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

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