Hi,
You need to sample your analog signal at precise intervals. Then, to find the rate of change, it's just a matter of comparing the last reading with the new one.

At what interval you sample depends on the expected rate of change of the signal. If it's temperature you should perhaps sample once every second, minute or even hour but if it's voltage perhaps once every mS or even faster - it all depends on the application.


/Henrik Olsson.