SED1335 320x240 graphic LCD

[Demon]

Hi,

I thought I'd share the code I've come up with. As far as I know only Compsys has code for this controller, and it is for a smaller size. Since the setting parameters may not be obvious for some (like me, took me forever to figure this out):

(...figures, the source came out all misaligned in the text file...)

Robert

[Demon]

This is the code and circuitry to control the contrast and backlight via the PIC:

CLEAR
ADCON1 = 7

ASM
@ DEVICE PIC16F877, HS_OSC, WDT_OFF, PWRT_ON, BOD_ON, LVP_OFF, CPD_OFF,
WRT_OFF, DEBUG_OFF, PROTECT_OFF
ENDASM

DEFINE OSC 20

varContrast VAR BYTE
varBacklight VAR BYTE

varContrast = 100
HPWM 1,varContrast,32767

varBacklight = 200
HPWM 2,varBacklight,32767

' Here I have logic to scan 4 input buttons to increase/decrease varBacklight
' and varContast, then I reissue HPWM commands using new values.

END


Robert

[mister_e]

For the contrast line, you don't need any driver between your PIC and the LCD, a simple resistor in serie will do the job.... let's say in a range of 500 ohms - 2K.

[Demon]

Salut Steve! Donne-moi de tes nouvelles de ton voyage.

How will you adjust the contrast using just a resistor?

I wanted it so that both the contrast and backlight could be adjusted from 4 UP/DOWN buttons. Using transistors and HPWM was the cheapest way I could come up with. I now have a range of 256 steps for both controls.

Robert

[mister_e]

It will work the same way for contrast. You must keep your transistor for the backlight. For contrast, use HPWM and a in-serie resistor from your PIC to your LCD VO line. If this input don't need negative voltage, i have to work AS IS. Maybe you'll need to revert the values (0-255 to 255-0) but that's not a big deal.

[Demon]

I used a 25K pot at first to get the contrast working:

- Vss at one end with 0V.
- Vout at the other end with -30V (built-in negative voltage).
- V0 at the wiper.

For a good contrast, the V0 wiper varied from -20V to -24V, with -22V for a good setting.

Robert