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  1. #1

    Default Project Lamplighter - my homemade LED keychain fob


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    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; 11-17-2015 at 12:26 PM.

  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
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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.)

  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 09:02 AM.

  9. #9

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post
    What flashlight is that on your keys?

  10. #10

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by dongdong View Post
    What flashlight is that on your keys?
    That's a Peak Eiger AAA in stainless steel.

  11. #11
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Yes, it looks fantastic !
    ... is the archimedes peak

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

    That looks great! I'm interested to know more about the latest setup
    I'm Ryan.

  13. #13

    Default Re: Project Lamplighter - my homemade LED keychain fob

    nice. a copper one of those with that warm glow would be awesome!

  14. #14

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Thanks for all the interest guys! It's super busy in my household and my updates might be a little slow so bear with me.

    The LED is a 2x1mm SMD suspended on tiny wires inside 8mm glass tubing. I temporarily abandoned the Pyrex tubing since it was too hard to cut and switched to laboratory "soft glass". I've done all I can to harden the glass and it's caged on all sides by metal so we'll see how durable it is. I've dropped my keys a couple times with no problem but testing will continue.

    The circuit draws 35μA from 4x LR41 cells. It could be much more efficient, longer running and cheaper if I switched to LR44's but I don't like their larger diameter. The fob is exactly as wide as I want it to be right now so I'm willing to buy $4 worth of cells every 6 months.


    The LED's glass chamber is capped on both ends by white plastic which helps reflect the light and does a great job lighting the entire window. At night on my bedside table it glows like a tiny campfire and I really enjoy the look.


    There are a few things on my To-Do list for the next one:
    • Increase internal battery chamber diameter slightly
    • Aquarium caulking on both ends of the window to help seal against water/dust
    • Reinforce wires so they don't buckle under the stress of assembly
    • Destructive testing (read: throwing this thing at my driveway over and over) to see how sturdy the glass window is

    I'm really excited about having a working prototype and it makes me very proud to see it hanging from the ignition when I'm driving home in the dark. I hope to have a 2nd one built soon for testing and then I hope to make a few for anyone on here who would be interested.

    Stay tuned!

  15. #15

    Default Re: Project Lamplighter - my homemade LED keychain fob

    I like the 'caged' look, very unique.

  16. #16

    Default Re: Project Lamplighter - my homemade LED keychain fob

    That is so awesome and what a marvel of engineering!
    I also agree with you on thinner being worth the couple bucks a year =)

    I know it would require some additional engineering but maybe you could offer different sizes for different batteries?

    Also - have you thought about burying the SMD in Norland61? That would take care of sturdiness issues!
    EDC: MilkySpit 1000-lumen Tri-MC-E L5
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  17. #17

    Default Re: Project Lamplighter - my homemade LED keychain fob

    I WANT ONE or MORE. Great work man keep after it I agree with above post on the Copper also.
    Using Tapatalk

  18. #18
    Flashaholic* sassaquin's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    That is wicked cool.
    And yes, I am interested in purchasing one.
    " The bitterness of poor quality remains long after the sweetness of low price is forgotten." -Ben Franklin

  19. #19
    Flashaholic* KuanR's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    I'm definitely interested and this will be worn around my neck! Please put me down for one
    I'm Ryan.

  20. #20
    Flashaholic* Icarus's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Can you post a close-up of the LED please?

    I like that it is made from brass!
    Last edited by Icarus; 03-04-2015 at 04:42 AM.

  21. #21

    Default Re: Project Lamplighter - my homemade LED keychain fob

    I want one !
    90+ CRI Rules!
    WTB Solarforce Parts,---> Here
    !

  22. #22

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by mcbrat View Post
    nice. a copper one of those with that warm glow would be awesome!
    C101 copper almost tore my old lathe apart. I haven't tried it on the new one but that experience scared me enough to have a healthy respect for it. May give a shot in the future but not right now. I have been working in bronze though! Little redder than brass and looks better than copper when tarnished.


    Quote Originally Posted by mcmc View Post
    Also - have you thought about burying the SMD in Norland61?
    Filling the glass tube with Norland would probably cost a couple hundred dollars! It does a great job securing things in tiny spaces but it's not economical to use in large quantities. As for potting just the emitter in epoxy, it's not really needed as the solder holds it plenty tight. The wires are my problem - keeping them taut is a challenge.

    Quote Originally Posted by Icarus View Post
    Can you post a close-up of the LED please?
    Please disregard the curly wire - one of them snapped loose during final installation and I have no way to fix it on this prototype.


    Last edited by calipsoii; 03-04-2015 at 09:05 PM.

  23. #23
    Flashaholic* Icarus's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post
    As for potting just the emitter in epoxy, it's not really needed as the solder holds it plenty tight. The wires are my problem - keeping them taut is a challenge.



    Please disregard the curly wire - one of them snapped loose during final installation and I have no way to fix it on this prototype.


    Thank you very much for posting those pictures! They are very good!

    As for the wires to the LED, I see that both wires are going to the top of the tube. It might be easier to keep the wires straight and holding the LED in place when you add a thin brass disk at the top and bottom of the glass tube and run/solder the wires from the LED through a hole in the center of the brass disk.

  24. #24

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by Icarus View Post
    solder the wires from the LED through a hole in the center of the brass disk.
    No can do my friend, the wires are carrying the current to the LED. Soldering them to a disk would cause an electrical short which is why I'm using white Delrin. A think a bit of tape or some caulking would do the trick though!

  25. #25
    Flashaholic* Icarus's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Supposing the brass housing is connected to the - of the batteries, the bottom brass disk could be connected to the - of the LED and make contact with the bottom of the lantern. The top brass disk connected to the + of the LED could have a brass nippel to make contact with the + of the battery. I don't know how the lantern looks inside but if necessary a delrin disk + brass nippel could be used as the top disk of the glass tube. Then there is no risk for an electrical short.

  26. #26
    nfetterly's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Add me to your list. I subscribed to the thread a few days ago. Love bronze, have 2 watches made from bronze.


  27. #27

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by calipsoii View Post
    No can do my friend, the wires are carrying the current to the LED. Soldering them to a disk would cause an electrical short which is why I'm using white Delrin. A think a bit of tape or some caulking would do the trick though!
    Why not look at a varnish finish to the wire to stop any shorts?!

  28. #28

    Default Re: Project Lamplighter - my homemade LED keychain fob

    Man these are really awesome. Hope you will be releasing before too long.
    Using Tapatalk

  29. #29
    Flashaholic* Nitroz's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Encapsulating that in clear resin or epoxy would be nice, and would add protection to the wires and the LED.

    Put me on the list for a brass.

  30. #30
    *Flashaholic* Illum's Avatar
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    Default Re: Project Lamplighter - my homemade LED keychain fob

    Quote Originally Posted by Nitroz View Post
    Encapsulating that in clear resin or epoxy would be nice, and would add protection to the wires and the LED.

    Put me on the list for a brass.
    one possible problem with that is that as resin cures it produces quite a bit of heat. Whats the word of that wreaking havoc on an SMT LED?

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