If you use the power supply circuit shown on the page listed below make sure
the first 2 components can handle the FULL POWER demand of the rest of the
circuit.  For example, the protection diode and 22R resistor probably need
to be able to continuously pass 2 watts if your circuit draws 400mA @ 5V.  A
1N4004 diode can just take it, but you'll need 2 x 47R @ 1w resistors in
parallel to create a 2w 23R resistor.

Do some calculations, then give yourself a good safety margin in any power
supply design.  Personally I'd add an inductor ahead of the protection diode
in an automotiver environment to keep ALL electrical noise to a managable
level.

Bye.

> -----Original Message-----
> From: Tony Nixon [SMTP:Tony.Nixon@ENG.MONASH.EDU.AU]
> Sent: Friday, 5 November 1999 8:48
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: Car battery power help
>
> Mike M wrote:
> >
> > i need to connect a pic to my car, using the 12v car battery...umm i
> assume i can't just wire up the car battery to like a 7805 to control the
> voltage..or maybe im wrong...Suggestions?
> >
> > mikE
> >
> > Send someone a cool Dynamitemail flashcard greeting!! And get rewarded.
> > GO AHEAD! http://cards.dynamitemail.com/index.php3?rid=fc-41
>
> Check out http://www.picnpoke.com/projects/ignition.html
>
> 1000's of these have been working for years now, so I guess it works ok.
>
> --
> Best regards
>
> Tony
>
> http://www.picnpoke.com
> Email sales@picnpoke.com