Quote Originally Posted by mister_e View Post
How fast is enough? Do you detect some specific range/values, or just a threshold/single value?
Application is to detect a change in light intensity caused by an object passing in front of a confocally illuminated machine vision lens. It is battery powered so I want a low duty cycle illumination but fast enough to detect moving subjects.

What i'm thinking is a cycle that runs:

1) Light on
2) Pause enough for sampling cap to charge
3) Start AD conversion
4) Light off
5) Interrupt on conversion complete and compare new intensity to old - GOTO event handler if significant change
6) Pause and loop

What I want is a total loop time of <1msec or less. I can run a TAD of 2usec so it would only be 22usec for the conversion which to be honest is probably way fast enough. It just seems wasteful to do a 10bit conversion when I only want 4 bits of data !

Andrew