PID-filter routine (2nd try).

[HankMcSpank]

Cool Henrik, I think I may have a use for this

Ok, this is a whole new area to me, here's what I think I've grasped wrt how this works ....

You have a desired value (setpoint), you take an incoming ADC reading & subtract it from your desired value....the PID sub routine then gets called & it returns a value of pid_out ?

Am I right so far?!!

Ok, what to do with pid_out?

For my intended use, I want to control a 256 step digital SPI pot (which alters the magnitude of an analog signal - an AGC in essence)...I have a 'desired value' ADC sample (a simple 8 bit ADC sample of the wiper from a std analogue pot ittingt between VCC & Gnd) that I want the signal to 'hit', but obviously the digital pot needs to either increment or decrement towards getting the signal to meet the desired value - I'm wondering how I translate the "Direction = pid_Out.15" to be increment/decrementof thedigital pot ...or does it not matter - ie will the value of pid_out just be a value that I can write direct to the digital pot?

What do I need to tweak with this bit...

Main_Loop:
    gosub adc
    pid_Error = Setpoint - ADValue      'Calculate the error
    Gosub PID                          'Result returned in pid_Drive
    Direction = pid_Out.15             'Set direction pin accordning to sign
    pid_Out = ABS pid_Out              'Convert from two's comp. to absolute
how to control the  digital pot here?!!!
    Pause 10                           'Wait....
    Goto Main_Loop                  '...and do it again.

I’m controlling my digital pot like thus…

write_VR1:    
    LOW CS    
    SSPBUF = VR1_Select   'put the command byte into SSPBUF
    gosub letclear
    SSPBUF = VR1_Position   'put the data byte into SSPBUF
    gosub letclear
    high CS
    RETURN
    
    letclear:  
    IF PIR1.3 = 0 Then letclear  ' wait for SPI interupt flag  
    PauseUs 10         ' 25uS fudge factor  
    PIR1.3 = 0        ' clear buffer full status
    Return

I’m figuring it’s just a case of something like GOSUB write_VR1 & then within there having the data byte be pid_out?

Hand holdng warmly accepted!