Simplified Firefly Jar




This is my first instructable so be kind please. Please also keep in mind I'm not an electronics expert. I know just enough to not know what I'm doing.

I was inspired by photozz Fireflies - Analog version. I had two 555 timers but didn't have the cd4026b IC. Instead what I had was a sn7447an IC. Even with the help of photozz I still couldn't get it to work. So I started looking for a different way. I found the simplesit LED blinking circuit on (note: any metteral taken from the above site is copyrighted to Dick Cappel) From there thru trial and error I designed my simplified Fireflies in a jar circuit. We will keep it simple and only do three LED's for now. Ime working on a 10 LED jar.

Parts list.
3 2N3904 NPN Transistors (Almost any other NPN or PNP from your junk box will work)
3 various resistors (I used 2-10K and a 1-1K resistor try different combos from the junk box)
3 100 ohm resisters (this one is a must or you MIGHT blow your LED's)
3 various capasters ( used 1-2200 UF 2-470 UF one 35V and one 16V try different combos.)
3 green surface mount LED (or any other color or kind)
1 Power supply of some sort. I used a Nokia Type ACP-7U. Out put is 3.7V DC at 340 mA I'm to cheap to buy batteries, and the cell phone for this charger became a dogs chew toy.
Various wires. the thiner the better.
1 mason jar. or some other type of inclouser.

Solder gun

Optional but nice.
Universal Breadboard.
Prototype board.

Step 1: The Simple Cuircuit

When using the transistor only use the
emitter and collector. cut the base off or just bend it out of your way.

I will do a little cut and paste from the site I got the circuit from for those that are interested in why and how it works.

In this implementation, a common NPN transistor is used. In the circuit, a 1k resistor charged the 330 uf capacitor until the voltage became large enough to get the emitter-base junction to conduct. In the oscilloscope image, it can be seen that the peak voltage (yellow trace) was a little bit less than 9 volts. At this point transistor turned on quickly and partially discharged the 330 uf capacitor through the LED and the 100 Ohm current limiting resistor. The current wavform, which is the voltage drop across the 100 Ohm resistor, is shown in the blue trace on the scope image. Peak current was 26 milliamps, and the transistor continued to discharge the capacitor until conduction suddenly ceased at 60 milliamps. After the transistor stopped conducting, the capacitor began charging again, thus starting a new cycle.

To see oscilloscope image go to Simplest LED Flasher Circuit

What I did is no rocket science I used a common positive and a common negative and added more transistors. I also mixed and matched different combinations of resistors and capacitors so each LED blinks different then the others. In my mind the best blink fade in fade out combo is a 10K with a 2200 UF capacitor. it only blinks about once every three seconds but it looks more like a real firefly.

The image on this step is copyrighted by Richard Cappels at , and is republished here with permission on this web page.

Step 2: Final Thoughts.

Sorry about the lack of pictures my camera is on the blink. As soon as I get some pictures I will post them.

I used a old mason jar and some very small gage wire to hang the surface mount LED's from. the circuit Is on a perfboard and hot glued in the top the over all effect is awesome except for the power supply wire running into the top. It will be replaced soon with a 2 small 3 volt batteries so the whole unit will be self contained. in addition to the batters it will also be getting a light sensing circuit to turn it on at dusk and off at dawn. I'm even going to put in a small cell phone vibrator to give the appearance of movement.

Remeber this is my first Instructable please be kind. I baleave Ive given credit to every one else work but if Ive forgot anybody please feel free to politely point it out to me and I will correct it.



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    13 Discussions


    7 years ago on Step 2

    I am confused.
    I built this circuit to your specifications and to the original designs specs.
    The LED (3v Amber) lights up to a dim glow and stays on at 12 volts and does nothing entirely at 3 to 11. I tried reversing the 2n3904s collector and emitter and the circuit doesn't function at all.
    Any thoughts?


    9 years ago on Step 2

    sorry, but you camera was dying in early 2007, and now its 2010! where are those upadated photos?

    also, this is a coment bump

    giving 4 stars

    1 reply

    Reply 9 years ago on Step 2

    Well thanks for the bump but that project has sense been torn down and the pieces es used in other experiments.  I had so much fun doing it I might do it again and now I do have a good camera so if I do it again The picks will be there


    12 years ago on Introduction

    Thanks for sharing this idea, i try make my own, i think that simple circuit will work like a Photovore but with a little eolic supply, obviously no with Solar panel supply, with this hack we only put the jar on window open and work in the night with the wind. Romantic idea, ha? :-)

    1 reply

    9 years ago on Step 2

    wow, it's realy simple(the circuit), isn't it dangerous for the transistor? I'm trying to repair led flashing lights(the ones used in construction), the plan s to put another thansistor where you put the led(my leds uses 12 v and 2 amps at all) thanks


    11 years ago on Step 2

    Interesting Instructable, though you may wish to run it through a Spell Checker, some of the spelling was not so great

    Dick Cappels

    11 years ago on Introduction

    One fellow who tried to build the basic flasher circuit had problems because he tried to run it from a 9 volt transistor radio battery. I just put one together using a 2N4401 and found that with a 1k resistor, it operated from 9.1 volts to 20.7 volts. A bit higher than you should expect from a 9 volt batter. Using a 2k resistor raised the upper voltage past the 27 volt maximum output from my bench supply. I appreciate the reference to my web page. Note that my copyrighted material remains my property, even though it is posted on this site.

    1 reply
    DannosDick Cappels

    Reply 11 years ago on Introduction

    Wow thanks for commenting on my little project. I am on your site all the time. You have no idea how much I have learned from your site. you should post some instructables


    12 years ago on Introduction

    Just a little side note here. If you have a well stocked junk box the cost of this project can be 0