Looking for BIG capacitors.

[Kareem Shehata]

On Thu, 2007-07-05 at 09:38 -0400, James Knott wrote:

> Colin McGregor wrote:
> > Comes back to my on-going love/hate relationship with
> > MythTV (great program but a TOTAL resource PIG!).
> > Anyway what I want is an infrared transciever, so the
> > MythTV box can both understand an IR remote, and can
> > control other IR devices (like cable box, and VCR).
> > The receiver part is painless, there are good, easy to
> > build IR receivers plans available (I wrote about one
> > for linuxjournal.com :-) ), the transmitter is the
> > problem. How do you provide power to light the IR LED?
> > Well, the conventional answers are:
> >
> > - You don't really, basically you just put in an IR
> > LED and a resistor on the serial port. Works, but you
> > get an IR transmit range measured in inches.
> >
> > - You connect the transmitter up to a wall tumour
> > style transformer and power the IR LED that way.
> >
> > Neither of the above is ideal. Then I ran across a
> > design that uses a high capacity capacitor as a
> > battery. The serial port is always trickle charging
> > the capacitor, and the IR LED gets its power off the
> > capacitor. As long as you don't go for high duty
> > cycles the IR LED should have a range in tens of feet.
> >
> > So, long range, and just one (serial) cable from PC to
> > IR box. Only downside is one pain in the butt part to
> > source (plus the previously noted smaller problem of
> > looking for a really nice looking way to package the
> > final result).
> >
> >   
> So, why not use a battery?


.... or an array of smaller capacitors in parallel, until you find the
right size.  This way you can test the design out and tweak it before
committing to an expensive part.  It's also the kind of thing you can do
right now.  

Batteries would definitely be simpler, though I understand not wanting
to keep replacing them.

-kms

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