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Thread: Project Lamplighter - my homemade LED keychain fob

  1. #1

    Default Project Lamplighter - my homemade LED keychain fob

    Introduction

    Hi CPF!

    I suppose a quick introduction is in order. My name's Mike and I'm here at this support group to get help with my flashlight addicti-

    Wait, wrong introduction, let's try that again.

    My name's Mike and I'm a flashlight enthusiast who's been dabbling in hobby electronics lately. The purpose of this thread is to serve as a mini build log for a project I've been working on. So, with that out of the way, let's get down to business!


    The Idea

    When I was 18 and my strange fascination with flashlights was just taking hold, I had the idea to make something that would hang on my keychain and glow. There were plenty of keychain lights on the market at the time, but I didn't want one that would burn bright for a couple hours before it's expensive coin cell battery died. I wanted one that would burn ever so dimly for a very loooooooooooong time. Not a glow-in-the-dark fob either; those required that you charge them up, and there was no way they were going to charge in the dark depths of my pockets.

    No, this had to be something that consumed batteries and glowed weakly. It sounded simple, but after starting the project a dozen times in the last decade, it never really materialized. I eventually stumbled across CPF, and learned such a thing already existed and had been used on watch faces and gun sights for years! You, of course, know what I'm talking about:


    The problem was, this just wasn't the same. It was lacking that... technological... feeling. I wanted to see batteries being converted into photons. It was time to do something about it.


    The Prototype

    In my previous build logs, I've tried hard to take meticulous pictures of the steps involved. To be honest, this project caught me completely off-guard, so I have very few pictures of the actual construction. It started with a whirlwind buying spree of surface mount components and ended hours and hours later with a chunk of protoboard I'd crudely shaped into a rectangle using tin snips. It wasn't pretty, but I'll be damned if it didn't work.


    The problem became the host - what do I put these electronic guts into? As much as I might pine for one, I do not own a metal lathe, nor have I ever even operated one. I imagine the noise of one in full operation is probably somewhere between a Saturn V launch and a car accident, so I don't know how much my neighbours would appreciate me placing one in my backyard.

    A quick trip to Home Depot and I returned with an armload of DIY components. Tubing, copper piping, fittings, brass elbows, you name it. Each was tested for fit on my battery of choice, and each failed miserably. It was during this testing that I slipped a battery into a transparent piece of flexible refrigerator supply hose and it just clicked: it had to be see-through. It just looked too cool not to be. Knowing what I had to find and with a few rough ideas where to find it, it was time to fashion a body.

    I did eventually find my tubing. It's not perfect, but it works, and that's good enough for me.


    The Pictures

    It's funny - part of me is worried that if I post these here, someone will look at them and say "Wow, that looks like a 5th grader made it". The other part of me is so happy to have actually brought a 10 year-old idea to fruition that I don't care. I hope you enjoy them!

    This is the finished product.


    And this is it when you turn the lights out.


    I bought the surface mount LED for this prototype from my local electronics store. Judging by the yellowing cardboard it was attached to, I'd guess it to be as old as I am. It's rated at 9mcd. The order I have in with DigiKey should arrive tomorrow, and each of the four colors range from 150-300mcd. Needless to say, they're going to be a great deal brighter with the the same or better efficiency than this one.



    That said, even this little guy is no slouch, he holds his own against a pair of locators on my favorite lights.


    The size is almost exactly what I imagined it to be.



    To help diffuse the light a little, protect the circuit board from water, and keep lint out, I sealed both ends with hot glue.



    The Specifications

    So now that you've seen the pictures, here's a quick rundown of the specifications:

    Housing
    Clear rigid PVC with some hot glue

    Power Source
    4x LR41 alkaline batteries wired in series. Approximately 30-40mah each. User replaceable.

    Driver
    Homemade constant-current circuit. If my calculations are correct, it's driving the LED at 0.005ma

    Runtime
    This is the big question for me, I simply don't know how long it'll run for. The batteries are driven in series, making them capable of delivering 6V, but they really only need to provide 1.1V to meet the forward voltage of the LED. The circuit is supposed to be a very efficient direct-driven one, so I can't imagine it's worse than 80%. So how long will it run for? I'll tell you when this little guy goes out.



    Conclusion

    That is all I have to share right now, but don't worry, this project isn't done yet. Heck, it's just getting started! The new LED's should arrive tomorrow and hopefully in the next week I'll have some time to construct a few more. Plus, I'll chime in with the runtime when the amber LED glowing dimly on it's protoboard finally goes dark.

    Until then, thanks for reading!

    Cheers,
    - Mike

    p.s. So why the name 'lamplighter'? Well, I pictured this as being very much like the lamplighters of old - using their tiny embers to ignite a much larger light. This is the tiny light that guides me to the much larger light I always have on my keychain.
    Last edited by calipsoii; 10-21-2011 at 08:06 AM.

  2. #2

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Well, I have to say I'm impressed. Kinda reminds me of those "find me" beacons that some larger flashlights have. It's such a simple idea at its core, I love it! Good luck with the build. I think it's great when someone takes an idea and turns it into reality...

    -DF
    KineticParadox ...a personal web space with my CBA Battery Testing and my LED Bin Coding Charts.

  3. #3
    Flashaholic
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Love it. This is way more fun than the 10000x maglite modding threads.

  4. #4
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Great job, very cool looking. Can you provide a schematic for the circuit you made? seems to me at first glance if you used some of the batteries in parallel instead of all series you might get even more run time from them.. then again not knowing the schematic...

  5. #5

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by jason 77 View Post
    Great job, very cool looking. Can you provide a schematic for the circuit you made? seems to me at first glance if you used some of the batteries in parallel instead of all series you might get even more run time from them.. then again not knowing the schematic...
    Thanks! I thought about parallel vs. series wiring but there's not really any room in the current body to run two wires, so ended up just going series. I've no idea what effect that'll have on runtime.

    The circuit is a very simple one with only a couple parts: http://www.instructables.com/id/Powe...stant-current/

  6. #6
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post
    The circuit is a very simple one with only a couple parts: http://www.instructables.com/id/Powe...stant-current/
    HA! that's the one I've used many times, never thought of using SMD parts for it though! So the sense resistor is what like 100 ohms to get such a low CC of .005 mA?

  7. #7

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by jason 77 View Post
    HA! that's the one I've used many times, never thought of using SMD parts for it though! So the sense resistor is what like 100 ohms to get such a low CC of .005 mA?
    I used 100k ohm resistors for both. At first I couldn't even tell if the LED was lit, but it's more than enough light at night.

  8. #8

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post
    As much as I might pine for one, I do not own a metal lathe, nor have I ever even operated one. I imagine the noise of one in full operation is probably somewhere between a Saturn V launch and a car accident, so I don't know how much my neighbours would appreciate me placing one in my backyard.
    I LOL'd.

    4x LR41 alkaline batteries wired in series. Approximately 30-40mah each. User replaceable.
    As you probably already know, Silver-Oxide SR41 cells last longer and don't leak nasty battery acid.

    Driver
    Homemade constant-current circuit.
    I've been looking for a small component-count buck driver (EDIT: NVM, I followed the Instructables link and I see now that it's actually a linear circuit). Still, at such low drive levels, linear might well be more efficient than a switchmode buck!

    p.s. So why the name 'lamplighter'? Well, I pictured this as being very much like the lamplighters of old - using their tiny embers to ignite a much larger light. This is the tiny light that guides me to the much larger light I always have on my keychain.
    This is so awesome. And none of the legal issues surrounding tritium vials. I'm only sorry I didn't think of it first.
    Last edited by tylernt; 10-23-2011 at 08:02 AM.

  9. #9
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Hi Mike:

    That's cool! I love when I can re-purpose something as a housing for a project - probably explains why I can never get out of a hardware store in less than an hour.

    Random thoughts:

    For a locator, particularly a dim one, it might be easier to spot if it's blinking, which could potentially extend run time, too. But that adds complexity to the circuit.

    Have you seen the "Joule Thief" type circuits? http://en.wikipedia.org/wiki/Joule_thief
    (It does use an inductor, but one of the linked articles shows one built into a PR-222 base, so it doesn't have to be too huge.)

  10. #10

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Thanks BobVA!

    I agree that blinking is probably far more noticeable than always-on. Originally I thought it would be cool to have a "breathing" animation like Apple computers do when they're in stand-by. The problem is that every component you add uses power, so I wasn't sure how badly adding a micro would shorten lamp life. Plus I'm still working on protoboard so there was nowhere to fit one in.

    The Joule Thief is another good idea, but I was under the impression that they drain very quickly at high voltages and very slowly at low ones? Everything I've read says that using them with full batteries doesn't have any advantages since they drain them at a normal pace. I was going to try a Joule Thief variation but my local electronics guy just shrugged when I asked him if they had any toroids or inductors.

    On the bright side, my runtime test is just about to hit the 3 week mark, which was my original goal. Everything after this is pretty much gravy.

  11. #11

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post
    The problem is that every component you add uses power, so I wasn't sure how badly adding a micro would shorten lamp life.
    Indeed, it's the great irony of LED circuit design that doing things to save on power consumption typically add more power consumption, for a net loss.

    Microcontrollers do have very low idle current draws, but for months-long runtime on watch batteries, I think we can do better. Perhaps a small capacitor that charges through a resistor over the space of 1-2 seconds, then discharges a strobe through the LED via a transistor or two. That way you're producing light using the same energy you're using to time the flashes. You can even drop the constant-current feature; LED intensity will remain the same but with fresh batteries the strobe will happen more frequently and with weak batteries the strobe will happen less frequently (you could even call this a feature: kind of a battery "gas gauge").

  12. #12
    Flashaholic sunny_nites's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Great build!

    I did something similar for a locator light behind a clear button cover. I used a 3mm LED and sanded two sides almost flat so the lens was diffused into a kind of light pipe. Put out an amazing amount of light for the current draw. I tried it with blue, red, green and orange LEDs. Not sure why but at the same current draw the blue was by far the brightest.

    Something along those lines might boost your light output without using any more current. If there is enough room that is! Looks pretty tight in your case.

    Anyway, great build and thanks for all the pics!
    So many LEDs, so little time...

  13. #13
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by tylernt View Post
    . . . . Perhaps a small capacitor that charges through a resistor over the space of 1-2 seconds, then discharges a strobe through the LED via a transistor or two. That way you're producing light using the same energy you're using to time the flashes. . . . .
    That's what NatSemi designed the LM3909 LED Flasher for.

  14. #14

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by MikeAusC View Post
    That's what NatSemi designed the LM3909 LED Flasher for.
    Heh, well played sir.

    That IC appears to consume 0.5mA though -- fine for an AAA Lamplighter, but for button cells I think we're in the realm of <0.01mA type circuits.

  15. #15
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Here's a schematic I stumbled on that claims an average 6 microamps drain from a 3v supply. It does need a 47 uF cap, though. Probably be able to get the shelf life out of a CR2 with it.

    Low Power Flasher
    Last edited by BobVA; 10-24-2011 at 06:57 PM.

  16. #16
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    Default Dupe deleted

    Mod - please delete
    Last edited by BobVA; 10-24-2011 at 06:57 PM.

  17. #17

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by BobVA View Post
    Here's a schematic I stumbled on that claims an average 6 microamps drain from a 3v supply.
    Impressive!!

  18. #18

    Default Re: Project Lamplighter - my homemade LED keychain fob

    This rocks!!!! Now I know what I might have to do with some of the ZXLD chips I bought... hmmmm... AAAA batteries may have a use after all.

  19. #19

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by BobVA View Post
    Here's a schematic I stumbled on that claims an average 6 microamps drain from a 3v supply. It does need a 47 uF cap, though. Probably be able to get the shelf life out of a CR2 with it.

    Low Power Flasher


    Wow, that's pretty crazy. Definitely going to give that circuit a try when I get a chance. My LED's arrived today and they just so happen to be Kingbright. The author of that isn't joking when he says the green one is bright, not only did it cost 4x as much as the others, it's almost blinding when fully powered. I can't wait to try it out.

  20. #20
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post


    Wow, that's pretty crazy. Definitely going to give that circuit a try when I get a chance. My LED's arrived today and they just so happen to be Kingbright. The author of that isn't joking when he says the green one is bright, not only did it cost 4x as much as the others, it's almost blinding when fully powered. I can't wait to try it out.
    Can you tell me what kind of LEDs you ordered, brand, part #, etc.

  21. #21

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by jason 77 View Post
    Can you tell me what kind of LEDs you ordered, brand, part #, etc.
    Digikey part numbers
    754-1130-1-ND
    754-1133-1-ND
    754-1437-1-ND
    754-1438-1-ND

  22. #22

    Default Re: Project Lamplighter - my homemade LED keychain fob

    You've inspired me. I just got in:

    516-1396-ND
    516-1397-ND

    Both of these have a Vf low enough to not need any circuitry when run off of a 1.5V watch watch battery (379). I need to make myself some new test leads for my Fluke, however as the current is so low, the resistance in my old leads is throwing my readings off. Still as bright or brighter than the tritium vials I have, however.

    -DF
    KineticParadox ...a personal web space with my CBA Battery Testing and my LED Bin Coding Charts.

  23. #23
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post


    Wow, that's pretty crazy. Definitely going to give that circuit a try when I get a chance. ...

    Awesome - Keep us posted and thanks for the feedback on the Kingbright green!

    (I've got the circuit printed out and on my "to do" list, too.)

  24. #24

    Default Re: Project Lamplighter - my homemade LED keychain fob

    great idea! I made one on Sunday (after reading this thread), just a red smd led connected directly to a LR44 (1.5V) button cell battery. it glows! let's see, how long it lasts.



    I want to try this flasher: http://www.discovercircuits.com/DJ-Circuits/OSC4.htm (the one on the right)
    cree q3 + 2" aspheric... that's not a flashlight, that's a f**king laser!!!1!

  25. #25

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by DFiorentino View Post
    You've inspired me. I just got in:

    516-1396-ND
    516-1397-ND

    Both of these have a Vf low enough to not need any circuitry when run off of a 1.5V watch watch battery (379). I need to make myself some new test leads for my Fluke, however as the current is so low, the resistance in my old leads is throwing my readings off. Still as bright or brighter than the tritium vials I have, however.

    -DF
    Nice! I like the idea of those LED's - do you find the long leads off each side make them easier to work with? Can we get some pictures of the final product?

    Quote Originally Posted by 3zuli View Post
    great idea! I made one on Sunday (after reading this thread), just a red smd led connected directly to a LR44 (1.5V) button cell battery. it glows! let's see, how long it lasts.

    I want to try this flasher: http://www.discovercircuits.com/DJ-Circuits/OSC4.htm (the one on the right)
    Looks awesome! Did you find it difficult soldering directly to the battery? I've never tried out of fear of overheating it and having it blow up in my face. The few times I've tried to solder leads to rare-earth magnets has been traumatizing enough...

  26. #26

    Default Re: Project Lamplighter - my homemade LED keychain fob

    No final product yet as I'm just beta testing different parts and ideas. I prefer red myself, so I'll likely won't test any other color possibilities. Here are some quick comparo shots with some tritium vials and some tritium keychain markers. The LED in the upper left is a 516-1311-ND (3mm) and the one to the lower left is a 516-1397-ND. The 1397's leads may be a nice touch or could be a hindrance according to the final host I decide on. I will say they are VERY frail/delicate to handle.

    Pics descending in exposure; starting with 15 seconds...

    #1


    #2


    #3


    #4


    #5


    #6


    #7



    #4 is pretty close to what my eyes see. And this was taken in an almost dark room, save the LED stand-by lighting from my many digital/electronic devices.

    -DF
    KineticParadox ...a personal web space with my CBA Battery Testing and my LED Bin Coding Charts.

  27. #27

    Default Re: Project Lamplighter - my homemade LED keychain fob

    I may try driving 5 or 6 of these LEDs off of a small 9V A32 battery I just got. If I can keep the current low enough, it would make a nice 360 degree keychain marker. Don't know how long it would last though...

    -DF
    KineticParadox ...a personal web space with my CBA Battery Testing and my LED Bin Coding Charts.

  28. #28

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post
    Looks awesome! Did you find it difficult soldering directly to the battery? I've never tried out of fear of overheating it and having it blow up in my face. The few times I've tried to solder leads to rare-earth magnets has been traumatizing enough...
    It's a bit tricky, but pretty simple: just sand the place, where you want to solder and use some soldering paste. I recommend to use 100W soldering iron, because you want it to be able to heat up the entire battery quickly. also, use a vice to hold the battery while soldering, this makes things a lot easier.
    Last edited by 3zuli; 10-26-2011 at 11:36 PM.
    cree q3 + 2" aspheric... that's not a flashlight, that's a f**king laser!!!1!

  29. #29
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    Naughty Re: Project Lamplighter - my homemade LED keychain fob

    Very cool, Calipsoii!!!

    They look very awesome and are so simple(not that I could ever do it :P) and sweet. I would buy one if you ever make more???

  30. #30

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Hi all!

    Well, I'm happy to say that the runtime test continues - it just passed the 1 month mark and shows no signs of stopping.


    I mentioned a while ago that my new LED's arrived, but it took until today to find the free time to sit down and try them out. They're easily a few times brighter than the original red one I made and the green is very eye-catching in the dark.

    I'm trying a new surface treatment that'll hopefully keep the top nice and transparent. Hot glue seems to pick up a ton of lint and scratches and after a couple weeks in your pocket it just doesn't look that good. I'll let you know how this one holds up.

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