Introduction: LED Disco Light in a Jar!

Picture of LED Disco Light in a Jar!

This one of my entries for the Let It Glow! Contest.

Here is a nice, simple instructable for anyone just starting out with LEDs, soldering and electronics. It uses basic parts, with no mucking about with microcontrollers or timers (as fun as those are!) You can build one in an evening if you have all the parts ready to go.

But what is it? The LED Disco Light in a Jar is exactly what the name implies. Over a dozen RGB LEDs in a mason jar, frantically changing colour in a completely random pattern. It's a neat light effect for your next party, or you can use it to entertain a baby for quite a while!

See the last page for videos.

Step 1: Parts

Here is what you need to build the LED Disco Light in a Jar:

1 mason jar, jam jar or anything with a suitably wide neck and a metal cap

1 switch

1 4xAA battery holder, in a 2x2 configuration

1 9V battery snap (mates with the battery holder)

24 RGB fast or slow-change LEDs*

12 10 ohm resistors

some solid 22 gauge wire

some heatshrink

perfboard or make your own printed circuit board**

some 25mm aluminum standoffs and matching screws

Glass Frosting Spray (optional)

  • These LEDs have only two pins, and when power is applied they automatically cycle between red, green, blue, and combinations thereof. You can find them on eBay from various sellers in Hong Kong and elsewhere.

** Making your own PC board isn't tricky, and if you know how to make them I recommend it compared to a perfboard. However, explaining how to make one diverges too far from this Instructable.

Step 2: Tools

You will need these tools to build the LED Disco Jar:

Soldering iron and solder

Heat gun or carefully controlled lighter

side cutters

"helping hands" clamp (optional, but makes things much easier!)

small needle-nose pliers

wire strippers


hot glue gun

something to cut perfboard or PC board

a sharp knife

PC board manufacturing kit (only if you're making a PC board)

Step 3: Make the LED Branches

Picture of Make the LED Branches

My LED Disco Light used 24 RGB LEDs. Yours may use more or less, depending on the size of the jar you've got. The 24 LEDs are arranged in 12 branches, each comprised of a single current-limiting resistor and two LEDs, all connected in series. Each LED receives about 3V, as dictated by the LED's datasheet. Don't exceed this value!

Those 12 branches are then connected in parallel with each other, so that each branch receives about 6V (3V + 3V + a nominal amount across the resistor).

You may want to start by "frosting" each LED using a piece of 800-grit sandpaper to diffuse the light a bit.

I spaced the LEDs in each branch at a random distance, so that when they were place in the jar they would appear randomly placed. Try to make a wide range of branches, but also make sure they will fit inside the jar!

The assembly is relatively straightforward. Start with the resistor, twisting a bit of wire around one lead and soldering it down. This is where the "helping hands" clamp comes in handy; the pieces tend to move around! Then solder an LED to the other end of that wire. Solder another wire, then the second LED. Finally, solder on the last wire so that it reaches all the way back to the resistor.

To anyone who has played with LEDs this will seem obvious, but to beginners remember this: OBSERVE POLARITY! LEDs will only light if connected in the right direction, and while nothing will blow up if you hook them up backwards they certainly won't light and you'll be sad. The LEDs have a longer lead (positive) and a shorter lead(negative); when I made my Disco Light I made sure that the long lead was towards the resistor on every branch.

Step 4: Finish the Branches

Picture of Finish the Branches

You should now have a number of branches (in my case, 12). On each one, place a short piece of heat shrink over the resistor. This helps keeps the wires together and makes testing and assembly easier. Shrink the heat shrink with a heat gun or a lighter. If you use a lighter, be careful not to scorch anything!

Step 5: Test the Branches!

Picture of Test the Branches!

Before you proceed, it's a good idea to test each branch to make sure it works! The easiest way is using a breadboard and a power supply, but you can hook up each branch to the batteries individually instead.

Step 6: Make the Circuit Board

Picture of Make the Circuit Board

If you're lucky enough to have a PC board etching setup, this part will be easy.

Instructions if you are using a PC Board:

1. Cut out a piece of copper-clad board that will fit inside the neck of the jar.

2. Using an etch-resist pen (or in my case, a bottle of nail polish my wife didn't want anymore) draw two concentric circles around the outside edge of the PC board. Make sure there is enough room in the center to mount the battery holder!

3. Etch the board

4. Drill 1/32" holes in the tracks at regular intervals around the board, one pair of holes for each branch, and an additional set of holes for the battery/switch.

5. Drill three more holes approximately as shown, for mounting the standoffs and to pass a wire through the board.

Instructions if you are using perfboard:

1. Cut a piece of perfboard that will fit inside the neck of the jar.

2. Drill three holes in the board in approximately the same place as on the PC board.

Step 7: Build the Lid

Picture of Build the Lid

You should drill the holes in the lid now, so you can use the PC board as a template. Place the PC board on the lid and trace through the holes you drilled. It's easy in my case, since the lid comes apart as two pieces on a mason jar. Drill the holes the same diameter as the ones on the PC board.

Next cut a hole for the switch. I used a rectangular switch so I had to (very carefully) cut the hole for it using a sharp knife. If your switch is round, you can just drill a hole.

You may also mount the switch and attach the standoffs at this point. To prevent the switch from moving I glued it in with hot glue.

The standoffs attach the PC board to the lid, and provide spacing for the switch. The length of the standoffs was chosen to match the height of the switch. In this case, 25mm standoffs were chosen to give enough clearance for the switch, which extended about 22mm below the lid.

Step 8: Solder the Branches Onto the PC Board

Picture of Solder the Branches Onto the PC Board

Here's the fun/tricky part. Solder each branch onto the PC board, again observing polarity. You may want to mark each circle as the "positive" and "negative" rail beforehand, so you don't end up soldering a branch in reverse. Try to alternate the branches so you don't have any LED directly beside another.

If you're using perfboard, glue the branches in place first, then solder the "rails" in two circles around the board to connect the branches.

Once all the branches are soldered in, you can hot glue the battery holder in the middle. Make sure it doesn't cover any of the drilled holes.

Step 9: Wire Up the Switch

Picture of Wire Up the Switch

Almost done! Now we're going to wire up the switch. Take the 9V battery snap (or if your battery holder has leads instead of snaps, the leads from the battery holder) and solder the black one to the negative rail on the PC board.

Pass the red one through the large hole drilled in the PC board and up to one terminal on the switch. Solder in on - it doesn't matter which terminal it gets soldered to. Grab a piece of wire and solder it to the other terminal on the switch. Pass it through the hole and solder it onto the positive rail of the PC board.

Load up some batteries, and switch it on! It should light up now.

Once you know that everything works, you can attach the lid to the PC board. Line up the standoffs and insert screws from the other side of the PC board. Everything should hold together tight.

Step 10: Final Assembly

Picture of Final Assembly

Now just drop the completed light array into the jar, and tighten the lid. Go ahead, turn it on and make sure it's still working!

Oooooh, shiny!

If you like seeing the LEDs through the glass, then consider this project done. However, if you've prefer a bit of mystery, you can frost the glass using glass frosting spray or glass etching cream. I used Rustoleum glass frosting spray. Frosting the inside of the jar hides the mechanics of the Disco Light, and helps diffuse the light a bit.

Spraying the inside of the jar is messy. Protect the outside using masking tape, and spray a coat inside the jar every few minutes as per the directions on the can. You'll probably find that the frosting spray isn't drying very quickly - I used a heat gun to dry the frosting inside in no time. It will take a few coats to hide the innards. Using white wires and painting the battery holder white will further obscure the contents of the jar.

Step 11: Videos!

Picture of Videos!

You're done! This light costs less than $10 to make, even if you buy all the parts new. It's great for jazzing up a party, giving as a gift, or entertaining babies (as you can see in the pictures below!)

Supplier list:

LEDs: eBay, seller was 'topbright88'

Other parts: Sayal electronics (an electronics components store in southern Ontario)

Small mason jar: Free from my mother in law (thanks!)


PattyP17 (author)2016-08-23

I am a crafter and tend to be smarter than the average bear, but I've never learned anything whatsoever about electronics. I'm highly skilled in other areas but not this. It's been decades since high school and I must admit science class was a snooze fest at that time and the coach teaching the class skipped whole chapters in Physical Science. I'd love to get started on an easy LED project, but not sure if this one is even too advanced for a total noob. I mean I can do things like use a soldering iron, solder & repair copper water pipes, and have been a silversmith, more. I've rewired lamps, but that's about the extent of my "electrical knowledge". I understand most of this instructable, and would like to extrapolate to a same-color-LED not-in-a-jar application, but there are things said that assume I know more, like what kind of switch, assuming they come in different sizes/voltages(?). Can you recommend something like a "For Dummies" place to start for a total noob that only knows how to screw in a 110v light bulb? I am familiar with most of the components you mention. I even have some heatshrink I bought at an electronics supply store to make tubing necklaces. I just don't have any electrical "sciency" knowledge and honestly don't want to study for two weeks before I can make something. I don't expect anyone here to educate me, just point me in the right direction to get started, please? I love this cool project.

Adzuom (author)2010-10-17

hey jeff-o I followed your instructions (except for the pcb, I just wired all the +ves and -ves together) and it worked out excellently.

I used a nice cut glass vinegar carafe I got from St. Vincent de Paul's and used slow colour changing LEDs with a 6V power supply.

Thanks so much for posting, I really like my lamp and your instructions made it easy and fun.

If anyone is curious about how it looks in motion, reply and I can post a vid to Youtube.

Looking forward to my next project - question is, does mineral oil and UV reactant paint mix?

jeff-o (author)Adzuom2010-10-17

Looks great, nice work!

Regarding mixing mineral oil and UV paint... Hard to say, so I guess it's up to you! You could also try mixing other UV-reactive liquids, like highlighter marker ink and glow stick fluid. Be sure to get your proportions right, though. From what I've read the concentration can't be too low or high, or it won't work.

itjmiller (author)2010-06-23

How did you make the PCB with a bottle of nail polish? I don't understand. Any guides you recommend for this step? I just started with all this stuff, and I've watched people make PCB's before, but their process was over complicated.

jeff-o (author)itjmiller2010-06-23

Easy! I just painted the pattern on the bare PCB. The result is far from pretty, but it works. Nail polish easily resists the etchant, whether you're using ferric chloride, ammonium persulphate, or muriatic acid. When you're finished etching the board, it comes off easily with nail polish remover. I still use nail polish for touchups on boards made with the photo resist and toner transfer methods.

mastover (author)2009-07-29

How long does the 9v last? Looks great!

jeff-o (author)mastover2009-07-29

It actually runs on 6V (4 AAs in a holder with a 9V connector). I'm not sure how long batteries last in it, I gave it to a friend as a gift before the first set ran out. Based on calculations alone, a 2000mAh battery (pretty standard for regular alkalines) would last over 16 hours.

knektek (author)jeff-o2010-03-09

Dude, i can get rechables that are 4700mAh. four for £8.00, lasts for about a year! even whan frequently used. On my camera about a months worth of photos on holiday. On ebay!

jeff-o (author)knektek2010-03-09

Oh yeah?  That just shows how up-to-date I am!  Ha!

Well, 4700mAh AAs would indeed power it for much longer.

Gakki (author)2008-10-06

Is it possible to combine this with th esunjar to make this solar?

jeff-o (author)Gakki2008-10-06

Unfortunately no, for two reasons. The first is that the PWM output from the solar light used in the sun jar interferes with the automatic RGB switching of the LEDs, effectively "resetting" the LED to its first colour (red) over and over. The second is that all those LEDs consume more power than the solar light circuit can supply. At least, that's how it was with the solar lights I have (dirt cheap ones). It might work OK with a larger solar light.

Gakki (author)jeff-o2008-10-06

Awwww.... That makes me a sad panda, but thanks for the explanation.

jeff-o (author)Gakki2008-10-07

I must emphasize that my tests were done using the cheapest solar light I could find, the type that use a single LED and a single AAA battery. A larger unit may work fine - you'll just have to try it and find out! Isn't that exciting? :D

LordOlimar (author)jeff-o2009-04-29

Is it that each individual LED consumes more power than the solar light circuit can supply? Or is it that all 24 lights together consume more power?

Basically, could you do this with one of the cheaper solar lights but just use less LEDs?? (I'd love to be able to do this with a solar light lol)

jeff-o (author)LordOlimar2009-04-29

Hmmm, you might be able to run 6-10 LEDs from a single solar light circuit, though with a shorter runtime. The big problem is the PWM output from the solar light circuit. It basically continually resets the RGB LED's internal controller, so that the light is always at the "first" colour in the sequence (usually red). If you wanted to make the disco light solar powered, you'd have to skip all the energy-saving PWM stuff and drive the LEDs directly from a bank of 3AAs. There is a great collection of solar LED circuits over at

Zippy_Pyromaniac (author)2009-01-17

Nice instructable! For the shrink wrap you could use recycled PET bottles from - wiley's instructablenk wrap you could use recycled PET bottles from wiley's instructable -

jeff-o (author)Zippy_Pyromaniac2009-01-17

Unfortunately, the wires here are far too small to use that method. I recommend using regular heat shrink tubing of the correct size.

Zippy_Pyromaniac (author)jeff-o2009-01-17


rerrett (author)2009-01-15

suggestion: youtube. ty

cameron59715 (author)2008-11-16

Hey, thanks for posting the design. I bought some slow flash RGB LED's on eBay . The "datasheet" on the eBay listing listed a voltage drop of 3.6V. All the LEDs of this type listed on eBay had the same voltage drop. I am just wondering if you had the same experience with the voltage drops on these LEDs being a little lower than listed. Thanks again. If you're interested, I have a glueless disco jar design. Bolt on the AA holder through the battery contact grommets. Isolate the contacts with nylon standoffs. What do you think?

jeff-o (author)cameron597152008-11-17

Wow, that's an impressive drawing! That would certainly work as well. One could also use a small square of velcro, to make the battery holder easily removable. The LEDs you have will probably work just fine on 3V each - but test them to be sure. I've found that the specs on Chinese-made LEDs can be wildly divergent, to the point that I never fully trust the "datasheet" posted in the auction.

bearsinthesea (author)2008-11-01

Why use a separate resistor for each branch, instead of one for all of them in the circuit coming from the battery?

jeff-o (author)bearsinthesea2008-11-01

The reason is that LEDs don't all have exactly the same voltage drop. When connected in parallel, as the branches are, this could cause problems in the long run. If the difference in voltage drop is large enough, then excess current could be forced through one of the LEDs leading to premature failure.

bearsinthesea (author)jeff-o2008-11-01

I almost understand (noob). Maybe not. You have to know voltage vs current for this, ja?

So, if i had a resistor between the batteries and the power rail to reduce the voltage, most of the current might be hitting one of the LEDs first, even thought all the LEDs light up. And that LED might fail first, because of the current, even though the voltage is ok for it. :/

Because the voltage is the same across all the branches in parallel, but the current adds up for each branch, and could be slightly different for each branch.

Would it be ok if they were all the same LEDs (and therefore the same voltage drop)? I am using all the same FLEDs. (very cheap from china, good tip there).

No, I don't get it. Please tell me where I'm wrong here:
With a resistor after the battery, the current is reduced to a low level, so it can't damage any LEDs, even though the voltage drop will still be the same for every branch (6V). Because resistors limit current.

Maybe i need a different voltage/current for dummies link than the ones i am reading...

Thanks for the help, this is a cool project, and I don't want an LED to burn out early.

jeff-o (author)bearsinthesea2008-11-01

You've almost got it. It's true, each branch will drop 6V from the end of the resistor to the end of the second LED. It's also true, that the currents in each branch will be different from each other, and will all add together.

The resistor is there to absorb (or drop) some of the voltage going through each branch, according to V=IR. So, if each LED should be consuming 2.5V (total 5V) at 20mA, then the resistor must drop the remaining 1V. Using the equation I listed, the value of the resistor must be 50 ohms.

Now, note where I wrote "should be." In reality, unless you measure the voltage drop of each LED and group them together, you never really know how much the voltage drop could be. It could range from 2.5V to 3.1V, for instance. So, the resistor could be anywhere from 50 ohms to 1 ohm. We just pick a value that will work with the average voltage drop we're expecting to see from the LEDs.

The trouble comes when you hook up the LEDs in parallel. LEDs are not resistors, they behave differently. What happens if one LED drops 2.5V, while the other drops 3.1? The LED with the highest voltage drop determines what the drop along the entire parallel chain will be. So, the 2.5V LED is actually being fed 3.1V, which is too much for it to handle. It burns bright for a while, then dies.

A resistor for each parallel LED ensures that each LED gets only the voltage it needs, with the rest being sopped up by the resistor.

yourtubemeera (author)2008-07-16

hey u could keep it upside down for the right effect

Sir-Jackington (author)2008-05-29

Thats pretty cool and I do believe I may put your Instructable to good use and make one or two maybe even three

jeff-o (author)Sir-Jackington2008-05-30

Cool. They go together pretty quick. Try using different shaped jars!

J-Five (author)2008-05-29

One word GROOVY!!!

crippledeath (author)2008-05-27

great job im going to make my own now you have my vote check out my site thank you just click on the link

GorillazMiko (author)2008-05-19

LOL at the baby. Nice job, you definitely got a 5/5 star rating and my vote.

Oh wait, nevermind, you can't vote yet...

I'll remember though!

Patrik (author)2008-05-19

Ooh - purty! :-) Sort of a souped-up version of the LED Mood Jar.

For anyone trying to replicate this: note that the PCB board or perfboard is kinda optional here. You could just solder all the terminals together instead. For example, solder all the + terminals to a common + wire running the circumference of the lid, and gather all the - terminals to a wire at the bottom of the jar, leading back up to the battery.

jeff-o (author)Patrik2008-05-19

Yep, the LED Disco Light in a Jar was inspired by the LED Mood Jar and a few other LED-in-jar instructables here. I suppose you could try it that way, but then you'd have to figure out a different way of securing the battery holder so it doesn't rattle around in there. The PC board provides a nice sturdy surface to attach everything.

Patrik (author)jeff-o2008-05-19

Yeah, rattle-proofing would definitely be a more important design criterion - especially in the hands of little ones. I would probably just hot glue the battery holder to the lid, moving the switch to the side a bit. Do the LEDs rattle around much? There's no worry about the LEDs themselves breaking, of course, but prolonged movement might weaken the solder joints. I guess you could always wrap a little elastic band around the LED strands + battery holder.

jeff-o (author)Patrik2008-05-19

The LEDs don't move much once they're in the jar, there isn't much room between the battery holder and the glass. A dab of hot glue at the base of each branch would probably do the trick if the jar were much larger, with more room to spare.

mspark400 (author)2008-05-19

splendid! good job!! vote and rating for you!! horay!!

exita (author)2008-05-19

Dude, Your kid is so cute :-)

jeff-o (author)exita2008-05-19

Thanks. :D

fungus amungus (author)2008-05-19

You should upload those videos to youtube or google video and embed them. A lot more people will see them that way.

jeff-o (author)fungus amungus2008-05-19

I'll have to get a Youtube account... :)

pacey_waring (author)2008-05-19

can you clarify the purpose of the standoffs?

jeff-o (author)pacey_waring2008-05-19

Done! See step 7 for a bit more clarification.

About This Instructable




Bio: By day, Jeff is the Jack of All Robots at Clearpath Robotics. By night, a mad scientist / hacker / artist / industrial designer wannabe!
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