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Contrast on LCD -CFAG12864BTFHV

Sam

New member
The backlight for my LCD is working fine. However, I tried a series of programs found online to test the LCD, nothing owuld appear on the display. This leads me to believe the maybe its the contrast wiring thats the problem.

I do not have a potentiometer to set the contrast between Vdd, Vo and Vee. However, I have managed to place resistor accross these pins to make up the 10K ohms. and put pin3 to about 1.7V?

My pinout is like the following: Pin 1 --> 6.6K ohms --> Pin3 then Pin3--> 3.3k ohms -->Pin18.

Would this be adequate? If not, how can I avoid using the potentiometer and test that the LCD is wired properly with contrast before I start programming?

Does the difference between pin1 and pin8 have to be 10K? Because if I wire like this, Pin3 will be approx.-3V
Pin1 ---> 13.2Kohms--->Pin3 then Pin3--->3.3kohms--->Pin18

(sorry, I only have access to 5kohms and 3.3kohms for now,
I'll try to have Pin1-->8kohm-->Pin3 and Pin3-->2kohm--->Pin18 if you think this will do the trick)

How does the contrast change according to the voltage across these pins? If Vo is -5V, -3V, 0V, 2V will I see anything in the LCD? Would the screen appear darker even with no program?

Its my first time working with microcontrollers and LCDs so my programming isn't too great.
Since after programming the LCD it still appears blank, I need to figure out whether my wiring or programming is the problem.

Another question I have is what to do with pin14?

Thanks,
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... how can I avoid using the potentiometer and test that the LCD is wired properly with contrast before I start programming?
You can use the fixed resistors, but you will have a hard time getting the best contrast because the useful range of adjustment is only about a volt.
Does the difference between pin1 and pin18 have to be 10K?
No, the data sheet recommends 10K to 20K
How does the contrast change according to the voltage across these pins? If Vo is -5V, -3V, 0V, 2V will I see anything in the LCD? Would the screen appear darker even with no program?
The voltage where the screen starts to darken is about -2 volts (measured to ground). About -3 to -3.5 volts will give good contrast. More negative than -4 volts will make the screen entirely dark. Note that Vlcd is specified as "Vdd-Vo", so a Vlcd of 8 volts means 8 volts below Vdd, which gives -3 v.
Another question I have is what to do with pin14?
Pin 14, reset, is taken low for a few milliseconds, and then taken high, before you initialize the display. Reset stays high during normal operation. If it is kept low, the display will not function.
 
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