From: John Larkin
Subject: Re: Piezo Ignitor to power an LED -- any ideas?
Date: Thu, 21 Nov 2002 08:39:26 -0800
Organization: Posted via Supernews, http://www.supernews.com
X-Newsreader: Forte Agent 1.91/32.564
On Thu, 21 Nov 2002 04:17:16 -0800, J81 wrote:
>I've got this half-baked idea to use a piezo ignitor to power an LED
>which needs 2.5v at around 15ma to 20ma. I'm currently under the
>impression that my piezo ignitor and piezo ignitors in general put out
>micro-amperes of power, at around ten thousand volts or more. I'm
>wondering if it's possible to step down the voltage to 2.5v to briefly
>power my LED, or possibly charge a capacitor which will power the LED
>over a short period of time. If it is possible, how would I go about
>I believe a running shoe was manufactured at some point that had
>little flashing LEDs which were powered by a piezo ignition like I'm
>speaking of, but I can't for the life of me remember who made them.
>Thanks in advance for any help.
Rough numbers: an auto spark plug dumps a few 10's of millijoules of
energy, so I'd guess a piezo would be very roughly in the 10 mJ range.
That would be plenty of energy to flash an LED; after all, it's plenty
to make a visible flash from the spark itself.
So there's enough energy; the problem is impedance matching. You'd
probably need a small stepdown transformer, a small/fast bridge
rectifier (the discharge into the xfmr will probably be oscillatory)
and maybe an output capacitor to stretch the flash width.
You could try using a trigger transformer from a disposable camera
(run in reverse, natch) as the stepdown, and a bridge rectifier made
of 1N914 types. An even higher ratio transformer would be better.