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Topic: 12864ZW with u8glib - no DI pin?! (Read 3660 times) previous topic - next topic

AxlRose94s

It doesn't work  :(
Quote
If I dont connect to GND the PSB pin, the display lights, but doesn't print the instruction of the Helloword code.

i noticed that the PSB pin has an output voltage! Now it explains because when I connect it to gnd Arduino turns off. it goes at short circuit!
WHY??  :smiley-sad-blue:

olikraus

PSB might have a pullup resistor.

Do the following: Apply
1 VSS 0V
2 VDD 5.0V 
Then measure the voltage between VSS and PSB. What is the voltage?
Then measure the voltage between VSS and Vout. Waht is the voltage?

Then do the following:
Connect
1 VSS 0V
2 VDD 5.0V 

Vout to the first pin of the variable potentiometer
V0 to the second pin of the var pot
VSS to the third pin of the var pot.

What do you see, when you turn the var pot from left to right?
Expected result: You should be able to turn on and off all the pixel. Is this possible?

Oliver

cider101

#17
Feb 02, 2014, 06:09 pm Last Edit: Feb 02, 2014, 08:37 pm by cider101 Reason: 1
i'v got the same problem here...can't get the qc12864b /st7920 to display anything in serial mode. As soon as I connect the PSB to ground, the backlight led goes of.

having the red probe on VSS, the black on PDB/Vout i get the following results:
VSS-PDB  = -5.1v
VSS-Vout = -4.5v

Did i understand the instrucutions in the previous post correct, that i have to desolder the pot on the back of the display module and replace it with a new one connected to Vo/Vout/Vss ?

Edit:
thats my setup:
/*
LCD       Arduino
4 - RS       10 (cs)
5 - R/W    9 (mosi)
6 - E       8 (clock)
17 - RST   7 (reset)
*/
U8GLIB_ST7920_128X64_1X st7920(8, 9, 10, 7);

Edit2:
backlight doesn't goes off, if i pull the PSB Pin down with a 10k resistor (which i obvously didn't use before).....did i eventaly fryed my display ?

olikraus

The PSB pin is a digital input of the controller. It should never have an effect on the backlight.

Assuming, that the person who designed the PCB was right, a desoldering does not make too much sense to me.

Also your setup looks correct.

Oliver

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