Hello forum,

I've got a DEM16216 16x2 LCD module (http://www.cypax.com/pdf/DEM16216SYH-LY.pdf) and I got it up and running and I can write characters to it.

The problem is about the contrast - I think.

The LCD contrast input V0 is connected through a 330R to the wiper of a 10k pot. The V0 is bypassed with 100nF and the supply is bypassed with 10µF close to the module. The contrast is adjusted to max readability.

The problem is after the LCD has been initialized, it sometimes, not everytime it is powered, but sometimes (approx. half the times) writes my characters in the display, and then everything disappears from the display after a few seconds.

The other half of the times, the characters don't disappear.

This is what happens when the display fails:

1. Power is applied.
2. LCD is initialized and characters is written to it.
3. LCD displays the characters, but the characters are a bit dim.
4. 2 seconds later, the characters disappears.


This is what happens when the display is working:

1. Power is applied.
2. LCD is initialized and characters is written to it.
3. LCD displays the characters, but the characters are a bit dim.
4. 2 seconds later, the characters become clear, the dimming disappears and the characters stay on the display.

I have made a video where I connect and disconnect the power (5V) so you can see what happens. At first, the display is working, and the characters are displayed. Then I disconnect the power and reconnect it, and the display fails. Then I disconnect the power again and reconnect it, and the display fails again. Third time power is applied, the display works and shows the characters, but still with dim characters in the first 2 seconds (this is not normal LCD behavior as far as I know).

Link to video (2.5MB): http://www.futterama.dk/diverse/lcd.wmv
Faster download here: http://www.snapdrive.net/files/318051/Forums/lcd.wmv

Any ideas?

Regards,
Futterama

Attached Images

	lcd_setup.jpg (341.4 KB, 34 views)
	lcd_disp.jpg (320.7 KB, 23 views)

 

Update: As for now, it is working. I turned up the contrast and it seems like it's stable now. The only thing I did was leaving the LCD on for an hour or so and turning up the contrast after that.

Do a LCD display need "breaking in"?

 

Hey, Futterama,

Please remove the cap between pin3 and pin1. this behavior will go OFF. The voltage is charging the cap and after charging fully the pot value set by you is valid. After that the display is coming.
Also, the backlit appears too bright and it likely to interfere with the contrast optically. Try adding another 5 to 10 ohms in series with pin15 (LED+). It will reduce the brightness and the backlit life will increase.

__________________
Regards,
Sarma.

 

sir futterama:

what MCU did u use for the LCD? i have a problem making it work with a zilog MCU, i can't make it display characters.. all i have been able to achieve is the LCD displaying black matrices.. an experienced member at i didn't initialize it correctly..

 

I'm using a PIC18F2550. Any PIC will do. I'm using the CCS C-compiler. If you are using C, I can post my initialization code so you can get a few hints.

Are you using the exact same LCD module (DEM16216)?

 

The backlight supply voltage is 5V and the current is 90mA - the datasheet says 5.0V and 97mA, so I think its ok.

 

I was not taking of the absolute value.

The brightness as the photo showed was rather high. Nothing happens so immediately.

You can better operate the LED current at around 60mA to prolong the life of the display- I felt. In your case is around 90% of the rated current.

__________________
Regards,
Sarma.

 

I have another problem now. I left the project sitting there for a few days. Then I turned on the 5V power, and the display came on fine. After a few seconds, the whole display turns into garbage. The second row comes first, the garbage appears from left to right and covers the line. Then it comes from left to right on the first line. It covers the whole display in about 1 second. The connected MCU is doing nothing while this is going on.

Anyone knows what happens?

Edit: Actually, the MCU seems to be the problem. If I disconnect the power from the MCU in the middle of the garbage coming on, it stops.