On Wed, May 30, 2007 12:24 am, Christoph Maier wrote: > On Tue, 2007-05-29 at 23:46 -0700, Gus Wirth wrote: >> Lan Barnes wrote: >> > I need a low volt (0.9 V) way low amp LED for a science project. Radio >> > Shack is hopeless. >> > >> > Can anyone remind me of that great hole-in-the-wall components store's >> > name or address? >> >> >> There is no such thing as an LED that operates in the visible spectrum >> at a voltage less than about 1.2 volts. The lowest voltage LED's are red >> (680 nm wavelength) and the voltage climbs as you move up in spectrum. A >> blue LED (470 nm wavelength) needs about 3.8 volts to work. >> >> Typical currents are about 10-20 milliamps for decent visibility on >> standard brightness LED's. >> >> I have a whole bunch of red and green LED's in my parts box. You're >> welcome to have a few to play with. >> >> If you are really limited in the voltage, it might be possible to build >> a small inverter to step the voltage up. There used to be a great part >> called an LM3909 <http://home.cogeco.ca/~rpaisley4/LM3909.html> that >> worked as a voltage pump to flash an LED but they don't make them any >> more. You could probably build something out of either a germanium >> transistor (0.2 volts saturation) or maybe a specialty FET. I would do >> it as a simple transformer coupled oscillator. Of course the efficiency >> loss would probably kill your current consumption budget. >> >> Gus > > Newer LEDs are surprisingly bright at low currents. > The forward voltage, however, is a hard limit. > > By sheer coincidence, I used a circuit to get enough voltage for a green > LED from only 700mV as proof-of-concept for wine: > http://www.kernel-panic.org/Members/cmaier/hamburger-lugnut-log/archive/2007/02/04/both-linuxes-emulate-windows-xp/ > (by the way, Plone still doesn't work quite right, *&[EMAIL PROTECTED]) > but you'd need an AC waveform for the charge pumps to work. > It's not easy at all to build a DC to AC converter that works from > 700mV. > > HTH > Christoph > >
Hmm ... maybe the red LEDs from my parts box would work ... nope, can't risk it. I tested them on a 1.6 AA battery with no joy. Time is short. <shudder> Fry's it is. -- Lan Barnes SCM Analyst Linux Guy Tcl/Tk Enthusiast Biodiesel Brewer -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
