PID control loops - closed loop feedback

[Salik Syed]

yeah...i know i'm not gonna integrate twice...just once..(see code) but i was just wondering...
I've tweaked the code to include an integral term, now i'm wondering how to do the derivative...its hard because i'm trying to read ahead in the textbook...(we haven't learned derivitves yet!) ..... and then apply it to this....all the articles I find on PID are a bit too complex...
btw... we also did the whole tape interpolation thing for autonomous..we didn't use it because we didn't need the precision, we used a gyro to track heading, then tape for distance, we didn't have a legal gyro at times so i also implemented a timer that would measure time between the tape being seen and calculate dist to a much finer degree then 1/6 wheel circumfrence...alot like what u did...