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Topic: LCD is blank - No pixels (Read 610 times) previous topic - next topic

radioampdoc

Sep 14, 2016, 11:17 am Last Edit: Sep 14, 2016, 11:40 am by radioampdoc
Hi,

After searching the forum, I could not find a subject that included my problem.  I have had displays working with all kinds of Arduinos for the past 2 years.  Recently, I hauled out an uno and hooked up a new display to it.  It's the standard parallel interface I've used many times before.  After many checks of the wiring and changing out Arduinos and testing displays with other working projects,  I still get a blue, blank display.  I've tested all the voltages on the display.  Uploaded "Hello World" many times.  Nothing!
This is like I'm being punked.  Please look at the wiring in the picture and tell me what stupid mistake I'm making.  Sheesh this is embarrassing!

floresta

#1
Sep 14, 2016, 02:49 pm Last Edit: Sep 14, 2016, 02:52 pm by floresta
Start by checking the continuity of each of your wires.  

A photo with a little more illumination would help - things are a little murky on the far side of your UNO.  Also, some of the wires disappear off the top edge of the picture.

EDIT:  What happens when you disconnect all except pins 1, 2, 3, 15, and 16?  You should see the top row full of pixels and the second row blank.

Don




INTP

Have you played with the pot? Assuming that's what's wired up off screen.

floresta

Pin 3 appears to be connected to GND which should give ample contrast.

Don

INTP

Pin 3 appears to be connected to GND which should give ample contrast.

Don

I see an orange wire going off screen, no idea what you're referring to.

radioampdoc

#5
Sep 15, 2016, 06:18 am Last Edit: Sep 15, 2016, 06:26 am by radioampdoc Reason: Picture too big
I have tested all the wires and used different ones as well.  I get no pixels with data lines removed.  Remember, I tested the display with another circuit and it works perfectly.  VO has +2.8v currently.  I have tried adjusting the contrast bias with no result.  I also included a better picture of the wiring.  Sorry about that.

INTP

I highly doubt this has anything to do with it, but why are you running the backlight off the 3V3 instead of the 5V?
And how are you powering the Arduino (known, adequately powered USB port, or?)

radioampdoc

Using 3.3v for now just for testing.  However this is not relevant to my problem.

7v from power supply into Vin.  5v out from Arduino to display.  Power supply or usb; no difference in LCD.

david_prentice

Your JPEG shows the LCD pin#2 being supplied by 3.3V.   And VO pin#3 coming from the blue pot.

The LCD requires 5V on pin#2 and about 0.4V on pin#3.   As you vary the pot between 0V and 0.5V you will see some contrast.   If your pot has 2.8V on VO it will never show anything on the LCD.

An excellent clear photo.   An excellent strategy to use colour coded jumper wires to match your LCD pins.
Just supply pin#2 with 5V and adjust the pot to give about 0.4V.
It looks as if your Backlight Anode is connected to RESET and the Kathode to 5V.
So connect your backlight Anode to 5V too.   The Arduino 3.3V regulator is too wimpy.  The backlight Kathode to 0V.   

Incidentally,   life is much easier with an I2C backpack.   4 wires and you are done!

David.

radioampdoc

I Knew it was something really stupid...  Thank you very much David for pointing out the wrong VO bias!!  I never paid attention to the voltage on previous projects.  I always set it for comfortable viewing.
The wiring was correct all the time as I went over it 20+ times.
Thanks again!  You da man!!
Rudy

PS thanks to all of you who tried to help.

david_prentice

#10
Sep 15, 2016, 11:35 am Last Edit: Sep 15, 2016, 11:35 am by david_prentice
Your use of the international colour code for the jumper wiring is a very good idea (tm).

If it had been the normal lash-up with indistinct colours or wiring,   no one would notice it.  (or even bother)

David.

floresta

#11
Sep 15, 2016, 04:29 pm Last Edit: Sep 15, 2016, 04:36 pm by floresta
I see an orange wire going off screen, no idea what you're referring to.
On second thought neither do I!  I didn't spot the pot lurking in the upper left of the original photo either.

Don

INTP

#12
Sep 15, 2016, 04:52 pm Last Edit: Sep 15, 2016, 04:53 pm by INTP
Using 3.3v for now just for testing.  However this is not relevant to my problem.
Tricksy, I was wrong in a good way.

Thought your breadboard power rail was getting 5V and backlight only was getting 3V3

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