Need help with understanding PID control

[Megahertz]

Thanks Henrik. I have got one more question for you, for now:

pid_Kp = $0700                     'Set Kp to 7.0
pid_Ki = $0080                     'Set Ki to 0.5
pid_Kd = $0225                     'Set Kd to 2.14

In your code above, you take $0225 to 2.14, $0080 to 0.5, how is that? I do not see calculations for converting numbers to decimal digits, as you are multiplying them as it is to the error variable. Please explain me how this is working and I will also be interested in knowing what is the maximum number I can assign to the gain this way, I will clamp it later as I intend to use pot for setting these. Cheers

[HenrikOlsson]

It's because the calculations are using the */ operator: 100 */ $0225 = 214
Since the gain variables (kp, ki, kd) are Words the max gain would obviosuly be $FFFF which is equal to an actual gain of ~255. Care needs to be taken not to overflow the output when large gains are used in system where the error cn be large.

/Henrik.

[Megahertz]

Thanks Henrik. So, is there any way I can tell what is the actual gain setting ( like 2.14 or 3.5 etc) before I multiply with 10 or 100. For example just by looking at lets say for example $0324?

I tried the following code, but my duty stays at 255 and is not coming down after overshoot.

'PROPORTIONAL VARIABLES
Error_P Var Word
Kp Var Word
'---------------------------
Kp=$0900

Main:
Gosub Get_Sensor_Value ' Get value from sensor

' ----- PROPORTIONAL CONTROL----------
Error_P=Set_Point-Sensor
Drive_p=(ABS Error_P) */ Kp
If Error_P.15 then Drive_P=-Drive_P

'--------------------------------------
Drive_T=Drive_T+Drive_P '(I used DriveT=Drive_T+... to keep some level of drive)
Duty=Drive_T
Gosub Duty_Mosfet
Pause 250
Goto Main

Duty_Mosfet:
If Duty>255 then Duty=255
If Duty.15=1 then Duty=0
HPWM 1,Duty,500
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