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Help with understanding Vo and Vee requirements on CFAG19264D

oneten

New member
Hi Guys,

I have been working on a new project for a little while now and purchased a of CFAG19264D-TFH-VN, CFAG19264D-TMI-VN and Dev board CFA-10006.

This is the first time I have worked with Graphics LCD's and have produced from photoshop a whole library of characters and screens, which the dev board has been most helpful for.

I am now in the process of programming and testing the LCD in my prototype. I am using a Microchip PIC18F MCU and just have a question about the Vo and Vee pins on the LCD.
Character LCD's I have worked with in the past have not needed a Vee pin, but I see from the datasheet CFAG19264D LCD's have a crystal operating voltage above 8v.

I presume this has something to do with the need for a negative voltage pin (VDD - VEE (of -3v) would give a Vo around 8v) but dont really understand how this is best achieved.

In the past on LCD's that did not have a Vee pin I would just use a ~10k pot between Vdd and Vss to get Vo, but I am not sure what I should be doing with this LCD in relation to both the Vo and Vee pins?

I have a 5v feed into my Prototype PCB at the moment (which is stepping down from 12v) as I don't have a need for anything else to be above that at this stage, is there a way I can still drive the LCD or am I going to have to run a two-step regulator setup?

I also want to drive the Vo and backlight from PWM so they can both be adjust in software but again unsure of how Vee comes in to play here.

Sorry for the newb questions.

Cheers,
Hayden
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oneten

New member
Just came across this thread: https://forum.crystalfontz.com/show...ormation-needed-for-CFAG128128B&highlight=Vee

Makes more sense that the Vee pin is an output of the voltage generator for me to use on, say a 10k pot with my +5v Vdd and the wiper connected to Vo, this would give me my 8v crystal operating voltage.

I might be over thinking this but not sure if I could still use PWM off my MCU instead of a pot for a software adjustable solution rather than hardware, or if I should just redesign and go with a pot.

Any suggestions?
 

oneten

New member
Unless I did it with a transistor and just used the PWM output to pull the Vo line between Vdd and Vee....... Answering all my own questions :)

I also realized that you can adjust contrast Vo in software on the dev board with the standard basic scripts (although mine did not work for some reason), is this how its done there?
 

oneten

New member


:)

This is why I keep buying from CF instead of buying the cheap Chinese LCD's with useless datasheets.

So an opamp was used? Hmm...
I also noticed the SJ5 junction on my dev board is completely open circuit. Could this be why my Dev board contrast adjustment did not work when I first got it?
 

Attachments

CF Support

Administrator


:)

This is why I keep buying from CF instead of buying the cheap Chinese LCD's with useless datasheets.

So an opamp was used? Hmm...
I also noticed the SJ5 junction on my dev board is completely open circuit. Could this be why my Dev board contrast adjustment did not work when I first got it?
The jumper was unpopulated because the CFAG12864D series of LCD modules has an on-board potentiometer (VR, pictured here) which allows you to adjust the contrast on the module itself through a hole in the demonstration PCB. If you set this potentiometer to the middle of its range, you could then close SJ5 1-2 and then use the board (in theory) to adjust the contrast like you would expect.
 

oneten

New member
The jumper was unpopulated because the CFAG12864D series of LCD modules has an on-board potentiometer (VR, pictured here) which allows you to adjust the contrast on the module itself through a hole in the demonstration PCB. If you set this potentiometer to the middle of its range, you could then close SJ5 1-2 and then use the board (in theory) to adjust the contrast like you would expect.
So are you saying, in production I could leave both Vo and Vee disconnected and just use the onboard VR pot to adjust contrast?

Why is this not mentioned in the data sheet?

If so, thats kinda handy to know.
 

CF Support

Administrator
So are you saying, in production I could leave both Vo and Vee disconnected and just use the onboard VR pot to adjust contrast?

Why is this not mentioned in the data sheet?

If so, thats kinda handy to know.
That is what I'm saying.

I suppose it's not in the datasheet for reasons unknown. I'll forward this to our technical writer to see about getting that information into the datasheet.
 
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