Lasersaber strikes again. A joule thief king ?

[d3x0r]

Another interesting feature of this circuit.... when I break the connection to the LEDs, the voltage behaviour is just the same. That is, it seems to start, run and stop at the same voltages, judging by the voltmeter, even when there is "no load" and the LED connection is open. I think that's really weird. Steorn would probably say that this indicates OU performance, since the LED light is evidently coming for free.



(ETA: I went out and bought four more loopsticks yesterday.)

ETA2: the corrected schematic:

to be clear.... "the voltage behavior is the same' across the same time span?  or just the high/low character?

[TinselKoala]

to be clear.... "the voltage behavior is the same' across the same time span?  or just the high/low character?

I mean the high-low behaviour, and the seeming rate of discharge during the "run" phase and after "end" (since there is no load I just am looking at the voltmeter).
I have no solid data on the time span... yet. To log it properly I'll have to rig up an Arduino based timer-logger, or see if I can wire together some other test equipment to get accurate timings.
I think I can get times to the fraction of a millisecond, maybe even microsecond, using Arduino and triggering on the light of the LEDs with a proper sensor. This will take a day or two for me to get it together though.

[TinselKoala]

Here's how to make the coil.

1. Stock loopstick variable inductor. The windings are in series, so it's really just one winding. Note the herringbone-weave winding of the fine Litz wire.

2. Two layers of cloth athletic tape, just to make a surface for the next winding.

3. 20 turns in one layer of #23 magnet wire, secured with a layer of heat-shrink tubing (or epoxy on my first coil).

4. 100 turns of #32 magnet wire, secured with another layer of heat-shrink tubing.

[conradelektro]

(ETA: I went out and bought four more loopsticks yesterday.)

@TinselKoala: what was the original purpose of these "loopstick" coils? It looks like they were used in old radios?

It is interesting that the loopstick coil has two windings?

Greetings, Conrad

P.S.: I found the answer: http://en.wikipedia.org/wiki/Loop_antenna

[TinselKoala]

Yes, the ferrite loopstick antenna can be found in just about every AM radio, and the loopstick variable inductor can certainly be used as an antenna in some cases, as I showed in the "electrosmog harvester". But that's not the primary purpose of the variable inductor type. They are used in antenna tuning / matching circuits in multi-band radios or other places where a variable inductor handling high frequencies is needed. (not UHF, just "HF", ten meters and longer)

The Litz wire winding and the herringbone winding / weaving pattern help with the overall efficiency of the loopstick variable inductor. It's interesting to compare the herringbone pattern with coils that use "caduceus windings". The herringbone has the same kind of crossing angles although at less than 90 degrees.

The little metal clip on one end is made to go through a hole in the chassis and then you have the screwdriver slot in the shaft so the inductor can be precisely tuned. These that I have can be varied from about  1-2 mH to about 9-10 mH.

There are two coil windings but really it's a single coil, the two windings are in strict series and in the same direction, the end of one on the outside goes to the start of the next one on the inside. I don't know why these have two winding groups, perhaps for cooling purposes or to get the herringbone geometry right. They are more complex than they seem at first glance, being very carefully constructed using the fine cotton-covered Litz wire and the herringbone weave.

The antenna article was very informative, thanks for linking it.


ETA: Here's a pretty fancy, modern, loopstick antenna:
http://www.palstar.com/en/la30/

ETA2: You've got me looking now. Here's an interesting thread talking about loopstick variable inductors and crystal sets:
http://theradioboard.com/rb/viewtopic.php?t=3777

http://home.earthlink.net/~kd7tog/Loopsticks/RRCoils.PNG

http://home.earthlink.net/~kd7tog/Loopsticks/MiscCoils.PNG