Ridiculously low power LED flasher for science day

Get an el-cheapo (tm) volt-ohm meter from Radio Shack. Put on the lowest DC volts range, you should get some action from the needle when you run the 'generator'.

Luhan

Any idea what the open-circuit voltage will be like? I'd expect the source impedance to be low, so there may be lots of current available but maybe not enough voltage to drive an led directly.

If you wind a reasonable coil and drop a super-magnet through it, it will flash an led directly, pretty bright. Also fun: drop a magnet down the bore of a copper water pipe.

John

Hello Stephen,

Supercaps or gold caps. Get one that is rated for high currents (not for mamory backup). Around $2-3 a pop at the mail order places. However, you might have to boost your voltage a bit.

For flashing you can use a simple 74HC14 oscillator. Add a resistor in series with a diode over the feedback for asymmetrical duty cycle, to allow short flashes. I just had to do that and found that the human eye, my eyes at least, can discern 5-10msec flashes at 1/2 sec intervals quite well.

--
Regards, Joerg

http://www.analogconsultants.com

Google "Thomas Scarborough" - he's published loads of stuff on this sort of theme.

If you can find one, (in Australia, I think that Jaycar sell them), an LM3909 LED flasher IC may be what you need. It will brightly flash a LED regularly from a 1.5V or slightly lower supply, by using an internal charge-pump voltage doubler. A Google search will turn up heaps of results, including the datasheet at:-

... Humphrey

As an afterthought, if I were you I would first build one of these generators, then measure it's output into a small load, to check the viability of the idea. If the output is too low, you might not be able to power any kind of LED flasher without spinning the coil fairly fast. ... Humphrey

I gave up on that type of generator and made this one instead. It's VERY simple, yet it directly produces enough output to light an incandescent bulb.

ULTRA-SIMPLE GENERATOR

Any flasher circuit will involve charging a capacitor. So first see if your "generator" can produce enough voltage for success: hook a

1000uF capacitor and a meter across the generator, spin it, and see what voltage you get. If it's below a volt, flasher circuits won't work.

I wonder if a step-up transformer, a diode, and a capacitor would get you enough voltage?

((((((((((((((((((((((( ( ( (o) ) ) ))))))))))))))))))))))) William J. Beaty Research Engineer snipped-for-privacy@chem.washington.edu UW Chem Dept, Bagley Hall RM74 snipped-for-privacy@eskimo.com Box 351700, Seattle, WA 98195-1700 ph425-222-5066 http//staff.washington.edu/wbeaty/

I don't know if something similar exist in the UK, but you might want to check the "dollar stores" (where every thing is a dollar or less) for electronic gizmos to work with. I've found clear balls with flashing LEDs inside that would provide a cheap and quick LED setup. They also have toys and gizmos that have small electric motors that can also be used as generators. They have LCD watches that can be powered by a "potato battery" and toy cell phones that have speech chips in them.

In the UK, the QD chain of stores have LED keychains. They started at £1.99p then dropped to 99p - last time I looked they were charging the lower price as well as offering buy one get one free!

Hello Bill,

What if someone cranks it too hard and the cardboard catches fire?

:-)))

Careful with that if the circuit is not loaded. As a kid I blew up more than one electrolytic with an old phone crank because the voltage kept running up.

You can get stuff going below 1V. That's why I kept lots of Ge transistors.

--
Regards, Joerg

http://www.analogconsultants.com