Instructables

Single Cell, White LED Torch Fits in a Matchbox

A little while ago, Makezine blog listed two interesting sites: HOW TO - Make a rusty nail LED night light and ELM - AVR based radio spectrum monitor.

Chan has a great site and he has put up a lot of interesting projects, incidentally many of them based on AVR. One of his projects (not based on AVR) is a pocket LED light. He describes a blocking oscillator based single cell, white LED torch. This and rusty nail project got me thinking and I started experimenting with Chan circuit. The circuit is very robust and it worked with a wide variety of transistors; I tried BC547, 2N2222 and 2n3904.

But the real fun and challenge was in building an enclosure for this torch. I have been a big fan of matchboxes; as a kid I used to collect empty matchboxes everywhere I went. I thought the art on matchboxes reflected the local culture.

Long ago, I built a data logger that could fit in a match box (I never completed it in that form, settling to find a much larger enclosure). But now I was determined to fit the white LED torch circuit AND the AA cell in a matchbox.
 
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Step 1: Build the matchbox tray with pieces of PCB

I took a fairly large matchbox and threw away the tray and decided to build my own tray using a technique I had learnt as a radio Ham: to use pieces of PCB and to solder them together to make a faraday cage of any size. I cut three pieces of PCB. I Drilled a large hole to accommodate the 10mm LED in one of the PCBs.

Step 2: Make a cutout for the switch on one of the side walls of the tray

On another PCB, I made a cutout for the On/Off switch as seen here. The body of the switch was bent and soldered to the PCB so that it was secure.

Step 3: Another view of the switch soldered on the PCB

Another view of the switch soldered on the PCB.
BOOJAN3 years ago
daaaamn, nice box, i havent thought about this kind of box for the joule thief...nice instructable mate :D
king20103 years ago
As i am not good in electronic, could any one help me making the coil? whether i need to make 2 coils or the ferrite material will have the terminals? what indicates the 2 "dots" in the circuit diagram.
thulasidas3 years ago
Simple and easy circuit. Please help me to make the coil. What is the name of the "Black part" in which coil is present,
Gadre (author)  thulasidas3 years ago
Its a ferrite former on which the coil is wound. You could use ferrite material in any shape such as a dumb-bell or a toroid.
Good Project.
I could offer this as a kit very soon with a small plastic case like a match box and with all components. I would make one myself soon and post the link with pictures soon.
Thanks and well done
Best Regards
Sunil
http://cqbitx.blogspot.com
imakethings5 years ago
can it work on voltages less than 1.5 volts?
imakethings5 years ago
is it a step up transformer? or a joule thief?
WardXmodem5 years ago
I made one - using one of about 10 toroids I bought - about 1cm diameter; then today I took apart some old equipment to salvage and found a 1" toroid. It didn't work as well. Anyone know if you should interleave the turns, or make them more like a transformer "picture", i.e.. one coil on one side, and one on the other? The larger one worked but drained the battery almost like a short - I'll have to double check my wiring. P.S. I am using one of those multi-socket breadboard things, and made a trick of taping my 4 coil leads as they exit the socket, so I can unplug and replug it (or change to another coil). Cheap plug! haha. I'm going to try "going crazy" with this, I bought a "bag of ferrite beads", from eBay, I hope they are big enough to get the 20-25 turns through.
The ferrite beads I bought are Outer Diam: 0.15"(3.8mm), Inner Diam: 0.059"(1.5mm), and I could only get about 4 turns (each, 8 total) of 30ga. wire, but IT WORKED!!!!!!!! I then, through eBay, bought various sizes, and found I could get about 8 turns (16 total) of #33 wire, and that worked even better. THEN since this is called a "Joule Thief", I decided to make it more of a PUN, namely that a "jewel thief" would only work in the dark. SO I changed the 220 ohm resistor to a 10 turn potentiometer, and saw how far I could go, with a phototransistor pulling it down to ground. A 20K ohm value turned out to be correct, and now a blue LED will only light if the room is quite dark. NOTE I have perverted the original design from a bright flashlight kind of thing, to a smaller "marker" light with extremely long battery life, i.e. in a very darkened room where you might bump into something, you can place one of these like ships use light houses to avoid piers, etc. If someone wishes to write to me as WardXmodem at my Yahoo address, I would be willing to ship a tiny bead and a foot or two of #33 wire, so you could make one. NOTE these are tiny, you need steady hands and good eyes. If you want me to put together "everything" - a transistor, an LED, the coil, and a resistor, let me know, this stuff doesn't cost much at all. I reserve the right to NOT respond to requests should I get overwhelmed or any other good reason.
Gadre (author)  WardXmodem5 years ago
Could you please post pictures of your creation? Thanks,
It is just on a socket board at this time. I'm trying to figure the best thing to "make it into", perhaps a twist-off plastic bottle cap? I also have some "Lumalite" ivory colored casting resin, etc. The toroid is so small and the wires so fine, other than just direct soldering to say transistor leads, I'm trying to figure a way to "mount" it. Perhaps just a tiny dab of hot melt glue on the transistor to hold it in place ;-)
Gadre (author)  WardXmodem5 years ago
Congratulations! Good Job...
hmms6 years ago
take a look at my led torch! the case is made from the packaging bax tht my chamelion ni-mh batteries came in!
P1010133.JPG
microman1717 years ago
for some reason niether of the versions I tried are wokring (ver2: Make A Joule Thief Why is this?? Nex im going to try it on a rusty nail. I even tried tapping it with the cap to make it work but that didnt work. Any Ideas?? I am useing an NPN transistor (BC548)
dude i had the same prob. i suggest u to interchange the connections of the coil . it will surely work!!
Tnaks!! next time im into this ill try it again!
Gadre (author)  microman1717 years ago
The important point is the way the coil is made and connected. I suspect that your coil may not be connected properly.
Are you sure?? I have make 3 coils... The joule thief one the rusty nail one and your one. Thanks for helping me out btw. I found the it outputs 2.4v AC...???
hmms6 years ago
pls tell me where can i get the core of the inductor???
acaz937 years ago
just for curiosity do you know the value of the coil in henries?
stone34087 years ago
Great job! Very simple very effective.
excellent, i saw the rusty nail blocking oscillator and think this is an brilliant extension.
skids9277 years ago
Isn't a battery, resistor switch and bulb a little bit easier? what is the point of the extra coils and stuff? Im not trying to put you down, it turned out nice, I am just curious.
Gadre (author)  skids9277 years ago
The bulb would drain out the battery quite rapidly. A white LED on the other hand lasts longer, but requires a voltage of 3V or slightly more than that for operation. That is where the coil, transistor and resistor come in. These three components make a very simple step-up DC-DC converter which is suitable to drive the white LED.
isn't the coil thing a home made capasiter? (somthing that builds a electric charge? (i think)). Im kinda a new at electronic stuff so could you show a little more detail in the coil, please?
Actually a coil is the so-to-say opposite of a capacitor, while a C stores electric charge and so build up a voltage, a coil stores current and by altering the potential via the Transistor, you set the potential of the upper end of the coil free so that the charged current has to flow through the LED while building up the needed Voltage. You see almost the same concept in engine ignition if the LED would be an Air gap you might even see a tiny little spark. Any given current will theoretically build up a infinite Voltage for a infinite Resistor (Air-Gap) U=R*I. Of course the given circuit isn't made for sparks.

I love the simplicity of the implemented circuit.
Visitor7 years ago
The character encoding you use seems to be broken. There is "garbage" between words "Chan s circuit" and "1.5V cell". Please fix. Thank you.
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