thanks for the suggestions so far,

the reason I want to do this is to

TOTALLY isolate the trailer from the tow-vehicle
as far as possible...

I want the tow vehicle to feel nothing, and only give
a ttl indication that a light is on...

thanks


----- Original Message -----
From: "Tony Nixon" <Tony.Nixon@ENG.MONASH.EDU.AU>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, March 05, 2001 4:24 PM
Subject: Re: [ot]: using a pic in an automotive application


> rad0 wrote:
> >
> > I remember seeing talk about people using a pic
> > on a 12v automobile system.
> >
> > What's the best way to isolate it from the high amp
> > perhaps spikey car system?
> >
> > The discussionwas lost from my archives, so what
> > did everyone agree upon for powering the pic.
> >
>
> There is a power supply circuit here. It is simple, but after years of
> use on 1000's of cars it appears to work ok. I doubt it would protect
> the PIC in a 'load dump' situation.
>
> http://www.picnpoke.com/projects/ignition.html
>
> Keep high power ground returns seperate from low power PIC circuits.
> I've had situations where a connection comes loose, and the ground tries
> to route itself through the PCB traces which tend to vaporise. The PIC
> still worked though.
>
> High power GND ____      _____ Low power ground
>                    \    /
>                     \  /
>                      \/
>                     ----
>                     ////
>
>
> > Is this totally out to lunch?  or could this reasonably be done?
>
> Only if you had a 'light' lunch ;-}
>
> > One, I want to totally isolate it from the auto-tow-vehicle as much
> > as possible.  And I'm not sure how to 'sense' when a particular
> > light is on.  I thought I could perhaps use a giant diode and some
> > sort of isolation to bring it down to ttl so I can connect it to my
> > pic.  Perhaps an optical isolator, is this practical?
>
> Perhaps a standard trailer plug and use the connections to drive opto
> isolators in the trailer circuit. I don't know if it is practical or
> possible to isolate the trailor earth from the vehicle earth.
>
> > Two, having a direct to battery buss and slamming lights on and off
> > of it might be a problem.  Is it?  Will this cause gross surges that
> > ought not to be done?  If so, how do you 'isolate' or buffer this?
>
> BD681 NPN transistors should be able to drive the 12V bulbs direct from
> a PIC pin (via base resistors). Bulbs are not highly inductive, so I
> doubt you will have any problems. Keep the circuit out of the heat
> though.
>
> --
> Best regards
>
> Tony
>
> mICro's
> http://www.picnpoke.com
> mailto:sales@picnpoke.com
>
> --
> http://www.piclist.com hint: The PICList is archived three different
> ways.  See http://www.piclist.com/#archives for details.
>
>

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.