"Gennette, Bruce" wrote:
>
> Hi all,
>
> Probably been explained before, but how do I interface a 5V PIC to the
> signals coming from 12V car (and 24V truck) devices like temperature and oil
> pressure sensor/senders?
>
> I suspect that cars can use CMOS comparitors set against a trim pot (with
> zeners to divert any spikes), but how about truck (or boat) engines using
> 24V?
>
> Could I use voltage dividers to bring the signals down to the 0-5V range and
> directly connect to a PIC or TTL gates?
>
> For this first project I'm just looking at the alarm state ( !Ok ), but
> later I may want to log all parameters so that a progressive failure can be
> spotted (eg cooling water temp hotter each day indicates a growing blockage
> in the system or excessively worn pump).
>
> If there is an existing FAQ could someone point me to it please?
>
> Thanxs in advance,
> Bye.

There's an article about the network systems in cars in the current
issue of Circuit Cellar.. If you can't find it let me know I can look up
what the documents are you need. It basically tells you about the 2
major different kinds of car networks and what SAE manuals to get w/ all
the details.  I forget which issue (MAY perhaps april) but the cover is
mostly black :)

Let me know if you can't get ahold of it and I'll throw you some
pointers from the text..

                        Damon Hopkins