiple LEDs. The simplest is a parallel connection of single LED/current limiting resistor strings. If you are using a 9 volt battery, this methods wastes most of the battery power in the current limiting resistors.

For example, let's set the current to 10 ma. from a 9 volt battery. A red LED will have a 2 volt drop so you need to drop 9-2=7 volts at 10 ma through the resistor. V=RI or R = V/I = 7/.01 = 700 ohms. For Green the resistor value would be (9-2.7)/.01 = 630 ohms and for blue (9-3.5)/.01 = 550 ohms. If you wanted just a single red, blue and green LED this method will uses 30 ma.

A better way to go is to put a string of several LEDs in series and limit the string current with a single resistor. A string of a red, green and blue LEDs would require a resistor with the following value.

V rest = 9 - (2 + 2.7 + 3.5) = 9 - 8.2 = .8 volts. R = V/+ = .8 / .01 = 80 ohms. (A slightly greater resistor value such as 100 ohms would be ok since it is easier to get.)

By putting 3 of these three LED strings/resistor chains in parallel, you can power 9 LEDs verses the 3 LEDs in the first example using the same 30 ma of battery current. This method is much more efficient.

There are many other ways to do it even more efficiently but they require multiplexing of a many phase clock. It's not that hard, but you need to do some circuit fabrication.

You can get a lot of good information on LEDs and driving circuits at https://www.maxim-ic.com/Display.cfm and https://www.ledmuseum.org/

Bob Krech

I think the added pics are great. Keep it up. I'm jealous. I don't even have a 35 mm camera :D. One of these days I'll stop being cheap and buy a digital camera.

I'll check out the links and get to work. I'm thinking approx. a 12"x4" payload bay with 50-100 LEDs spaced roughly evenly about it for my BSD sprint. I'm also thinking of adding a strobe that is attached to the 'chute, preferably focused upwards into the canopy. I'll post pics when I get it done!
I just solder the LED/resistor string together making sure all of their polarity was right and used a brand new 9V to test. And no luck. Any ideas?
Originally posted by mkmilion
I just solder the LED/resistor string together making sure all of their polarity was right and used a brand new 9V to test. And no luck. Any ideas?

It would help if you provide a diagram of the circuit, with the LED types and resistor values.

Also, be sure to carefully check ALL LED's for proper orientation; flat side is the cathode and goes towards negative. If you have multiple LED's in series and just one is oriented backwards, current flow will be blocked (they are - after all - diodes... blocking reverse current flow is what they're supposed to do!)

If you're positive everything's hooked up right, and still nothing, check the current flow using a multimeter. No current flow? Disconnect the power source, and test each LED as a diode individually (provided it's a complete series circuit, the other components won't affect this test). By test, I mean either use the diode test feature on your digital multimeter, or if you don't have one of these, select a resistor to power a single LED with your power source, put this in series with your power source, and clip the leads to each LED (observing proper polarity) one at a time. If one or more LED's won't light, it's most likely been fried by either passing too much current or perhaps damaged when soldering.

Going back to the top of the previous paragraph, say you have current flow, but it's only a couple of milliamps. Double-check to make sure you're using a suitable resistor, as you may not be passing enough current to light the LED's. If that's the case choose a lower value resistor.

That's all I can think of for now, let us know how it goes.
One thing I do with my diode arrays is to put an "idiot diode" in circuit with them so as to stop accidental reverse wiring.
I use a small silicon diode, 50PIV, in the negative battery lead, if you make a mistake and connect the battery wrong, no current flow no damage.

I just solder the LED/resistor string together making sure all of their polarity was right and used a brand new 9V to test. And no luck. Any ideas?

A couple of quick thoughts

1. Do you have a multimeter? If so, you can test each segment independently. Unfortunately without knowing your circuit diagram, diagnosis is going to be sketchy. Each individual segment should be something like:

| |
| |
|------------(+)Battery(-) -----------|

This looks fine when I type it and lousy when I post it. Imagine a box, if you will :confused:

If you remove the battery and substitute a ohm meter thein if the leads are set one way, you should read the resistor value. The other way should read infinite. Alternatively measure voltage across the LED, it should fall with in the rated voltage shown on the spec.

One slim possibility is that you damaged the LEDs with heat from the soldering iron. I always use a heat sink between a semiconductor and a solder joint. A pair of metal hemostats is outstanding for this purpose.

One other possibility. Inexpensive electronics suppliers have been known to be a little less than precise in packaging. Make sure the color code on all the resistors is identical.

Finally check to make sure the polarity is correct (especially if you are placing these things in series.

I found out that the guy at Radio Shack had sold me the wrong type of resistors. Since he was the one that suggested them he gave me a full refund/exchange on the LEDs and resistors. I update you on the new ones.