PID-filter routine (2nd try).

[HenrikOlsson]

Hi,
I'm sure you're correct that you don't need derivative. I'm surprised though that you get unpredictable results when you set it to zero, I'll have to look into that. What exactly is it doing?
Anyway setting it to 1 is pretty close to 0 (1/256 to be precise.) So it shouldn't have any effect on the actual control loop in your case.

The PID_Ki isn't the "reset time" (at least I don't think it's comparable to that), it's the integral gain. To get more integral action (steeper ramp) you increase the gain.

Here's how it works, basically:
Each time you GOSUB PID the integral term takes the error and adds it to an accumulator. It then increments a counter and compares the counter value to PID_Ti, if the counter value is less than PID_Ti it's done. If the counter is equal to PID_Ti it takes the (value in the accumulator) * (integral gain/256) / PID_Ti, it then adds the result to the output and resets the accumulator as to not overflow it. I think you can compare the PID_Ti value to what's sometimes called "reset time". (It does a couple of other things as well but lets not go into that right now).

As to a range of values for the integral gain..... all I can say really is that it's usually a lot less than the proportional gain, which in turn is usually a lot less than the derivative gain (which you don't use here).

Hope it helps.
/Henrik.