Troubleshooting an HD44780? 20x4 char LCD

Dwiel · 05-03-2004, 03:08 PM

Hello, I recently bought a charactor LCD and wired it up according to the ever so poular wiring diagram for parallel port with the 100k /10k pots. I turned everything on, adjusted the controls, and boom! I get the familiar 2 solid line default screen. Good start. I proceed to plug it into 2 different computers (XP/winamp/LCDdisplay and dos/MPXPlay) and try every bios setting for parallel ports, and even cut my 22ft parallel port cable down to 7ft.

Not once have I gotten anything but those two solid bars. Do you guys have any ideas on what I could try or what I could setup to test to see if the thing should be working, and what I need to do to get MPXPlay to use it? I also adjusted all of the settings in the .ini file to no avail.

I might try to get a couple bucks on ebay for it, and then buy a new one, but I am afraid that the same thing will happen the new one...

Any help on diagonising my problem would be appreciated!

Dwiel

BeamRider · 05-03-2004, 03:29 PM

Hi
I don't know your software but with my 20x4 I use jaLCDs.
Most LCD control software need a portdriver installed to work and frequently it has to be installed manually.
Look on the jaLCDs site and try with this software before buying another LCD

Dwiel · 05-03-2004, 05:02 PM

That LCD software is obviously for windows, but I only have Windows XP and DOS. I wanted DOS on my carputer for quick boot times, but should I install windows 98 JUST so I can try using software with it to test my LCD? I'll do that if that is the next logical step. I was just wondering if that program you refered me to handles XP... I did a quick look around that site and found that it is in anther language, so I couldn't really get much use other than the software itself.

Thanks for the quick response. I am gonna try the LCD with XP and then if that doesn't work, I'll go ahead and install 98 on my carputer.

Any other ideas?

Dwiel

Marsupial · 05-03-2004, 10:19 PM

I don't know any DOS applications for HD44780, but if you're to run it into XP, there is a need for a port extension
see
http://www.driverlinx.com/DownLoad/DlPortIO.htm
named port95nt.

If you haven't done that, you'll never get anything else then the test bars...

Dwiel · 05-03-2004, 10:41 PM

I have tried that before, and just to make sure, I just reinstalled it, and tried running jaLCDs. I am still only getting black bars.

I am installing 98 on my carputer as I type, and should be able to try that tommarow. My plan once I got 98 running was to first try winamp 2 + vis_LCDisp. I can also try jaLCDs.

What else can I do to get this thing working?

Thanks for the help thus far!

Dwiel

Dwiel · 05-09-2004, 08:45 PM

I can still not get my LCD out of the test pattern mode. :-( I installed Windows 98 on my target carputer, and have tried jaLCD, winamp plugin, etc. Does anyone have any more ideas?

Thanks!

Chairboy · 05-09-2004, 09:15 PM

I've made some hd44780 for microcontrollers, and I seem to remember putting a potentiometer on one line to play with the contrast. Your problem could be misadjusted contrast. Have you played with that pot once it's powered up?

Dwiel · 05-09-2004, 09:20 PM

what would need to change? I currently have tried with the contrast at full and at low. What would I be doing as I adjust the contrast? Just keep clicking the button to retry to connect/display I take it?

thx

Marsupial · 05-09-2004, 11:29 PM

what schematics have you used - seams its a circuit prob to me

check this one

also do continuity test on all connections and verify for shorts.

What have you done so far to test the circuit?

Dwiel · 05-10-2004, 08:58 PM

Thanks for the pic. I just checked the ciruit diagram I was using against your and they are the same. The one that I am using is at: http://www.myrolypoly.com/lcd_projec.../lcd-db25.gif:

I will go ahead and test for shorts, but I believe I have done this before. I think I will also test all of the connections going from the LCD to the male printer plug. I have tested from the end of the parallel port to the male end and from the wires comming from the LCD connecting to the parallel cable, but never the whole thing at once. Should be the same, but it can't hurt.

I was also going to test the parallel port out, but I didn't know what kind of software I could use this to test it with the voltmeter. Actually, now that I think of it, I can easily do this myself using the _outp() function in C++. I'll code up a quick test tonight and try to test it. The only computer I have Win 98 on is a bit flaky so I do not yet trust the parallel port.

I'll hopefully get back to you with what was causing the problems ;-)

Dwiel