View Full Version : spark fun huge lcd working great now but it makes no sense

01-04-2009, 04:16 AM
Hey guys I was going to just keep this one to myself but I just cant figure it out, I purchased spark funs huge LCD display a feww weeks and have been doing nothing but trying to get the darn thing to work , I even hooked up with a few others that were having the same trouble as me, Rayman and Ale tried to help by the way thank you very much guys! ...·The LCD would just would not work I am using Raymans drivers and test prop program now here is the funny thing
I have tested my wiring about 40-50 thousand times checked Rays code to the best of my abilties then every other day I would get Poed and throw it in my junk box well today pulled it out turned it on loaded Rays program and !!!!! it works just fine it displays Rays Hello there I am even able to write my own stuff Hello world and it works fine , I have done nothing differant and even trouble shot it with my scope and wrote down all the pin values it never worked So the big question is what is differant now that it works, well I put scope multi channel and logic analayzer on all pins D0-7 control wr,rd,ce,cd and they read the exact same as when the unit did not work, no cold solder joints, no shorted pins, same bread board same prop chip , same power supply I have double checked my notes so many times nothing has changed I find this troubling becuase it makes me wonder if my prop stick has some anomilty I am not aware of??? I have shut the display and prop·chp on and off all day and let it run for hour's it just keeps Working Fine!
I never did the whole prop test out pins as recommend in the class stuff becuase my other ones always worked fine , this propstick/usb took code let me set pins high and low and ran other programs with no problems but it had to be something, the other thing the other guys that could not get theres to work still do not work even though we verified pin for pin logic level.
Well anyway I would love to hear any thoughts or ideas I am thrilled it works but would love to know why id would not work for weeks ???
Also I am going to ask Rayman if I can re-print his code in the finished project section and post how to do a complete install of this LCD display to the Prop chip ·its· a very nice unit and is quite readable outside with no back light

Erik Friesen
01-04-2009, 04:26 AM
It could be for example, something like not having the 6x8-8x8 pin held low. Do you have resistors inline? How was the negative voltage converter controlled?

These controllers are kind of wierd. For example, it seems like a reset is not complete until the power is removed from the unit. I found that out in testing my program when some of the previous commands I had sent would remain in action through a reset the way I recall.

The first thing to check when running an LCD is that the contrast control is working properly.

01-04-2009, 05:08 AM
Erik the contrast always worked so did the back light I have a 10K pot between VDD and VEE the wiper is on Vo and that has worked since day one , the back light is just connected to 5 volts and ground and that has always worked, I have tied all the data lines high with 10K resistors and the control pins with 1K resistors, ground is clean and the reset is configured with a 10K resistor to +5 then one side to a 10u cap to ground and the res pin is in the middle of this config , that has always worked as well data sheet claims you need 6 clock cycles and I have that and a few more, I am at a total loss as to why this thing is working now
the only thing I can even remotely think of is my prop stick is being wierd but like I said it has now been working since 9:00 am this morning there is something on the data sheet about not letting Vdd be turned on before Vee or vice versus but its working and nothing has been changed since the first day I wired this up
I even double checked the actual LCD for good solder joints and re-touched a few it just would not work then today !!! Pooof its working I am one of those people that would like to know why before I commit this setup to a dedicated project I am building that will one day for no reason just stop working?

Erik Friesen
01-04-2009, 11:35 AM
Hmm. I am not using pull ups with my module.

Is the code you were working with previously identical to what works now?

If you are disposed to you could try my code just for kicks to see if that makes it go. You would have to change the display size in the constants and set the graphics size setup to reflect the same.

LCD's can be the most frustrating and the most rewarding it seems to me. It seems like you have talk to them just the way they want sometimes.

01-05-2009, 07:16 AM
Erik I would love to try your code, and yes I used the same code as before. do you have something knew or is it still the
T6963_demo program???? hey Erik is there some trick to using the search function here? I can not get it to do much of anyhting even when I know the name of a post?

Erik Friesen
01-05-2009, 09:42 AM
I have had problems using the search in the past too. Some people use the google search.parallax.forums or something like that.

I posted my code here and also in the object exchange.


Another forum member actually bought me a 240x128 to write code for. I think all you need to change is the constant specifying the pixel width and pixel height, and then in the graphics demo you will need to set the tile width and height in the constants(x_tiles & y_tiles) and in gr.setup you need to specify the tile width and height and center of screen.

to set the pins you set it in the code that calls start. It should reverse pins automatically. Loopset sets whether or not the screen updates from the buffer automatically or with a call to updatelcd.

PUB Start(WRpin,RDpin,CEpin,CDpin,RSTpin,DB0p,DB7p,loo pset)

I have tested this on my setup but could be there are a few changes needed to make it work properly on other screen sizes.