AVR-Chat

A couple questions: Are the resistors in the divider and the zener 
surface-mount devices or leaded devices? And what current is the vibration 
sensor capable of producing at 70 volts?

Chip components have a tendency to develop minute cracks when under a lot 
of vibration. I've had that happen before where the cracked part was 
easily seen but I had it happen recently where I couldn't tell which part 
was bad and just about went around the bend trying to find it. Leaded 
parts are less likely to crack under vibration.

Also, from my experience with zeners going bad, 90% of the time they 
become short-circuits when they go bad. If there's enough current behind 
the source to blow out the shorted zener, you're in trouble.

Other than those two areas, I'd say your idea itself would provide 
adequate protection.

Zack


On Mon, 17 Nov 2008, xolang1 wrote:

> Hi
>
> I have an ATmega128 utilizing the ADC to read voltage from a
> thin film vibration sensor that generates voltages from 0 - 70V.
>
> Im currently using a simple resitor voltage divider to scale down
> this 0-70V to 0-5V. To protect the ADC pin, i have a 5V Zener
> across the ADC input.
>
> Question: is this set-up sufficiently protected?
> any suggestions?
>
> Thanks in advance for the help.
>
> chris
>
>
>
>