Changing LCD display refresh rate

[cc1984]

Why not just add a condition that only updates the LCD if the ADC value changes by a certain amount from the last reading. That would reduce the updates and also make it less resposive to small changes in voltage.

[rsocor01]

Well, this is just an idea. Take 10 readings, then obtain the average, and display it in the LCD. Something like this,

MAIN:

FOR I = 0 TO 9
  ....Take ADC reading READING[I] 
NEXT I

'Next obtain the average
AVERAGE = (READING[0] + READING[1] + ......) / 10

LCDOUT $FE, 1, DEC AVERAGE

GOTO MAIN

Robert

[pxidr84]

How do that?

Here is a sample of my loop :

lp:

ADCON0.1=%1
WHILE ADCON0.1=%1:WEND

' Store ADC results
isense.HIGHBYTE=ADRESH
isense.LOWBYTE=ADRESL

' Security fault verifications
IF isense**40000>imax THEN flt=1

' LCD
idisp=isense**40000
lcdout $fe,$c0,$1,$20,"1 ISENS: ",DEC idisp DIG 2,DEC idisp DIG 1,".",DEC idisp DIG 0,"A"


goto lp

[Acetronics2]

lp:

ADCON0.1=%1 
WHILE ADCON0.1=%1:WEND

' Store ADC results 
isense.HIGHBYTE=ADRESH 
isense.LOWBYTE=ADRESL

' Security fault verifications
IF isense**40000>imax THEN flt=1

I = I+1    ; insert @top " I var Byte " 
IF I = 1 THEN  ; also can use IF I // 200 = 1 ... and adjust "200" to the desired rate

' LCD
idisp=isense**40000
lcdout $fe,$c0,$1,$20,"1 ISENS: ",DEC idisp DIG 2,DEC idisp DIG 1,".",DEC idisp DIG 0,"A"

ENDIF


goto lp

[rsocor01]

How do that?

Something like this,

lp:

AVERAGE = 0
FOR I = 0 TO 9
  ADCON0.1=%1 
   WHILE ADCON0.1=%1:WEND

   ' Store ADC results 
   isense.HIGHBYTE=ADRESH 
   isense.LOWBYTE=ADRESL
   
   AVERAGE = AVERAGE + isense
NEXT I

AVERAGE = AVERAGE / 10
ISENSE = AVERAGE

' Security fault verifications
IF isense**40000>imax THEN flt=1

' LCD
idisp=isense**40000
lcdout $fe,$c0,$1,$20,"1 ISENS: ",DEC idisp DIG 2,DEC idisp DIG 1,".",DEC idisp DIG 0,"A"


goto lp

[Charles Linquis]

A slightly different method:

Updating LCDs is really time consuming, from a PIC viewpoint. I find that a .25(once every 4 seconds) update rate is about right for most people, especially if it a two-line display.

The code below lets your code run at full speed and updates the LCD once every 4 seconds. Of course the rate can be changed to suit the user. It uses an ASM interrupt for low overhead.
Of course, you could read the timer directly, but I find that I always need interrupts anyway.

      DEFINE OSC 4 

     MasterClock VAR WORD BANKA SYSTEM
;----------------Timer Setup-----------------------------------  
    T0CON = 000010 ; /1:8   prescaler, tmr0 ON
;
;-------------------------------------------------------------     
   
INCLUDE "DT_INTS-18.bas"    '
;---------------------------------------------------------------
asm
    INT_LIST  macro     
        INT_Handler    TMR0_INT,  MainTimer, ASM, yes
       endm
    INT_CREATE              
endasm
''----------------- Initialization Done! -----------------------------
    Goto OverInt 
;----------------------- Timer INt ------------------------------------    
ASM
MainTimer
        movlw   0xCF         ;  100 mSec @ 4MHz
        movwf   TMR0H
        movlw   0x2C
        movwf   TMR0L
       
        btfsc   MasterClock + 1,7     ; Don't let MasterClock roll over
        bra     DontCount
        infsnz  MasterClock
        incf    MasterClock + 1          
        
      
DontCount        
      
      bcf     INTCON,2
    INT_ENABLE TMR0_INT
    INT_RETURN
ENDASM
;---------------------------------------------------------------------
OverInt:

   INTCON.7 = 1  ; Main Ints
   INTCON.6 = 1  ; Peripheral ints

    MasterClock = 0
@ bcf INTCON,2
@ INT_ENABLE TMR0_INT
TopOfLoop:
    If MasterClock >= 20 then     ; 20 X .1 sec = 2 seconds
       MasterClock = 0
         
         ; Do LCD routines here
    endif
    
        ; Your main program here
        
        goto TopOfLoop

[pxidr84]

There is no @ int_return at the end?
I already use a timer1 DT interrupt, this one will not affect my program?

[pxidr84]

Note : I use a 40MHz xtal, and my LCD desired refresh rate is about 0.5s.

[Charles Linquis]

The ISR is not written in PBP. It is in assembly. The only INT_RETURN you need is at the end of the interrupt service routine - just before the ENDASM.

For 40Mhz -
Lines you need to change

DEFINE OSC 40
T0CON = %10000011 ; Turn timer on, divide by 16 prescaler

movlw 0x0B ; 100 mSec @ 40MHz
movwf TMR0H
movlw 0xDC
movwf TMR0L


If MasterClock >= 5 then ; 5 X .1 sec = .5 seconds


And no, it will not affect anything else you have running.