18/5/2000


Can of worms can of worms!
There is the simple way, then there is the correct way.
Just of interest the relevant specifications are:-

CISPIR 25 1995-11
ISO/TR 10605 1994(e)
Japanese blue book
ISO 11452 1995(e)
MIL STD 461D
ISO 7637 (Gives the impulse tests)
SAE J1112-13 1995
SAE J1113-42 1994

OK!
So for protection you can use a normal resistive divider and then pass this
into a ESD device like a California micro P002 etc.

Your main problems are susceptibility, we now are testing with values of up
to (Get this one people if you think your world is noisy! 200V/meter at
frequencies up to 0.5MHz and 40V/meter amplitude modulated by 80% up to
10MHz) Failure rates are dependant on the module requirements etc.

Dennis





> -----Original Message-----
> From: Gennette, Bruce [SMTP:bruce.gennette@TAFE.NSW.EDU.AU]
> Sent: Thursday, 18 May 2000 11:08
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [EE] Interfacing PIC to automotive electrics?
>
> 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.