Problems with a LCD (LPT)

Razzia · Post by **Razzia** » February 28th, 2007, 12:18 am

Hi

Im having some problems with my first LCD I hope you can help.

My LCD is a Winstar WH2004A-TMC-JS (4x20 blue/white). I wired it up using this guide: Image..

The company where I purchased the parts sent a wrong potmeter/potentiometer (is it called that in english?) Its the 10K they forgot and sent another one instead. Until I get the correct one from them, I have used a 50K.

When I plug it into the computer the backlight lights up. (can be turned off when turning on the 50K potmeter). I cannot get any text on the LCD. I have installed the Port95nt driver, LCD Smartie (5.3.2 final) + some other software that I want to use later on using plugins for Smartie.

In Smartie config I have the following: HD44780 -> Port 378, Driver boot delay: 1, Timing multiplier 4.

In the BIOS I have the following options: I have marked my choices with [x]

Parallel Port Address:
Disabled
378/IRQ7 [x]
278/IRQ5
3BC/IRQ7

Parallel Port Mode:
SPP
EPP [x]
ECP
ECP + EPP.

When I reboot my computer the LCD flickers a little and I can see the squares light up for a second.

I have triple checked my wiring and it looks perfect. Is the problem the wrong potentiometer or have I screwed up somewhere?

Best Regards
Rasmus Lauritsen

Edit: If someone wants to look at the data sheet for the LCD its here

Post by **limbo** » February 28th, 2007, 9:00 pm

use diagrams here to confirm your wirings
http://lcdsmartie.sourceforge.net/circuits.htm

You need to change that pot!

Razzia · Post by **Razzia** » March 1st, 2007, 12:50 am

My wirings are almost like theese
Instead of 10K pot I have a 47K and instead of 100 I have 10K. Between the 100 and pin16 I have 82 ohm resistor. That is what the guide I followed said.

Post by **limbo** » March 1st, 2007, 9:19 pm

The pot is the contrast controller, which means that even when you have no data (received from program) you must see two black lines (steady) and using the potentiometer you should be able to change the contrast.

I doubt you screwed something

. You just have to change this potentiometer.

Razzia · Post by **Razzia** » March 1st, 2007, 11:06 pm

I've have changed the pot and now my wiring looks like this. The LCD displays something from LCDSmartie but theres a lot of "noise" and the text is flickering.. Whats wrong this time ?

Edit:
The LCD should display this but it looks like this. (Sorry about the quality of the picture, but I was too lazy to find my digicam, so I used the phone.

Post by **limbo** » March 2nd, 2007, 7:04 pm

Seems that you have corrupted data...

The driver is correcty selected (you getting some output).

Sorry for been obstinate but please:

Check for any short circuit on your PCB.

Check the wiring once again.

Post by **mattcro** » March 2nd, 2007, 9:17 pm

How long is the cable between LCD and parallel port, and what sort of cable is it? There are a few posts about corrupted characters on LPT connected LCDs which may be due to the cable being too long or unshielded.

Does changing the timing multiplier (in Smartie driver config) have any effect?

Razzia · Post by **Razzia** » March 3rd, 2007, 2:47 am

mattcro wrote:How long is the cable between LCD and parallel port, and what sort of cable is it? There are a few posts about corrupted characters on LPT connected LCDs which may be due to the cable being too long or unshielded.

Does changing the timing multiplier (in Smartie driver config) have any effect?

I'm using this cable. It's 2m. Changing the timing multiplier does not change anything.

Post by **caesar** » March 3rd, 2007, 9:46 am

I had corrupted data with a cable exactly like yours and it was just 1m long.

I solved the problem by taking a 40 wide cable, and routing between signal lines an extra ground line (gnd, E, gnd, RW, gnd, RS, gnd, D0, gnd, D1, gnd, D2, gnd... you get the picture).

Good luck!

Fast351 · Post by **Fast351** » March 3rd, 2007, 2:00 pm

Remember with ground, you are returning the current going through the display, and all 8 data lines, and the strobe, and R/W pin. A single wire probably won't do it.

To test if this is the source of your problems, run a test wire from the display ground to your PC ground and see if your problems go away. An alligator clip test lead usually works good for this....

-Mike

Razzia · Post by **Razzia** » March 4th, 2007, 2:05 am

I just tried that trick with a wire from pc ground to pin1 (gnd) and it didn't help. Then I tried changing the pcb where I have the potentiometers, because there might be a short. Now I am absolutely sure, that there ain't no short on the pcb and the d-sub plug.

Then I plugged it into the computer again, and this time there was 2 lines of white bars flashing in steady rhythm. I started LCD Smartie again and now there is nothing on the LCD.

I didn't quite understand what caesar's suggestion. Can someone explain it to me in a simple language? Perhaps some sort of drawing?

And to display my total lack of electronic knowledge... Is it possible to install a potentiometer backwards? My potentiometers has 3 legs and therefore it is possible to turn it 180 degrees on the pcb. I hope you understand what im trying to say. Can't explain it any better.

Post by **mattcro** » March 4th, 2007, 1:38 pm

If you can see anything at all on the display (even corrupted characters or blocks), your potentiometers are probably OK. It's possible to install them backwards, but in your circuit the only effect is that you have to rotate them in the opposite direction to increase brightness or contrast.

Long cables (like 2 metres) can cause corruption problems. Something to try first is make up a short cable (like 30-50cm) to test. If the LCD works fine like this (leave it running for a while), you can try Caesar's suggestion.

What Caesar is suggesting is use a cable with more conductors, using the extra conductors as shielding to reduce interference and data corruption. This is how (good quality) printer cables are wired internally, and why there are 8 pins on the D socket that connect to ground - 1 for each data line. In your circuit diagram, these are the thick grey wires.

So you need a similar ribbon cable the the one you have already, but with 30 or so wires. Connect the 1st wire to LCD pin 1 as per diagram, then the 2nd wire to ground at both ends, 3rd wire to LCD pin 2, 4th wire to ground... and so on for LCD pins 3 to 14. You don't need the extra ground wires for the backlight connections (pins 15/16).

Developers: Just a thought... Has anyone measured the signal timing from the parallel port when Smartie is driving it? I wonder if the timing is unnecessarily fast (ie very short enable pulses etc) which causes problems for longer cables or weaker port output drivers. Is this timing handled in Smartie or the I/O driver?

Razzia · Post by **Razzia** » March 20th, 2007, 1:49 pm

Now I have changed the cable to another one, approx 50cm. I have used every second wire as ground and I tried shielding the cable with some aluminum foil.

That didn't work! I still have some corrupted characters and the display flickers a bit in both backlight and in the characters.

Is the display broken or have I screwed something up again?