Looking for BIG capacitors.

[Colin McGregor]

--- Kareem Shehata <kareem-d+8TeBu5bOew5LPnMra/2Q at public.gmane.org> wrote:
> 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.  

Attempting to find capacitors anywhere close to 0.33 F
is an issue, It isn't like I could painlessly find say
two 0.16 F capacitors and run them in parallel :-( . 

Digi-Key looks like the route I will have to follow
:-( .

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

Exactly, avoid batteries if at all possible is my view
in all of this :-) .

> -kms
> 
> 

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