PID Control HELP!!!

[cxiong]

Me again: Just try to make it clearer so you know my question

I try to work on the PID control subroutine by using the adc to control a pressure valve. My question is, when I have an output from the PID control equation, I want to (convert) or mask the output to a range 0-500 which is the # of steps for stepper motor control. For example, if my output from PID is

0 = 0 step (if output = 0, 0 step [Minimum] )
.
.
.
40 = 500 steps (if output = 40, then 500 steps [Max])

What is the subroutine to convert the PID output to step #?
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This message was ported from CCS's old forum
Original Post ID: 144516897

[Mark]

A const array lookup table would work nicely for this. Just create a rom array with your 41 values in it.

:=Me again: Just try to make it clearer so you know my question
:=
:=I try to work on the PID control subroutine by using the adc to control a pressure valve. My question is, when I have an output from the PID control equation, I want to (convert) or mask the output to a range 0-500 which is the # of steps for stepper motor control. For example, if my output from PID is
:=
:=0 = 0 step (if output = 0, 0 step [Minimum] )
:=.
:=.
:=.
:=40 = 500 steps (if output = 40, then 500 steps [Max])
:=
:=What is the subroutine to convert the PID output to step #?
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516901

[PCM programmer]

<font face="Courier New" size=-1>:=Me again: Just try to make it clearer so you know my question
:=
:=I try to work on the PID control subroutine by using the adc to control a pressure valve. My question is, when I have an output from the PID control equation, I want to (convert) or mask the output to a range 0-500 which is the # of steps for stepper motor control. For example, if my output from PID is
:=
:=0 = 0 step (if output = 0, 0 step [Minimum] )
:=.
:=40 = 500 steps (if output = 40, then 500 steps [Max])
:=
:=What is the subroutine to convert the PID output to step #?
-------------------------------------------------------------

So, your goal is convert an input range of 0-40 to a
output range of 0-500 ? That requires multiplication.

To find the multiplication factor, do: 500/40 = 12.5

So you need to multiply your input value by 12.5, to get
your output value. Here is one way to do it:

<PRE>
char input; // 8-bit input value of 0-40
int16 temp; // Temporary varible
int16 output; // 16-bit output value of 0-500
<BR>
temp = (int16)input; // Put input into a 16-bit variable
<BR>
output = temp * 12; // Multiply input value by 12
output += (temp >> 1); // Then add half the input value (.5)
</PRE></font>
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516902

[R.J.Hamlett]

:=<font face="Courier New" size=-1>:=Me again: Just try to make it clearer so you know my question
:=:=
:=:=I try to work on the PID control subroutine by using the adc to control a pressure valve. My question is, when I have an output from the PID control equation, I want to (convert) or mask the output to a range 0-500 which is the # of steps for stepper motor control. For example, if my output from PID is
:=:=
:=:=0 = 0 step (if output = 0, 0 step [Minimum] )
:=:=.
:=:=40 = 500 steps (if output = 40, then 500 steps [Max])
:=:=
:=:=What is the subroutine to convert the PID output to step #?
:=-------------------------------------------------------------
:=
:=So, your goal is convert an input range of 0-40 to a
:=output range of 0-500 ? That requires multiplication.
:=
:=To find the multiplication factor, do: 500/40 = 12.5
:=
:=So you need to multiply your input value by 12.5, to get
:=your output value. Here is one way to do it:
:=
:=<PRE>
:=char input; // 8-bit input value of 0-40
:=int16 temp; // Temporary varible
:=int16 output; // 16-bit output value of 0-500
:=<BR>
:=temp = (int16)input; // Put input into a 16-bit variable
:=<BR>
:=output = temp * 12; // Multiply input value by 12
:=output += (temp >> 1); // Then add half the input value (.5)
:=</PRE></font>

I think, he actually wants 40-500, which gives a multiplication of 11.5*, and adding 40. The same basic code will work, as:

char input; // 8-bit input value of 0-40
int16 temp; // Temporary varible
int16 output; // 16-bit output value of 0-500
output = 40; // put in the 40 offset
temp = (int16)input; // Put input into a 16-bit variable
output += temp * 11; // Multiply input value by 11
output += (temp >> 1); // Then add half the input value (.5)

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516913

[Sherpa Doug]

:=So, your goal is convert an input range of 0-40 to a
:=output range of 0-500 ? That requires multiplication.
:=
:=To find the multiplication factor, do: 500/40 = 12.5
:=
:=So you need to multiply your input value by 12.5, to get
:=your output value. Here is one way to do it:
:=
:=<PRE>
:=char input; // 8-bit input value of 0-40
:=int16 temp; // Temporary varible
:=int16 output; // 16-bit output value of 0-500
:=<BR>
:=temp = (int16)input; // Put input into a 16-bit variable
:=<BR>
:=output = temp * 12; // Multiply input value by 12
:=output += (temp >> 1); // Then add half the input value (.5)
:=</PRE></font>

For readabiltiy I would prefer to reduce 500/40 to 25/2.

output = (temp * 25) / 2 // Multiply input value by 25/2

I know my old ver 2.6x compiler would optimize this to a multiply by 25 and a shift. For anyone who has ever used Forth this should be obvious.

___________________________
This message was ported from CCS's old forum
Original Post ID: 144516917