Controlling LCD B/L

[solidus]

@ DEVICE pic16F876              ' System Device	
@ DEVICE pic16F876, WDT_ON      ' Watchdog Timer
@ DEVICE pic16F876, PWRT_ON     ' Power-On Timer
@ DEVICE pic16F876, BOD_ON      ' Brown-Out Detect
@ DEVICE pic16F876, LVP_OFF     ' Low-Voltage Programming
@ DEVICE pic16F876, CPD_OFF     ' Data Memory Code Protect
@ DEVICE pic16F876, PROTECT_OFF ' Program Code Protection
@ DEVICE pic16F876, XT_OSC
ADCON1=7
ON INTERRUPT GOTO KESME
INTCON = %11110000 ' Tmr0 aktif 
OPTION_REG = %01010101'Pull up dirençleri İPTAL- Bölme oranı 1/64.

Define LCD_DREG      PORTC ' LCD data portunu belirle 
Define LCD_DBIT      4 ' 4 bit'lik veri yolu 
Define LCD_RSREG     PORTC ' LCD register seçme portunu belirle 
Define LCD_RSBIT     2 ' LCD register seçme bitini belirle 
Define LCD_EREG      PORTC ' LCD enable portunu belirle 
Define LCD_EBIT      3 ' LCD enable bitini belirle 
Define LCD_LINES     2 ' LCD'deki satir sayisi
trisb=%11111111
TRISC=%11111101


LCDK VAR BYTE
Z VAR BYTE
Led_isik VAR BYTE
SAYAC VAR BYTE
LCD_Led VAR PORTC.1 
'tmr0=0 
Lcdk=0
BASLA:
PAUSE 300
LCDOUT $FE,$80,"HI!"
LCDOUT $FE,$C0,"LCD BACK LIGHT CONT."
LCDOUT $FE,$94,"B.0 & TMR0"

DISABLE 
KESME: 
if INTCON.1=1 then 
z=1 
Led_isik=0 
SAYAC=0  
Lcdk=0 
endif 
if z=1 then 
if Lcdk=0 then 
LCD_Led=1 
Lcdk=1 
endif 
SAYAC=SAYAC+1 
if SAYAC=62 then 
SAYAC=0 
Led_isik= Led_isik +1 
endif 
if Led_isik=8 then 
LCD_LED=0 
Led_isik=0 
SAYAC=0 
Z=0 
Lcdk=0 
endif 
endif
RESUME 
ENABLE
END

Hi I want to control LCD B/L with B.0 and Tmr0 interrupts. But still some problems. I can't find it. Pls Help me !!

[Charles Linquis]

The backlight of an LCD generally cannot be controlled through the digital interface.

You will need a FET (I use an FDC610) with the source connected to GND, the drain connected to the backlight (-) terminal, and the backlight (+) terminal connected to 5V. Your LCD may require a 5 ohm .5W resistor between the (+) terminal and 5V to limit the backlight current (check the datasheet).

Connect a 10K resistor between the FET gate and GND and also connect
the gate to a PIC output pin. Whenever you want to turn on the backlight, bring the output pin high.

[Melanie]

http://www.picbasic.co.uk/forum/showthread.php?t=794

[solidus]

Hi Melanie,
Do I have to use pwm for lcd lihgt ?

[Acetronics2]

Hi,

As I do not understand your comments and variables ( Turkish ??? )

One good question would be :

What do you want to do ???

- on/off control ??
- dimmer ??

Alain

[Melanie]

Well, you don't have to use PWM... but if you do, then you will have control over the Brightness and will be able to adjust for your own comfort level. If you have two PWM channels available, then you can do the same thing for your LCD's Contrast. Search the forum for Easy Contrast if you want to do that.

If you just want to turn your LCD's Backlight ON/OFF then any I/O Channel will do, but you must know how much current the Backlight will require... if it requires more than 25mA, then you need an external Driver of some sort.