128x64 graphic lcd

ertansuluagac · Joined: 13 Jul 2017 Posts: 135 Location: IZMIR

I am asking for a 128x64 graphic lcd. (model no. WG12864I)
- Do I have to use the vee pin? What does Vee pin do?
-If I have to use it, what is the reason?
-If I don't have to use it, what's the reason?

Finally, how is the connection? I saw in the datasheet that the potentiometer connected to the gnd end, to the VEE pin. Is it correct?

vee pin connection

http://embedded-lab.com/blog/lab-20-interfacing-a-ks0108-based-graphics-lcd-part-1/
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Es

Ttelmah · Joined: 11 Mar 2010 Posts: 19546

I think you are talking about Vo. This is the voltage that sets the
substrate level for the LCD, and effectively sets the display contrast.
You normally have to be able to adjust this over a particular range
to give the required display. Hence a pot between Vss and Vdd.

temtronic · Posted: Sat Apr 18, 2020 4:29 am

Curious was I, so....
I googled 'WG12864I' and downloaded a datasheet from Winstar. On page 11 they show a 10K to 20K pot connected to VDD, Vo and Vout. VDD is +5 power, Vo is the input to control contrast and Vout is the -ve voltage generated by the LCD.
While most 'text' LCD modules will work with the lower leg of the pot connected to gnd, this 'graphic' LCD module has it's own power supply for 'contrast'.
It might actually work if connected to gnd, but may be very 'sensitive' to get just the right level of contrast. Measure what voltage range is rewquired, and simply add fixed resistors to 'trim' the pot.
I'd connect as the datasheet says using a 1k or 20k '10 turn pot', not a 'volume control' style pot.

All LCD modules originally need a -Vee to 'light them up', then over decades manufacturers reengineered them to use the simpler,cheaper,easier single voltage power interface. This allowed them to sell millions and millions of them !

ertansuluagac · Joined: 13 Jul 2017 Posts: 135 Location: IZMIR

ok I know you said this for Vo. So you are talking for 3 legs of the lcd. I have a question, vee pin with 18th leg. That is, the negative voltage output leg. What is that ? and why it is used ? Or what is the purpose of use ?
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Es

Ttelmah · Joined: 11 Mar 2010 Posts: 19546

OK. This display is one that may still require a -ve voltage for Vo.
To simplify this the manufacturer has an option for a small -ve supply
generator built in to the unit.
Vee is this -ve voltage.
The pot feeding Vo potentially needs to run from Vee to Vdd.

However it then gets slightly more complex.... There are a
number of different versions of the display with different colour LCD's.
These are distinguished by a letter in the part number. After the part
number there are three letters xxx. The first is the type of backlight,
the second the type of actual LCD. Then a V or an N. Now the LCD type
and the last letter determine what voltage is actually on Vee, and whether
it is actually needed.
On ones without the -ve generator, the pot needs to run between Vss and
Vdd. On ones with the -ve generator the pot needs to run from Vee to Vdd.
So whether you need to use Vee, depends on the full part number of your
LCD. Now on some of the displays the data sheet shows pin 18 as NC
on others Vee is shown as present. If it is present, then it needs to be
used to feed the contrast pot.
If the part number of your display has a -V at the end it has the -ve
voltage generator and this needs to feed the bottom of the contrast pot.
If you don't know the full part number, you could check if there is a -ve
voltage on this pin, by applying power and testing with a meter. If it is it
needs to be used.
I pulled two data sheets for this part. The first has no mention of Vee
and has the pot running from Vss to Vdd. The second has Vee and the
pot running from Vee to Vdd.