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I have a 126x64 graphic LCD using HD61202/HD61203 controller chips. I have the datasheet for the LCD, and have wired it up to the parallel port using guides on the forums.

http://www.reloded.com/images/interface.gif

I followed the diagram below to wire my LCD up to the parallel port:

http://www.skippari.net/lcd/displaytech12864a.gif

Seeing as the model I have does not have a negative voltage generator on-board, I built one using the ICL7660S "Super Voltage Converter" chip:

http://www.reloded.com/images/negvolt.gif

I built the voltage inverter exactly as required based upon the above diagram, and feed the -5v to the VEE of the LCD. All other wiring on the LCD is correct (DB0-DB7, CS1, CS2, etc).

The only thing that I am unsure about is the LCD contrast wiring. Given that my LCD does not have a Vout (its not producing a negative voltage, it requires one), how should I wire up the contrast potentiometer? One leg should still go to Vdd I presume, and another to the contrast adjustment Vo, but I am unsure as to where the third leg should go? Maybe to Vdd? (Currently I have legs going to Vdd, Vee, and Vo, should it be Ground rather than Vee?)

I've tried 2 arrangments of the potentiometer, but neither one displays anything on the LCD. In fact, I have yet to get the LCD to even function at all. (Also, I cannot even tell which legs of the potentiometer are which, cant find any info on my particular model. Two of the legs are set back slightly from the third however? Would this generally make the third leg the output leg?

The +5v and Ground lines for the LCD are supplied via a modded 4-pin molex from my PC's PSU. Is there anything wrong in doing this?

Cable being used to attach to parallel port is 26-pin ribbon cable.


To me it seems that the contrasts should not really alter whether the LCD actually works or not, yet I have been unable to get it to do so. I've tried the KS0108 test program; clicking StartDriver, then Initialize LCD is fine (LCD doesnt actually do anything visibly though, should it?) but when I then click Test or Show BMP, the program hangs/crashes.

The only other thing that I can think is that the LCD itself is broken. When wiring it I had to take off the metal cover over the screen itself, and the screen did come off after this (the screen and rubber contact bits along the top and bottom) could this have damaged the screen in some way? I did put it back on carefully and reattached metal cover, and it should be lined up correctly with the contacts on the LCD's PCB.

I'm totally at a loss, other than the contrast not being wired correctly and causing the LCD not to be detected or function at all (shouldn't it display *something* just when it recieves power?) I cannot think what would be causing my problems.

Any ideas would be appreciated

[EDIT] The datasheet for the LCD says the Logic supply voltage (VDD) is Min 0v, Max 7v and the LC driver supply voltage (Vo) is Min 0v, max 24v

Should I be supplying more than 5v to the LCD?

you have 3 connections on the potentiometer , one connect to GND ( E as the schematic ) the other one ( A ) to your negative power suply you made .

the middle connexion (S) ( shoud be the mobile part of the pot' ) link the contrast . well , where is the contrast ? so if you can check , may be Vo and VEE are link together inside your lcdmodule . if not try to connect first on VEE . and after if nothing work yet try Vo . (i think is Vo )


on the pot the two leg right and left should be A and E the leg on the middle is S . if not check with multimeter ( ohms ) and look the Ohms value change between A and S when you move the pot , it should do the same thing between E and S. the value between A and E doesn't change at any time .

Do you have a link to the datasheet so I could have a look ?


The middle/output pin should be going to Vo. Other pins should go to GND and Vee or Vdd and Vee. I'd like to see the datasheet for this.


Probably yes.


Should be fine.


If the contrast voltage isn't set right you shouldn't see anything on the lcd. When the contrast voltage works you should be able to set the lcd to completely dark and light by turning the contrast potentiometer.


You're right, it shouldn't cause anything visible.


If the contrast voltage isn't correct it shouldn't show anything. I'd like to see the datasheet for the correct contrast voltage.

Here's the datasheet, having looked over it, I think my negative input voltage should actually be more like -19v rather than the -5v i was trying to use.

Will have to look over it when I get back off holiday

http://www.reloded.com/files/Densitron%20LM3328.pdf

Yes, these two pictures should show how to connect the voltages and what voltage is needed:


What this is saying is that at 25C the Vdd to Vo voltage should be 14.6V. As the Vdd is +5v you need at least -9.6v for the Vee. So maybe -12 would be good value for Vee but -10v should be enough.


From here you can see how to connect the contrast potentiometer (Vr) between the voltages and lcd pins.

Well, 12v worked just fine had to swap cs1 and cs2 (which surprised me) and am having some trouble getting things positioned correctly on the screen, but, it works!

well done !