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OLED diplay misalignment with Beaglebone Black
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OLED diplay misalignment with Beaglebone Black

by a_power on Fri Apr 27, 2018 5:49 am

Dear all,
I have a Monochrome 1.3" 128x64 OLED display connected to a Beaglebone Black. I am working with the SPI bus and I am using the python examples furnished by Adafruit. It is working correctly with the shape.py example.
Now, I am trying to display on the full screen some "A" and then to switch to some "B" with a refresh rate of 1 s. In the picture "Good Screen view", you can see some "B" as I said.
However, from time to time, I see something strange in the display, such as a misalignment on the screen and I cannot understand what is going on (image "Bad Screen View").
I tried to take a look to the SPI signals, to the Reset and the DC signal on the oscilloscope and they seem to be good (even if it is not possible to trigger on an event giving a bad screen view)
Do you have any idea about what is happening?
Thanks a lot.
Attachments
Bad_screen.jpg
Bad screen view
Bad_screen.jpg (36.22 KiB) Viewed 261 times
Good_screen.jpg
Good Screen view
Good_screen.jpg (36.74 KiB) Viewed 261 times

a_power
 
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Re: OLED diplay misalignment with Beaglebone Black

by a_power on Fri Apr 27, 2018 6:07 am

Dear all,
one more screenshot that can be useful.
As you can see, at a certain point, the "A" character is missing the horizontal line, which seems to be below; from that point, something strange happens.
Thanks for your help.
Regards.
Attachments
Bad_screen_2.jpg
Bad_screen_2.jpg (46.99 KiB) Viewed 257 times

a_power
 
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Re: OLED diplay misalignment with Beaglebone Black

by drewfustini on Sun Apr 29, 2018 3:22 am

It would be good to determine if the behavior is that results of your particular OLED display or a bug in the Python library.

Are you able to try controlling the display from an Arduino to verify it works reliably with Arduino library?

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Re: OLED diplay misalignment with Beaglebone Black

by a_power on Wed May 02, 2018 3:41 am

Dear DrewFustini,
thanks for your answer. Actually, I have not an Arduino with me to test it.
I tried with two different OLED displays and two different Beaglebone Blacks, obtaining the same results..
Thanks for your help.

a_power
 
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Re: OLED diplay misalignment with Beaglebone Black

by drewfustini on Wed May 02, 2018 11:51 pm

What is the model number of the OLED?

If I have the same one, then I will try to reproduce the issue.

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Re: OLED diplay misalignment with Beaglebone Black

by a_power on Thu May 03, 2018 5:24 am

Dear DrewFustini,
thanks again for your reply. It looks like it is a problem of my hardware.
I have 10 ohm connected in series on the SPI Data and Clock signals going from the beaglebone black to the OLED screen.
They seem to be the reason of that behaviour. I removed them and it is correctly working (3 hours run, right now).
I do not understand why just 10 ohm can cause such a strange behaviour (do you have any idea)?
By the way, now it is working.
Thanks again for all your effort.
Regards

a_power
 
Posts: 13
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Re: OLED diplay misalignment with Beaglebone Black

by culebra on Wed May 09, 2018 1:56 am

I have the strong suspicion, from the description you provided, that you have signal integrity (dirty signal) issues on your SPI connection.

There may be ground level differences between the BBB and the OLED, it can also be the cables you are using. Removing the series terminations (the name for the resistors you removed) improved the speed of change of the SPI signals and fix the problem in your case. Without an oscilloscope, is hard to tell how close are you still have it malfunctioning.

Suggestion:

1. Make sure that the Ground (Return or whatever name you want to give it), one of the cables that feed power to the OLED is thick. Make also certain that the same reference connection between the OLED and the BBB is thick (16 to 18 AWG) .

2. Your cables for PWR should NOT be close to the signal cables, unless they are part of a cable assembly.

3. There are other more complex things to address, but without knowing if you have control over them, it would be confusing in your case.

Hope you find this helpful.

culebra

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