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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
:)
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
:)
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.
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
:)
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.
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
:)
DOH! sorry... always read the Datasheet first, always read the schematic correctly too (Vout) Tabarnak!
Where's the whip?
maybe another solution... maybe, if not, broke my legs... again :)
try it first. Place a 10K resistor between Vout and VO, on Vo place a 1K resistor in serie. Now send the other resistor end to 5 Volt. What happen with the contrast?
If i'm not dumb it should do something. If so, in serie with the other 1K resistor, place a diode in serie. Anode to PIC, cathode to resistor end. Is it working? I have some doubt on that so far... -voltage against 0V and 5 Volt+diode plah plah. I really need to return on a bench... feel rusty here!
$99 USD per LCD.
I can't afford to do magic shows with these suckers.
Robert
:)
anyway, forget me on the previous, it will work yeah but not on the range you said... your method is good, keep it.
Nice job you did! Any spare MAX232 output on your board?
I'm not using any MAX232...?
Why do you ask that?
Robert
:)
do a test... you'll see why sometime a spare MAX232 transmitter can be usefull. Place your voltmeter on a transmitter output.... set the transmitter input to GND, then to 5Volt. What do you get on your Voltmeter?
Sorry Steve, no time for a test, especially when I don't know what you want me to test. :) The few hours I have are spent trying to finish this never-ending project.
Robert
:)
SendData:
pinA0 = 0
pinData = varByte
pinWR = 0
@ nop ' <--- ADD
pinWR = 1
return
SendCommand:
pinA0 = 1
pinData = varCommand
pinWR = 0
@ nop ' <--- ADD
pinWR = 1
return
The [@ NOP] turns out to be very important for high-speed display, it corrects a timing issue. Without it, there is a sort of 'echo' on the LCD when you display characters extremely fast (my initial tests were keyboard-type speeds).
Robert
:)
Is it still the game project we already talked about about a year ago but just grow with the age :)
Yup, same project, but getting more complex as I learn more. Now I'm using a PIC 18F4550 at 48MHz with a high-speed USB link to a PC. I no longer process the game text on the PIC, the mcu is now used exclusively for I/O to and from the LCD and buttons, nothing more. VB6 will manage a database PC-side.
Robert
:)