Linear acceleration ramp

[Archangel]

I don't know if it will execute quickly enough but you could use a lookup table in a for next loop where the counter VAR is the lookup VAR.
example:
for i = 0 to 10
lookup i,[10,25,50, . . . . ] pulsevar
next i

[Charlie]

Although you said linear, I assume you really can live with a staircase.
If that's the case, and I understand the question correctly, then it's just simple math.

Your example: ramp from 10 (x) to 560 (y) in 42 seconds (n).
Suppose you want 1 step per second. In that case:
stepsize = (y-x)/n
output = x
FOR QQ = 1 to n
PAUSE 1000
output = x + stepsize
next QQ
Replace the pause with a 1 second interrupt if you need to do other things.
"output" feeds yout DAC

[pxidr84]

Although you said linear, I assume you really can live with a staircase.
If that's the case, and I understand the question correctly, then it's just simple math.

Your example: ramp from 10 (x) to 560 (y) in 42 seconds (n).
Suppose you want 1 step per second. In that case:
stepsize = (y-x)/n
output = x
FOR QQ = 1 to n
PAUSE 1000
output = x + stepsize
next QQ
Replace the pause with a 1 second interrupt if you need to do other things.
"output" feeds yout DAC

I will try that, thanks!

[SteveB]

On problem is the rounding error you will get with (y-x)/n

In your example: (560-10)/42 = 13.09524
But, PBP will only see 13. So, at the end of your routine, you will end up with 10 + (42*13) = 556

You will need to put in one line at after Next QQ:

Output = y

[SteveB]

Here is another alternative: Vary the period you increment your speed.
This examply uses PAUSE.

Incr_Time_ms = (1000 * Duration) / (End_Val - Start_Val)
Current_Val = Start_Val
Do Until Current_Val = End_Val
   PAUSE Incr_Time_ms 
   Current_Val = Current_Val + 1
Loop

What would be ideal is set up a timer and add a value so that it overflows after "Incr_Time_ms". You can then use interrupts, or just poll the flag bit. increment your "Current_Val", clear the flag bit, and then add the value to set up the overflow after "Incr_Time_ms". Wash-Rinse-Repeat until "Current_Val = End_Val"

[pxidr84]

Here is another alternative: Vary the period you increment your speed.
This examply uses PAUSE.

Incr_Time_ms = (1000 * Duration) / (End_Val - Start_Val)
Current_Val = Start_Val
Do Until Current_Val = End_Val
   PAUSE Incr_Time_ms 
   Current_Val = Current_Val + 1
Loop

What would be ideal is set up a timer and add a value so that it overflows after "Incr_Time_ms". You can then use interrupts, or just poll the flag bit. increment your "Current_Val", clear the flag bit, and then add the value to set up the overflow after "Incr_Time_ms". Wash-Rinse-Repeat until "Current_Val = End_Val"

Hi Steve,

I've used what you said, and I've also included a deceleration ramp:
(sorry for renaming the values, it's for a easier integration in my main program).

' PIC18F4431 initialization
DEFINE OSC 40      
DEFINE LCD_DREG PORTD
DEFINE LCD_EREG PORTB
DEFINE LCD_RSREG PORTB
DEFINE LCD_EBIT 6
DEFINE LCD_RSBIT 7


tacc var BYTE
tdec var BYTE
cacc var word
cdec var word  
ref var word
fmin var word
freq var WORD


tacc=1
tdec=10
fmin=10
ref=1200


PAUSE 4000
LCDOUT $fe,$1


cacc = (1000 * tacc) / (ref - fmin)
cdec = (1000 * tdec) / (ref - fmin)


lp:
   if freq<ref then PAUSE cacc
   if freq>ref then PAUSE cdec
   
   if freq<ref then freq = freq + 1
   if freq>ref then freq = freq - 1
   
   LCDOUT $fe,$2,DEC5 freq          
   if PORTC.0=%1 then ref=500
goto lp

It works quite good, but I cannot exeed 65 seconds (because 66*1000=66000, 16-bit integer is overflowed).
But, more importantly, I want to integrate the loop in a low priority DT interrupt. I really don't understand how you're using flags, etc. (I'm a beginner lol).

Thanks

[SteveB]

Here is a start (not tested!). But it should get you going in the right direction. I only included the acceleration stuff to keep the logic simpler.
You will need the include files (Get Darrel's from http://darreltaylor.com/DT_INTS-18/downloads.html), and make sure the file names match.

' PIC18F4431 initializationDEFINE OSC 40      
DEFINE LCD_DREG PORTD
DEFINE LCD_EREG PORTB
DEFINE LCD_RSREG PORTB
DEFINE LCD_EBIT 6
DEFINE LCD_RSBIT 7

tacc var BYTE
tdec var BYTE
cacc var word
cdec var word  
ref var word
fmin var word
freq var WORD

cacc_div VAR BYTE
cdec_div VAR BYTE

tacc=1
tdec=10
fmin=10
ref=1200

PAUSE 4000
LCDOUT $fe,$1

INCLUDE "DT_INTS-18.bas"
INCLUDE "ReEnterPBP-18.bas"
INCLUDE "TimerControl.pbp"  ; Timer Control Routines

ASM
INT_LIST  macro    ; IntSource,        Label,  Type, ResetFlag?
        INT_Handler   TMR1_INT,  _UpdateTickCount,   PBP,  yes
    endm
    INT_CREATE            ; Creates the interrupt processor
ENDASM

@   INT_ENABLE  TMR1_INT  ; Enable Timer 1 Interrupts  

GOSUB ResetTime           ' Reset Timer and mSec_Ticks = 0

IF tacc > 65 THEN
   cacc_div = 10
ELSE 
   cacc_div = 1     
ENDIF 

cacc = ((1000/cacc_div) * tacc) / (ref - fmin)
GOSUB StartTimer          ' Start Counting mSec_Ticks


Main:


     IF mSec_Ticks > (cacc * cacc_div) THEN
        IF freq < ref THEN freq = freq + 1
        mSec_Ticks = mSec_Ticks - (cacc * cacc_div)
        IF freq >= ref THEN
           GOSUB StopTimer
           GOSUB ResetTime
     ENDIF
     
   LCDOUT $fe,$2,DEC5 freq          
   IF PORTC.0=%1 THEN ref=500


GOTO Main

I may not be much use the next couple of days, but the building blocks are here (hopefully without too many errors/typos)

[Charlie]

Hi Steve,

It works quite good, but I cannot exeed 65 seconds (because 66*1000=66000, 16-bit integer is overflowed).
But, more importantly, I want to integrate the loop in a low priority DT interrupt. I really don't understand how you're using flags, etc. (I'm a beginner lol).

Thanks

Use a long for your variable - you'll have to work hard to overflow 32 bits.