How to Make a Red LED Torch

iceman (Mike) · #1 21-02-2006, 08:14 AM

Hi all.

Chris Marsh (cjmarsh81) has written a great how-to on making your own red-led torch.

You can read the Article by navigating to the IceInSpace How-To page, or directly by clicking on the link below:

How to Build a Red LED Torch

Thanks to Chris for writing the article!

If you'd like to contribute a review, how-to or other article, please contact me.

iceman (Mike) · #2 21-02-2006, 09:21 AM

Article submitted.

cjmarsh81 · #3 21-02-2006, 09:29 AM

Thanks Iceman.

rmcpb (Rob) · #4 21-02-2006, 10:02 AM

Nice simple article. Well done!!

Thanx

Vermin (Tom) · #5 21-02-2006, 10:24 AM

I was going to say, it's missing a current limiting resistor, till I noticed this footnote: "I use NIMH rechargeable batteries because they are a lower voltage ie 1.2V instead of 1.6V. I do not recommend the use of alkaline batteries as you run the risk of popping the LED.".

If you want to use alkaline batteries, you will have to find a way of putting a 1/4W 47 Ohm resistor in series (in-line) with the LED and batteries.

I actually managed to fit one inside the globe body when I did this a while ago. But from memory it wasn't easy.

Strictly speaking you should have a 15 Ohm 1/4W resistor in the NIMH powered circuit, but in practice leaving it out may just shorten the (considerably long) life of the LED a little bit.

cjmarsh81 · #6 21-02-2006, 11:00 AM

The forward voltage of the LED I used is 2.6V. So with two rechargable batteries it is only running on 2.4V. It is not running at the LED's full brightness, but as it is a 6000mcd LED it doesn't matter much. I use it all the time and it is bright enough for me. Yes ideally it probably should have some limiting resistor in it, just in case the batteries are a tad high in voltage when they come out of the charger. I couldn't fit one in easily, and I found it works fine without it so I didn't bother.

cjmarsh81 · #7 21-02-2006, 11:05 AM

I have a nice little circuit for an oscillator to run the LED on a single battery at full brightness if anyone wants it. Came in one of those DSE kits for a LED Torch. The only problem I have is the LED must be permanently soldered to the circuit or the capacitor builds up a 90V charge and pops the LED when it is reconnected. The problem is getting the switch to work with this circuit.

Vermin (Tom) · #8 21-02-2006, 12:26 PM

Quote:

Originally Posted by cjmarsh81

The forward voltage of the LED I used is 2.6V.

Ah OK, I was assuming it was closer to 2.0V like most red LEDs, sorry. A 15 Ohm would do for alkaline batteries then, and (as you say), none for the NIMH.

I'd be interested in seeing charge pump circuit, shouldn't be too hard to add a switch and maybe do something about the 90V.

BTW, have you seen "the joule thief"? http://www.emanator.demon.co.uk/bigclive/joule.htm

rmcpb (Rob) · #9 21-02-2006, 12:35 PM

Isn't this hobby amazing. We start out with stars in our eyes, get into optics/physics of light, woodworking, metalwork, expansion coefficients of glass, electronics, give quantum physics a go and for a bit of a finisher try to get to grips with the evolution of the universe.

barees63 · #10 21-02-2006, 12:47 PM

Thanks for the article! I have that exact same torch currently covered with red cellophane, I also happen to have the same ultrabright LED sitting in a box of bits so you've given me the prod I needed to do something with it..

cjmarsh81 · #11 21-02-2006, 01:35 PM

Barees. Thats great. It is an easy and very useful little torch now.

Vermin, I hadn't seen that article. It is very interesting and I may give it a go. When I get a chance I will take a photo of the oscillator circuit and post it here. Though this "joule thief" appears to be much simpler and does the same thing.

By the way, if you are after a very bright torch check these LED's out http://cgi.ebay.com.au/NEW-50X-10mm-...QQcmdZViewItem
They probably have a narrow beam but they put my 6000mcd LED to shame.

rmcpb, you are right. I wouldn't have believed some of the topics that come up on this forum and still relate to astronomy.

ving (David) · #12 21-02-2006, 04:36 PM

good stuff

much better than cellophane.

on a side note. there is nothing more anoying than those red headlamps... yeah they are red, but when someone is talking to you and they shine it right in your eyes... BANG! i dont care what colour it is, there goes the night vision

barees63 · #13 21-02-2006, 06:50 PM

I just made mine, I used a 47 ohm resister (I think it should have been slightly bigger since this will run it near its maximum of 30mA? it's a while since I've done much fiddling with electronics).. FWIW, I found it was quite easy to attach the resister to the +ve lead of the LED by cutting the lead short and soldering the resister right up close to the LED it fit easily inside the bulb base. works great - thanks for the inspiration!

cjmarsh81 · #14 21-02-2006, 07:09 PM

Barees, are you running it on Alkalines or rechargables? If it is rechargables you don't really need the resistor. Well done on soldering the 47ohm resistor in, I found it too small and fiddly.

barees63 · #15 21-02-2006, 07:16 PM

I'm using alkalines for now so I thought I should include it..

cjmarsh81 · #16 21-02-2006, 07:22 PM

Yeah good idea, probably would have popped otherwise.

I probably should have mentioned in the article that I chose this torch over other ones I had because of the centre spot. This I have found helps to reflect the light back into the mirror and provide a wider usable area.

circumpolar (Matt) · #17 21-02-2006, 07:35 PM

Just made one.........

Well, I meen 4!

Two for me (you never know when one might die)
and two for the kids!!

The torches from Big W at $1.60 each
LED's were $2.20 each
So I bought four of everything.

sheeny (Al) · #18 21-02-2006, 08:16 PM

What a beauty of a little project!

Good stuff!

Al.

RAJAH235 · #19 21-02-2006, 08:28 PM

Nice job cj.. I never thought about making or submitting an article about them.Well done.

fwiw. Been making & selling these for yrs. I include the resistor inside the flanged holder just in case they get put in some other torch. Easy as pie. I use a 150 or 300 Ohm resistor, with a 1000mcd, 5 mm red LED, as I find most people do not want the LED too bright.
I usually make 10 aat.

L.
ps. hint for those interested. Hold the globe with an old pair of long nose pliers & hold over gas ring for a few seconds, to melt the high temp cement/glue & the solder in the 'positive' hole. The cement can all be scraped out to give a bit more room.
pps. Even made a couple of 'specials' for the "Big Jim", "Dolphin" torches. (reverse polarity of LED tho & increase the resistor to ~470 Ohm).

wavelandscott (Scott) · #20 21-02-2006, 10:18 PM

Nice project...it is amazing how "handy" some peole are...