PID-filter routine (2nd try).

[HenrikOlsson]

Hi,
The very first thing to tend to, IMHO, is to make the update rate as stable as possible - it is very important for stability. If you haven't already seen it, here's a pretty good article on digital PID filter implementation. It's a good read even if you're not actually writing the PID filter code - just using it.

Keep at it and keep us posted!

[Ioannis]

I recall downloading that article, but did not read it. Will do.

My pre-PID implementation was based on a loose control loop like this one:

if out_value < (setpoint - 1) then
    pwm_signal=pwm_signal+1
endif

if out_value > (setpoint + 1) then
    pwm_signal=pwm_signal-1
endif

It is a very simple idea that gives also a hysteresis of +/-2 points. So if the out_value is within the "dead band" nothing happens.

The down side is that, depending on the overall loop it may take too long to reach the setpoint and also may do some oscillations also if there is delay getting the correct analog feedback.

My first impressions using the PID is that has the potential to be very fast and accurate, despite the fact I did not managed to make it work reliable yet.

Will come back after correcting the setup.

Ioannis