Lasersaber strikes again. A joule thief king ?

[Pirate88179]

That's pretty neat, but also pretty expensive and heavy.

I've been using a "slinky" spring toy thing for an antenna for my Australia Radio crystal set. It works great! And it's 'tunable' by how much you stretch it out.

A slinky?  What a brilliant invention (yet another device that was discovered by accident while attempting to make something else) and also, what a brilliant new use for it.  Tunable too....excellent!  Great thinking over there.

Bill

[Farmhand]

Well the difference in transistors and their drive requirements makes a big difference to running down a cap. I'm working on a single coil circuit to rival the performance of This Super Looper circuit, still not sure where the looper part comes from, But anyway just the difference between the power draw when using an MPSA06 as compared to an MPSA18 is huge in this low power scale. I noticed the MPSA18 transistor doesn't draw down the drive pulse as much as the MPSA06 Could the base of the MPSA18 allow less current to pass and still work well ? And could this be why one transistor gives better efficiency results at lower voltages than another ?

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[TinselKoala]

@Bill: I can't really claim originality for the "slinky antenna" idea. I can't even remember when I first used one for that purpose! But about 15 years ago I made a great electrostatic voltmeter out of a Slinky, taking advantage of the like-charge repulsion effect. Dangle the slinky inside a big transparent plastic tube, with a little weight on the bottom of the spring and connect the HV source to the top. The slinky will stretch more and more as the applied voltage goes up.

@Farmhand:
I tried MPSA18 and it results in a slightly dimmer LED stack, a bit slower discharge rate, but the LEDs go out at a slightly higher voltage than they did with the 2sc3198.

Here's the thing running on a "radio shack" photovoltaic cell:

http://www.youtube.com/watch?v=BHI7LnVWBlY

(I just realized I've had that red MagLite for 30 years.)

[Farmhand]

Time fly's hey, Good job with the loopstick. I am seeing similar results with the MPSA18, the LED gets dimmer as the voltage drops and the lower the voltage drops the less is the power draw, so the lower the voltage goes the longer it runs, takes too long to wait for my 25 Farads to drop under 0.6 volts, it just keeps dropping slower and continues to run.

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[TinselKoala]

You could put a pushbutton and discharge resistor (one or two ohms) across the capacitor. That way you can take it down to whatever voltage you want to be looking at.


I have some interesting transistor data on my SooperLooper low-voltage version of the LaserSaber circuit. As I showed in the last video, the thing starts at a higher voltage just above 0.4 volts and runs down to something around 0.12 volts. That's using the 2sc3198 transistor.

Without making any changes in the circuit or tuning, and using the PV cell and flashlight as the power source, I've tested 4 transistors.

MPSA18 Start: 0.430 V   End: 0.123 V
2sc3198 Start: 0.443 V   End: 0.111 V
BC337-25 Start: 0.409 V   End: 0.104 V

--and the Low Voltage Winner (a real surprise)---

2n2222a Start: 0.420 V  End 0.102 V


I'm defining "end" as the minimum voltage at which I can barely see a glow in all three LEDs, sustained by carefully shining the flashlight partially onto the PV cell.

I think the longest run in terms of time is given by the 2sc3198, probably because of the higher initial charge voltage at Start.


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: