-=> ROY J. TELLASON wrote to WAYNE CHIRNSIDE <=-

 RJT> Yes,  I think perhaps my earlier attempt at messing with those (or
 RJT> maybe it was 4016s) went poorly because I didn't bias them,  or run
 RJT> them off a split supply.
 RJT>  I've got a little circuit here that's a charge pump to give you a
 RJT> little bit of -5V from a +5V supply -- I'll bet that would do the trick
 RJT> and if I feed it unregulated voltage then I could probably have pretty
 RJT> stable dual 5V supplies, which should be more than adequate for
 RJT> line-level audio signals.

 RJT> I wasn't thinking of switching in bunches of different resistors to do
 RJT> gain control,  but rather some sort of pulse-width modulation.  Just
 RJT> gotta pick a high enough frequency and figure out what sort of
 RJT> filtering needs to be at the output end of things to make this work.

Sounds like you might be attempting some sort of single bit
power amplifier?

 WC> Wish I had the circuit for a negative resistance pulser by Forrest
 WC> Mims I once had from Popular Electronics.

 RJT> He sure published an awful lot of stuff.  And much of it is in those
 RJT> little books that you can get at radio shack,  maybe that circuit is in
 RJT> there?

 Perhaps I'll look.

 WC> Would like to pulse some white LEDs I've got now.

 RJT> I have yet to get a hold of any of those,  or any blue ones.

No blue ones here either yet but the packaging is the same for
both types so it tells you the cell types for both.
I don't see myself replacing individual cells when the
whole package is cheaper.

 WC> White LEDs are available from the local Radio Shack for 4.95 each

 RJT> That's a pretty hefty price,  and I don't remember seeing them there,
 RJT> but that's no surprise as I haven't spent that much time in there in
 RJT> recent years anyhow,  and they typically charge more than most places
 RJT> for some stuff.

 I haven't been there in years either but checked the web site to
 find the info.
 I'd expect you could buy a bunch cheaper mail order at someplace
 like DigiKey or Matt Electronics.

 I've both PDF catalogs here and DigiKey's is a bear to read
 but Matt Electronics is easy.

 WC> or you can get the same thing in a battery operated keychain light
 WC> at Walgreens for 1.50 along with 2 3 volt lithium 2016 coin cells.

 RJT> Too bad we don't have any of those around here.

 Perhaps they can be found in some other discount or drugstore.
 Found mine as an impulse buy item right at the checkout.

 WC> The white LED has full length leads with the typical anode longer
 WC> arrangement, the white ones have the 2 2016 cells which fit my
 WC> watch and the blue ones have 1 2032 which fits my computer CMOS
 WC> cell holders :-)

 RJT> Do the white ones take more voltage to operate,  then?

Radio Shack lists theirs at 3.6 volts and I suspect they're identical,
same package style anyway, 20 MA. Max.

I'm guessing given the monochromatic nature of LEDs that the
white LED is actually an ultra-violet LED illuminating
a phospher much like UV illuminates a phospher in a flourescent.
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