Spehro Pefhany wrote:
>> I also didn't update cur_pwm correctly -- it 
>> seems the P+I+D value is supposed
>> to be added to the output control variable, not used as the control variable.
>> That makes sense, as it's based on the error 
>> (delta-V), not the absolute value.
> 
> No it doesn't make sense (unless you're trying to use the so-called 'velocity
> (PID) algorithm', which I don't suggest. If you add the error to the last
> control output, you'll always have integration, right?

Ah. OK. But what about this situation:

Target = 2V
Input = 2V
Error = 0
Current P = 123 (example)
P = (Kp * Error) = 0

So as soon as it hits the target, it's going to reduce the output to 0. In 
other words, it's always going to oscillate.

> Note that the control output goes DOWN as the PV goes UP.
> 
> y = P * (SP-PV) + K
> 
> Suggest you get this working first.

Will do.

> Why not just set MIN_PWM to 32 ?  The maximum should also be set so it allows
> you the measurement time you need.

Good point...
MAX_PWM is already set to allow about 700us measurement time (the 650us delay, 
plus 50us processing time). If I remember correctly, that is -- I've just done 
a reinstall on the PC (prompted by a hardware upgrade) and MPLAB isn't 
installed yet.

Thanks,
-- 
Phil.
piclist@philpem.me.uk
http://www.philpem.me.uk/
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