Filtering supply lines

[Oliver Scholz]

First of all, thanks to all of you for your helpful suggestions and
explanations!

I did some databook browsing, and I came across two chips that may
be particularly suited for our purposes:

LM2937 and LM2940 (National Semi)

These two are low drop linear voltage regulators with 0.5A and 1A current
respectively. Make sure you *dont* get the LM2940C (commercial) version,
because the other one is specifically for automotive purposes,
it is protected against load dump, positive and negative spikes, shorts,
thermal protected, 2 battery jumps, etc.

> could be the braklights drawing excess current from your system.
I dont think so. There are other devices that draw more current and dont
introduce spikes. I suspect the cruise shutoff solenoid makes a heavy
spike...

> >c) use of a shielded cable for the display (need to tear apart instrument
> panel again)
> 
> Most definately. Unshielded cable + any appreciable baud rate + 5' or
> greater run + car environment = noise on lines.
I will try that, it is a cheap fix anyway...

>  I think a good linear with adequate caps should work, especially if you are
> only needing 100ma. But I do not have a lot of experience in automotive
> applications.

I think so too. The CPU runs fine anyway, no crashes under any circumstances.
Ah well, I will try the shielded line and separate battery ideas...


Thanks again!

Best regards,

-Oliver