joule thief useful as LED tester

Discussion in 'General Electronics Chat' started by takao21203, Jan 7, 2015.

  1. takao21203

    Thread Starter Distinguished Member

    Apr 28, 2012
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    I used it today for small 0805 LEDs- the piece of paper inside got lost which shows the color.

    With this circuit, you only need to touch one pole from the coil and hold the LED- it lights up!

    Its also faster for other LEDs, handling 1000s of them some always go astray and over time they accumulate.

    DSC02730.jpg

    the transistor doesnt burn out but so far I've been afraid to test with two batteries.
    For larger brightness, and to be able to light up even green neon lamps.

    Or the coil needs more research. i want to try a smaller one with fine wire, and a larger 10mH coil with more turns.

    The board was sitting around for weeks, it drains zero power when off, start with pushbutton, turning off by touching the two coil poles with a finger (the voltage doesnt produce any sensation).

    Maybe its limited by the 2n3906? But it must be more than 60 volts. High voltage transistors have such low hFE that they dont do well for these circuits.
     
    Dr.killjoy likes this.
  2. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    I can't really help out but I think this is a pretty cool project and will come in very handy.. But Keep it going with the research and see what happens lol...




    LOL
    I will be watching lol
    Jay Sr
     
  3. takao21203

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    Apr 28, 2012
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    a groundbreaking revolution for the LED tester market, within 2 years, gaining control of worldwide markets. Its a multi billion dollar industry.
     
  4. takao21203

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    Apr 28, 2012
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    I tried today with two batteries. Pressing the button which shorts the base, the transistor heats up fast (noticeable when holding it).

    Its possible to light up green neon lamps! And the transistor doesnt overheat. There's no load accross the transistor.

    DSC03561.jpg
     
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  5. joeyd999

    AAC Fanatic!

    Jun 6, 2011
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    Your schematic looks like a blocking oscillator to me. Why do you call it a joule thief?
     
  6. takao21203

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    It is in fact a blocking oscillator or at least, similar to these kind of circuits.

    It also has things in common with a Tesla coil circuit- the primary winding is 8 turns only, and the secondary is left open on one end. There are circuits like that or very similar, called "Skinner Exciter".

    Joule Thief is on wikipedia- its a very similar circuit.

    Differences:

    -Push button used for starting
    -No resistor
    -Turns ratio is reversed
    -Secondary left open on one end
    -Loading can happen on primary side (accross transistor), or on secondary side: accross secondary (high voltage), or light up a LED touching only one pole from the secondary winding (the original inductor winding actually).
    -Its PNP technology
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    For testing LEDs, what is wrong with a 9V battery and a 470Ω resistor?
     
  8. takao21203

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    Apr 28, 2012
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    Read the post again line by line? Slowly? Aided with a magniying glass and a dictionary?

    Come on. I clearly wrote I had to deal with 0805 LEDs. And preferably, not solder them, well not just preferably.

    As well I wrote, I can test them by holding them on one end, which is faster than connecting them, if you have a handful of clear LEDs.

    And why a 470R resistor? You can use depleted 9v batteries. In fact, I also use these for testing.

    For the 0805 LEDs it was more handy to just touch it on one end.

    Answer: Handling reasons. OK with you?
     
  9. MikeML

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    If I really, really had to test a bunch of 0805 LEDs, I would use plastic tweezers with copper foil inside the jaws. That is how I test 0805 anythings...
     
  10. joeyd999

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    So...which joules are you thieving?
     
  11. takao21203

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    I havent invented the expression.

    Joules from a dead battery which has no regular use anymore.
     
  12. takao21203

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    I only had to test one from the tape. One had a marking. And the remaining one...well guess.

    I sold LED kits, and handled 10000s of LEDs, so after a while, a few would always end up outside their bags. Have to clear them out time by time, and touching on one pin only is absolutely fast.

    Its highly efficient and time saving. It can serve as small lamp too (with the new 2 batteries, the white LED is very bright).

    It can light up all kinds of neon lamps now.
     
  13. joeyd999

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    Wow, I just learned something today.

    I've never researched a joule thief before....I just assumed it was a circuit that scavenged energy from non-typical sources like vibration, excess heat, etc.

    And now I discovered, via takao and wiki, that it is nothing more than a simple blocking oscillator, the same circuit that I've been building and using repeatedly for the last 25 years or so.

    In fact, I recently posted this thread, which is a high-tech replacement for *my* 2KV from 2 'AA' batteries joule thief.
     
  14. takao21203

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    I'm just lazy, the turns ratio is set, using a Panasonic inductor, adding 8 turns wire to it.

    I've tested with RF inductor but it isnt as easy. There's a gap from the epoxy.
     
  15. ian field

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    Oct 27, 2012
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    Not so much fun, a PP3 isn't cheap and a PP3 doesn't last long even doing only that!
     
  16. ian field

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    See if you can scrounge some used disposable camera carcases from the camera shop - most types run off a single AA battery and charge the photoflash capacitor to a couple or few hundred volts.

    Usually they return the HV secondary to the transistor base so the charging pulses enhance the base drive, this means they have to turn the diode round so the HV is negative WRT the transistor emitter - but you can always rebuild it with a PNP transistor if that's a problem.

    Because the charging current is added into the feedback, it charges rapidly when the capacitor is low charged, it cuts back to just idling when the cap is full.
     
  17. takao21203

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    Apr 28, 2012
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    The days of these camera shops are gone its all digital here. OK I still see them sometimes (single use cameras), but they have become a speciality.

    I wonder if hobbyists on bounty for these shells have ever been really successful or if it is more of an urban myth- the staff neither allowed to stockpile them or to hand them out. That said, analogue photography has almost disappeared- about a decade ago, it still existed. And so the places where you could drop off film rolls for development.

    2)

    I dont plan electrocution, just light up a LED or a neon. Next thing, maybe a Xenon flasher? I have the trigger transformers.
     
  18. takao21203

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    The carbon kinds are cheap. I have to use them for my DMM, and they dont last long. But long enough its not worth it to stepup the voltage (the DMM isnt happy with 5 or 6 volts particulary).
     
  19. #12

    Expert

    Nov 30, 2010
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    Congratulations. That's practically my signature line. :D

    But seriously, I have a Joule Thief flashlight in my pocket because it uses a single AA battery and is sufficient for my needs. Besides that, it can suck a AA battery down below 0.6 volts. :eek:
     
  20. ian field

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    Somewhere I have a big taut-band suspension meter about the same size as an AVO8 - when the 30V high Ohms range battery became unobtainable, I built a blocking oscillator/inverter that fit in the compartment. It runs off the 1.5V low Ohms battery via a push button.
     
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