LCD contrast negative voltage Supply Voltage(Logic)VCC-VSS--0.37.0VSupply Volta

I salvaged an Optrex DMF5001NY-LY-ATE-BBN 160x128 pixel graphic LCD. It uses T6963C so shouldnt be anything special about that.

Otherwise the schematic and display is clear to use but the LCD drive supply voltage is a big mystery. What should the voltage be? The display does not seem to have a built in charge pump.

In the datasheet it says that logic supply voltage should be -0,3V - 7V (VCC - VSS). This is clear. 5V from GND to VCC and it works.
But the LCD drive supply voltage is a mystery. It is stated as -0,3V - 30V (VCC - VEE). So if VCC is 5V, should VEE be 4,7V - 35V??? Or should it be negative -5,3V - -25V? This is the part I do not understand and would need help with.

Datasheet: [https://www.beyondinfinite.com/lcd/Library/Optrex/DMF-5001NY-LY-ATE-BBN.pdf

Thanks in advance!](https://www.beyondinfinite.com/lcd/Library/Optrex/DMF-5001NY-LY-ATE-BBN.pdf)

From your datasheet 4.2.Example of Power Supply
VCC = 5V
VEE = -20V
adjust the potentiometer for best contrast.
measure the actual voltage on the pot.
I suspect that it will be about halfway. i.e. -7.5V

Connect #3 (VCC) to 5V and #2 (VSS) to 0V
I suspect that pin #4 (VEE) on your module has generated a suitable -ve voltage.

Simple enough to try it.

David.

Thanks for the reply! I tried but get nothing on screen. Maybe pinout is wrong?

In u8glib the pinout for T6963 is: D0..D7, cs, a0, wr, rd, reset
On my screen I have: D0...D7, rd, wr, ce, c/d, halt, reset

Halt is not included in the library. I have connected it HIGH to enable clock. a0 and cs corresponds to ce and c/d. I have tried to connect both ce - cs and c/d - a0 and ce - a0 and c/d - cs but screen does not work.

I have left VEE disconnected, connected it to a pot (vee - vadj - vcc) and also connected it to GND and VCC. Nothing works.

LCD is blank wothout any life signs. When pot is connected, turning it does not make the screen go brighter or darker. It is just every time the same.

Any clues?

Connect #3 (VCC) to 5V and #2 (VSS) to 0V

Measure pin #4 (VEE) with a DMM.

What voltage do you see on the DMM ?

Connection as you said.

DMM black lead = VSS and red lead = VCC. Reading steady 4,92V

DMM black lead = VSS and red lead = VEE. Reading 4,32 V but starts to climb and stops at 4,7 V. Then it is wobbling between 4,6 and 4,7 V

DMM black lead = VSS and red lead = VEE. Reading 0,0 V

Well, it was not difficult to do. And you did not get a -ve voltage.

So it looks as if you will have to provide your own voltages.

Most 128x64 KS0108 / ST7920 / T6963C modules provide suitable voltages on the pcb. You just use a pot to adjust for contrast.

Many modern COG controllers generate all the voltages on the COG chip. And even allow you to select the appropriate values from on-chip ladder networks via software registers.
However T6963C is an elderly design.

David.

Thank you David for the help! Then I need to find a suitable charge pump for the screen.

Yes, you can make a charge pump and feed it through a few multipliers.
A handful of diodes and capacitors.

David.


Aliexpress item

Hooray it is giving life signs!!

I found in my drawers a step-up + charge pump circuit. It gives out +12v and -12V from 5-12V input. Now when I connect power, there is a line getting black for a small ammount of time.

Now just to get the code working!

Thanks for the help!

NusNus:
I found in my drawers a step-up + charge pump circuit. It gives out +12v and -12V from 5-12V input.

That will be a MAX232 or variant like the MAX233. RS232 interface. Certainly will do the job. :grinning:

The ICL7660 is the basic - original - charge pump IC but there are so many charge pump ICs nowadays (and possibly already included in the ATmega328 for its EEPROM) that it took me considerable time to jog my memory and find the name of the ICL7660. There are other derivatives on the Aliexpress item page I cited that operate at higher voltages FWIW.