How to test the LCD whether it works or not?

[smiles]

lcd dark squares

Could you tell me the way to test the LCD whether it works or not ?
I applied 5V to pin 2 and grounded pin 1, the first time I saw dark squares instantly on the screen but when I try again later, I see nothing on screen ??? Is it still work ?
Thanks !!!

 

[fala]

LCD question

The only way to test an LCD Alpha numerical/Dot matrix is to connect it to a microcontroller that has a test program running it. it should follow a very specific sequence of instructions before you can see anything useful in it called initialization.

 

[smiles]

LCD question

I program my Pic to display text on screen, but I don't sure about the code, so the code maybe also the reason for nothing on LCD, but first I have to sure the LCD work well ???

 

[melc]

Re: LCD question

Smiles,

All alphanumeric LCD's have a contrast pin (usually named VLC).
Applying the right supplying voltage to the module and a contrast potentiometer wiper to VLC (10K, the other pins either to +5V and ground or to +5V and -5V depends on LCD type), you'll see the graphic pattern (a dark rectangular symbol on the first line or half from the first line or on all lines, depends again by the LCD type) without any data connected to microcontroller. Turning the potmeter the pattern dissapear. That's the right voltage on VLC (pattern colour mustbe light gray)

 

[smiles]

Re: LCD question

Yeah ! I change value of varistor connected to contrast pin and at one position I see dark squares located in a right half of the screen, continue to change value, these dark squares disappear. Plug out and plug in the power again, I don't see these dark square again while rotating to change the value of varistor ???
So it still alive and my code is wrong :|

 

[fala]

LCD question

smiles, listen first what kind of LCD are we talking about alphanumeric or dot matrix. Alphanumeic LCDs are much easier and almost all of them are standard.
you have to check all lines connected properly, check it pin to pin with ohmmeter. after than you have to make sure that initialization process is exactly followed. if you have digital oscilloscope you even can check it that to be ultra sure.
Check each step of initialization, for example if you have alphanumerical make sure after each strobe LCD responds by pulling bit 7 low, if you send next command before previous command has been processed initialization will fail. Also make sure width of strobe and all signals are not shorter than minimum pulse width of that LCD.

 

[smiles]

LCD question

Thanks !!!
I follow HD44780 guidance for my 20x2 LCD but this LCD is of Epson manufactor, do you think they are the same, follow Hitachi and it still works with Epson ?
Can't find the datasheet from Epson

 

[FvM]

Re: LCD question

Hello,

alphanumeric displays could be expected to use a HD44780 alike interface, I never saw an exception. The differences are with graphic displays.

Regards,
Frank