12F683 Maths and code genius reqd.

Dear Members

I have an 8mhz 12F683 monitoring a 2khz pwm signal. I am using pulsin to determine the high time and at 8mhz I get 5us resolution or 100 units over a 2khz 500us pulse. That's all fine.

I also have two rail to rail pots being monitored by 8 bits adc's and then multiplied to give 0-100 units resolution.
Again that's fine.

I am also using the pic HPWM to duplicate the incoming pwm data stream multiplying the incoming puslin data to provide the 8 bit hpwm data reqd. That's fine.

What I am doing is modifying the incomming pwm data using the two pots and then sending the modified pwm out of the hpwm.
The issue is my maths and logic seems horribly complicated.

Lets take a pwm signal with a high time of 51-90% I want to modify that with one of the pots called AssistPot so that

The first pot called AssistPot is only reqd to work on signals with a duty of 51-90%
1) When the pot is at 50% (in the middle) then it has no effect on the signal.
2) When it is 51-100% I want it to lengthen the pwm high time by 0-100% upto a maximum of 90% duty.
3) When it is 49-0% I want it to shorten the pwm high time by 0-100% down to a minimum of 51% duty.


The second pot called RegenPot does something similar but is reqd to only works on signals with a duty of 49-10%
1) When the pot is at 50% (in the middle) then it has no effect on the signal.
2) When it is 51-100% I want it to shorten the pwm high time by 0-100% down to a minimum of 10% duty.
3) When it is 49-0% I want it to lengthen the pwm high time by 0-100% upto to a maximum of 49% duty.

Now my code below works but feels clunky and I had to add a couple of checks to stop the maths going negative.
I think there must be a more elegant solution. The RegenPot maths seemed much harder.
I have it working using the code below and proteus simulates correctly. It also works with my hardware.
So I'm really looking for improvements, coding tricks or other brilliant insight :?

Code:

---

pulsin CmdPwrIn,1,CmdPwrHigh  'Measures length of Incoming CmdPwr 2khz Pwm Duty High pulse 
       
    If CmdPwrHigh > 50 then  'Assist Requested Duty > 50%
    PwrLevel = CmdPwrHigh - 50
    High Led    'Turn On Red Assist Led
    ADCIN 0,AssistPot          'Get AssistPot Setting
    AssistPot = (AssistPot * 100) / 255
    If AssistPot > 50 then
    AssistPot = AssistPot - 50
    Multiplier = 100 + ((AssistPot * 100) / (100 - AssistPot))
    PwrLevel = 50 + ((Pwrlevel * Multiplier)/100)       
    elseIf AssistPot < 50 then
    AssistPot = 50 - AssistPot
    Multiplier = 100 + ((AssistPot * 100) / (100 - AssistPot))
    PwrLevel = 50 + (PwrLevel-(((Pwrlevel * Multiplier)/100)-Pwrlevel))           
    elseif AssistPot = 50 then
    AssistPot = 0
    PwrLevel = CmdPwrHigh
    endif     
    endif
   
 
    If CmdPwrHigh < 50 then  'Regen Requested Duty < 50%
    PwrLevel = 50 - CmdPwrHigh
    low Led      'Turn On Green Regen Led
    ADCIN 1,RegenPot            'Get RegenPot Setting     
    RegenPot = (RegenPot * 100) / 255
    If RegenPot > 50 then
    RegenPot = RegenPot - 50
    Multiplier = 100 + ((RegenPot * 100) / (100 - RegenPot))
    General16 = ((Pwrlevel * Multiplier)/100)
    if General16 > 50 then General16 = 50 'Prevents Result Negative Overflow error
    PwrLevel = 50 - General16   
    elseIf RegenPot < 50 then
    RegenPot = 50 - RegenPot
    Multiplier = 100 + ((RegenPot * 100) / (100 - RegenPot))
    PwrLevel = 50 - (PwrLevel-(((Pwrlevel * Multiplier)/100)-PwrLevel))
    elseif RegenPot = 50 then
    RegenPot = 0
    PwrLevel = CmdPwrHigh
    endif   
    endif
   
    If CmdPwrHigh = 50 then
    TRISIO.4 = 1  'Turn Off Led 
    PwrLevel = 128 
    else 
    if Pwrlevel > 90 then PwrLevel = 90  'Prevent Assist request Error Duty > 90%
    if PwrLevel < 10 then PwrLevel = 10    'Prevent Regen request Error Duty < 10%       
    PwrLevel = (PwrLevel * 255) / 100    'Calculate HPWM Duty 8 bit data
    endif

---

Any Ideas?

I'm neither a math or a code genius and I'm most certainly missing something but how about this (compiles but not tested):

Code:

---

Temp VAR BYTE
AssistPot VAR BYTE
RegenPot VAR BYTE
CmdPwrHigh VAR BYTE
PwrLevel VAR BYTE

CmdPwrIn VAR GPIO.0

' 50 counts for 50% dutycyle @2kHz input and 8MHz oscillator
    PULSIN CmdPwrIn, 1, CmdPwrHigh             

' Read inputs (8bit mode!) and convert values to +/-40 in two's complement.
    ADCIN 0, Temp
    AssistPot = (Temp ** 20480) - 40
   
    ADCIN 1, Temp
    RegenPot = (Temp ** 20480) - 40

'-------------------------------------------------------------------------------
    IF CmdPwrHigh > 50 THEN                    ' Assist pot in play
        PwrLevel = CmdPwrHigh + AssistPot      ' No risk of overflowing a BYTE here
        If PwrLevel > 90 THEN PwrLevel = 90    ' But we need to clamp at 90% for top end...
        If PwrLevel < 51 THEN PwrLevel = 51    ' ...and at 51% for the bottom end.
    ENDIF
'-------------------------------------------------------------------------------
    If CmdPwrHigh < 50 THEN                    ' Regen pot in play
        PwrLevel = CmdPwrHigh - RegenPot
        If PwrLevel < 10 THEN PwrLevel = 10    ' Clamp at 10 for the low end
        IF PwrLevel.7 THEN PwrLevel = 10        ' Clamp at 10% if we went negative
        If PwrLevel > 49 THEN PwrLevel = 49    ' Clamp at 49% for the top end.
    ENDIF
'-------------------------------------------------------------------------------

---

/Henrik.

I'm afraid that does not work at all as expected.
Also the increase or decrease should be a percentage of the pot level.
Thanks for the idea though.

Opps sorry Henrik my simulation was not set up correctly your version does seem to be working and is half the size.

Still looking for any other ideas.

Thanks Peter

How can I simulate/enter this formula in a spreadsheet?
I want to experiment with the values for the the calculation.
The special 2's complement maths is making my head explode.
Thanks

ADCIN 1, Temp 'Temp = a number between 0-255
RegenPot = (Temp ** 20480) - 40

Hi,
Try something like:

Code:

---

=TRUNC((A4*20480/65536)-40)

---

Where A4 is the cell in which you put your TEMP value. Now, MS insists on changing the names of the functions depending on what language you're running but I think TRUNC is what you want, as long as you're running an English version of Excel - which I'm not.....here it's called AVKORTA....

This will give you a result of -39 when TEMP is 0 and 39 when TEMP is 255 and it truncates the result (instead of rounding it) just like it will when run on the PIC.

We could get it display as a real two's complement number but I'll have to dwell on that for a moment - if needed. In the meantime:
253 = -3
254 = -2
255 = -1
0 = 0
1 = 1
2 = 2
3 = 3

And so on.....

/Henrik.

How can i modify the formula to get +/- 20 or +/- 10

AssistPot = (AssistPot ** 20480) - 40
RegenPot = (RegenPot ** 20480) - 40

Hi,
+/- 20: Change 20480 to 10240 (1/2 of 20480) and subtract 20 instead of 40.
+/- 10: Change 20480 to 5120 (1/4 of 20480) and subtract 10 instead of 40.

Just think of the ** operator as multiplying by units of 1/65536.

/Henrik.