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Can anyone confirm that this schematic is correct?



I've based it on the Eelco Schijf's schematic:



Can anyone tell me why pin 1 on the LCD is not connected directly to 5V..

Datasheet for the G121CB1P00C can be found here:
http://www.alldatasheet.co.kr/datasheet-pdf/pdf_kor/SII/G121CB1P00C.html

Thanks
sn1009

Reset is sometimes connected via that RC network to provide a proper reset during power cycling. When power is first applied to the circuit, the Capacitor holds the reset pin low until it charges. This ensures that all signals are sable when reset is disengaged.

As for whether it's right or not... I guess you'll have to try it and see. You'll soon find out if it works or not. But then look at my signature... and you'll see why I say this.

Personally, I would use a pot to adjust the contrast instead of your fixed resistors. I would also try the display with the INH pin held High, however I can't promise you that that won't cause damage... I just dont think it would... might show a brief flash of corrupted data on the LCD though.

Henri could give you a better answer to that....

_________________
Syridian,
http://syridian.com

I guess it looks mostly ok. The things I noticed are the resistors instead of potentiometer for the contrast adjustment and the connections to the INH signal. Why do have 3.3V at the input to the flip flop ? Also what are your plans with the flip flop ? I think I would just try feeding 5V to the INH input.

Thinking about it the INH input is a good idea but the problem here is that no lcd program to my knowledge supports this...

I can see that now.. But according to the datasheet I need to use the following power-up configuration:



The way I see it I can realize this by doing this:



And the delay for the INH pin during power up is set by a 80k resistor and 1uF capacitor..

But is it necessary with all these timing circuits.. I don't see it in all the other schematics found on this page..



Will do that.. The Vo is the contrast adjustment pin right?
In the datasheet Vo is described as adjustment terminal for liquid crystal driving voltage so I'm a bit confused..



The voltage has been changed to 5V. I've connected the flip flop in order to use a push button to control if the LCD is on or off..
I'm going to use diba's COM-port winamp control:
http://diba.hotbox.ru/comctrl/
..so by using the flip flop I am able to use the same push buttons for powering the LCD on and off as I am going to use for the winamp control..
And I think it looks better with a push button rather that a switch..

I am going to use the MAX749 to create the -24 volts.. I suppose that's ok.
The datasheet for the MAX749 can be found here:
http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1163

I think most lcd datasheets give similar power up sequence but people connecting lcds to LPT port probably just take the easy route and pretend never seeing that kind diagram

So do you think I should connect the LCD without all the timing circuits first and if that not succesfull I should add the timing circuits..

One thing that was bothering me the last time I tried to connect a LCD to the LPC port was the fact that I only got random characters on the LCD.. even after installing the port98nt.exe I never got the last LCD working with my motherboard because of that driver issue but now I've got a new PC and am ready to give it a try again..

If you want to make things right you should probably use the timing circuit. But I haven't yet bothered doing that with the displays I have used in LPT port. Also I have never used that display you have so...
It is always a risk not doing like the datasheet says but I haven't noticed that causing problems with the displays I have used. Also for most people building parallel lcds who might not exactly know why things are done like they are, adding and building additional circuitry could easily be a source of more trouble than what good it makes.

So I guess the final decision is yours to make.