Changing LCD display refresh rate

[pxidr84]

Hi everyone,

In my program, the LCD commands are placed in a loop.

But the refresh rate of the LCD is too fast, so in certain conditions (when reading an unstable ADC value for example), the displayed numbers are changing very quickly, so it's unreadable.

So, it will be better if my LCD refresh displayed values every 200/500ms.

I don't want to use a delay/wait command in my loop.

Did the DEFINE LCD [...] commands can solve this problem?

Thanks a lot.

[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?