Problem with OLED and Gotek

HxC Floppy Emulator on Amiga support
tytan
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Re: Problem with OLED and Gotek

Post by tytan » Tue Jan 09, 2018 11:47 pm

Hello.
I have Gotek with HxC.
I have connected the same OLED as in this post. At the beginning, OLED did not light up.
After setting the start delay to 5, works well! (HXCFEUSB_V3_1_1_0a.UPD)
Thank you, good job,
tytan

Jeff
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Re: Problem with OLED and Gotek

Post by Jeff » Wed Jan 10, 2018 1:27 am

tytan wrote:
Tue Jan 09, 2018 11:47 pm
Hello.
I have Gotek with HxC.
I have connected the same OLED as in this post. At the beginning, OLED did not light up.
After setting the start delay to 5, works well! (HXCFEUSB_V3_1_1_0a.UPD)
Thank you, good job,
tytan
Well i would prefer to avoid this option... Will received one of these screen this week. Hope to understand why they are working so bad...
(PS : Same issue there : http://torlus.com/floppy/forum/viewtopi ... =33&t=3258)

tytan
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Re: Problem with OLED and Gotek

Post by tytan » Wed Jan 10, 2018 6:51 pm

Measurement showed that this OLED does not have a pull up.
Does an ohmmeter: between + and SDA or SCL should show values around a few Kohms?
tytan

Jeff
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Re: Problem with OLED and Gotek

Post by Jeff » Wed Jan 10, 2018 10:34 pm

tytan wrote:
Wed Jan 10, 2018 6:51 pm
Measurement showed that this OLED does not have a pull up.
Does an ohmmeter: between + and SDA or SCL should show values around a few Kohms?
tytan
I think that there is a LDO voltage regulator. To measure the pull up you must use the output pin of this LDO.

tytan
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Re: Problem with OLED and Gotek

Post by tytan » Sat Jan 13, 2018 8:48 pm

You're right.
There is 662K.
I have measured - they are pull up.

I use a few days with a delay of 5, OLED works correctly - always starts.

Jeff
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Re: Problem with OLED and Gotek

Post by Jeff » Sat Jan 13, 2018 9:37 pm

tytan wrote:
Sat Jan 13, 2018 8:48 pm
You're right.
There is 662K.
I have measured - they are pull up.

I use a few days with a delay of 5, OLED works correctly - always starts.
662K ? Very high value for pull-up...

btw i have just have received one of these screen. i will try to check this tomorrow.

tytan
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Re: Problem with OLED and Gotek

Post by tytan » Sat Jan 13, 2018 10:02 pm

662K it's stabilizer ;) https://www.mysensors.org/uploads/57c1a ... e/662K.png
pull ups 4.7k ohm

Jeff
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Re: Problem with OLED and Gotek

Post by Jeff » Sun Jan 14, 2018 2:57 pm

So i got time to have a closer look to this problem :

As expected the problem is the reset RC circuit. This screen have some curious RC part value which make the oled controller staying in reset a during a looonnnng time after the power up. The Reset RC circuit is done with C8 (4.7uF) & R3 (560K !!!!). Which give a time constant of 2.632 seconds. So no surprise here...

I have changed the resistor value to reduce a lot this time constant. ~4.7K ohms value seems to work reliably without any extra software delay :

First try :
diymorecc_patch1.jpg
diymorecc_patch1.jpg (63.4 KiB) Viewed 845 times
diymorecc_patch2.jpg
diymorecc_patch2.jpg (81.17 KiB) Viewed 845 times
The Fix :
oled_diymorecc_fix.jpg
oled_diymorecc_fix.jpg (208 KiB) Viewed 845 times

Jeff
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Re: Problem with OLED and Gotek

Post by Jeff » Sun Jan 21, 2018 12:13 pm

One more thing about these oled screens : it seems that they prefer to be powered with 5V instead of 3.3V : No more brightness variation and brighter display.

EDIT : IREF resistor mistake spotted ! Over current is possible, so avoid to use the 5V source !

tzok
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Re: Problem with OLED and Gotek

Post by tzok » Sat Jan 27, 2018 9:08 pm

"Myfriends" had messed up resistor values... as usual:
Image
According to this diagram there should be 3x4k7 and 1x560k resistor. And there is, but one of 4k7 resistors is swapped with a 560k resistor!?! To be more precise R3 (R4 on the diagram above) and R4 (R1 on the diagram above) are swapped.

I'd also like to notice, that SDA and SCL signals accept 3.3V TTL logic, and have internal pull-ups (to 3.3V rail) and definitely should not be pulled up to 5V rail. There is a LDO voltage regulator on the board, so the module can be powered from 5V Vcc.
Last edited by tzok on Sat Jan 27, 2018 9:53 pm, edited 1 time in total.

Jeff
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Re: Problem with OLED and Gotek

Post by Jeff » Sat Jan 27, 2018 9:51 pm

yes this is what i have suspected too, a silly mistake.
Btw the 4K7 resistor instead of the 560K on the IREF pin doesn't sound good at all according to the datasheet ! :?

tzok
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Re: Problem with OLED and Gotek

Post by tzok » Sat Jan 27, 2018 9:55 pm

Indeed... it doesn't foretell long life of that display. I've just verified that swapping these two resistors does solve the problem (and doesn't noticeably affect the display brightness).

https://youtu.be/__3InV5tdzM

Jeff
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Re: Problem with OLED and Gotek

Post by Jeff » Sat Jan 27, 2018 10:22 pm

The IREF mistake may explain the brightness change i can see with a 3.3V power source...
Unfortunately few of the buyers will be able to exchange these resistors. :?
i am wonder how many of these faulty devices are in the wild now... I lot regarding the numbers of feedback i got !

This doesn't sound good at all this story...

Jeff
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Re: Problem with OLED and Gotek

Post by Jeff » Sun Jan 28, 2018 1:05 am

ISEG = Contrast / 256 x IREF x scale factor
in which the contrast (0~255) is set by Set Contrast command 81h and the scale factor is 8 by default.

The magnitude of IREF is controlled by the value of resistor, which is connected between IREF pin and VSS as shown in
Figure 8-15. It is recommended to set IREF to 12.5 ± 2uA so as to achieve ISEG = 100uA at maximum contrast 255.

the voltage at IREF pin is VCC– 2.5V. (VCC = Panel driving voltage ~ 12V).

For sure with 4.7K these screens will have a short life...

DanielDOC
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Re: Problem with OLED and Gotek

Post by DanielDOC » Mon Jan 29, 2018 8:36 pm

Hello,

Today arrived my "diymore.cc" screen. Since can't do the "fix" today, how can I modify the "delay" on latest firmware 3.1.1.4a? I like to probe tonight the "Normal" vs "Indexed".

Thanks

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