David de Regt wrote: > The only problem I have with that is that it's still going > to have some ripple in it, even after being filtered. You need to stop waving your hands and provide some real specs. Zero noise on the analog ouptut signal is of course impossible. How much can you tolerate? What will this analog signal be used for inside the ECU? PWM lets you trade off resolution, bandwidth, and noise nicely. Without a real spec there is no way to know whether there is a workable tradeoff available via PWM. > so any ripple or anything like that > will cause some horrible fluctuations in the drivability of the car. *Any* ripple!!? Then forget about this project. Time to go home. Requirements like "zero noise", "exact" analog values and the like are silly and have no place in engineering. Good specification is the first part of any project. Problems posted here are often more due to vague specs than issues with PICs. > I'm also incredibly concerned about how I'm going to implement a pow() > function given the very limited PIC instruction set. I'm hoping not > have to do a table lookup, though that wouldn't be the worst case > scenario. I'd just need to eat 512 bytes of flash to do it... So? How big is the rest of your program? What exactly does it need to do? Unless you are contemplating something very complicated, I doubt you'll be anywhere close to filling up the 16K x 16 bit program space of a 18F2520, or the 16K x 24 bit program space of a 30F4012. (I mentioned the 30F4012 instead of the 30F3013 because you seem to care more about program space than 12 versus 10 bit A/Ds.) ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist