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CFAG12864I Contrast adjustments

tommy12345

New member
I have the graphic LCD CFAG12864Itit-n with a negative voltage generator. Does the display on/off instruction turn on and off the contrast also? I've adjusted a 10k pot to both ends and have not noticed any light. The lcd is generating negative voltage successfully.
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tommy12345

New member
I asked this question in the tech support forum but I think it is better placed here.

For the CFAG12864I series with an NT7108 controller, for the LCD to "come alive" does the controller need to receive the "display on" instruction?

I ask because I've applied power to the LCD. (5V pin2, -5V pin3, and ground pin 1 and 20.) ...Pin 18 (Vout = -5V) The data sheet says that the display on instruction turns on and off display data RAM pixels, But I should still see something even though the pixels are not on? Maybe I don't understand the difference between the back light and the contrast?
 

CF Support

Administrator
Are you supplying a current limited +5v to the backlight? If it's a negative display then it might be difficult to tell if anything is being displayed without the backlight powered.
 
For the CFAG12864I series with an NT7108 controller, for the LCD to "come alive" does the controller need to receive the "display on" instruction?
Yes.
But I should still see something even though the pixels are not on? Maybe I don't understand the difference between the back light and the contrast?
Have you written any data to the display? If not, there is nothing to see. Backlight is what makes pixels visible (for a negative display like the STI), and contrast is the ratio of brightness of an off-pixel vs. an on-pixel.

If you vary the voltage on Vo (pin 3), you should be able to make the entire screen go from dark to light. Putting -5V on pin 3 is probably not the right value; the spec sheet says -3.7V is typical for 25°C.

How is pin 19 connected?

You are not giving near enough info for anyone to diagnose your problem. Maybe you should attach your code file.
 
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tommy12345

New member
Pin 19 is connected to 5V through a 100OHM resistor. That might limit to much but I have not written any data to the display so I wasn't expecting to see any 'on pixels'. But when I range pin 3 from +5 to -5 the screen does not seem to go light and dark. The exact model I have is CFAG12864-ISTIT.

EDIT - thanks for your response btw.
 
You need to wire up a 10Kohm pot from +5V to -5V, with the wiper connected to pin 3, as shown in the data sheet. The range of Vo that changes the contrast of the display is relatively small, a few tenths of a volt + or - from the -3.7V given in the data sheet. Note that the Vo required depends on temperature.

Ah, I just noticed in your post in the other forum area, that you do have a pot connected. It occurs to me that maybe the LCD screen contrast will not react normally if the controller is held in reset. How do you have pin 17 wired?

I also think that expecting the display to "do something" without having control and data signals functioning is a waste of time.
 
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tommy12345

New member
Sorry for posting twice. :eek:

I think the 5V reference to my backlight could not source enough current. And for the lack of information, was because my question was more concerning the differences between contrast adjustment, and the backlight, and how that related to the "Display on" instruction, and less about help with my newb code :). I wanted to see the outline of dim little pixels before trying it out.

But I think I understand now, I will fix my backlight and see what happends. Thank you:eek:
 
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