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DFRobot 7 inch dsi screen fluctuating brightness

userHead ozcam 2023-04-10 04:02:59 880 Views2 Replies

I have connected a DFRobot 7-inch DSI touchscreen to my raspberry pi 4  all seems to work OK..but

the screen occasionally seems to fluctuate in brightness. ie for just a second the screen gets a little brighter or darker.

Anyone else have a similar issue..?

I also discovered that when the pi 4 is attached to the back of the screen, wifi becomes disabled or very patchy.. The raspberry pi 4 needs to be away from the back of the monitor

2025-06-19 15:59:51

Same here. 
 

The screen changes its brightness randomly and every ~20-30 seconds from (lets say it is set to 50), will shift to 55%, then 50%, then 45%, then 50% again. The only way for the brightness not to shift was to set the brightness to minimum (via the potentiometer at the top of the screen).
The pattern of the brightness shift is:
-20-30 seconds brightness is at (say 50%).
-Brightness increases ~55%, stays there for ~300ms 
-Brightness decreases ~50%, stays there for ~300ms.
-Brightness decreases ~45%, stays there for ~300ms.
-Brightness increases ~55%, stays there for ~300ms.
-Brightness finally goes back to 50% and stays there for 20-30 seconds before this cycle repeats.

The brightness shift is relatively hard to notice and can not be captured by a simple phone's camera, therefore we can not send you a video of the issue. But since we design the device to be sold as a professional-graded medical device, we would like to try and fix it.

What we tried:
-We tried moving the potentiometer that configures the brightness to various positions, in case the ADC sensing of the potentiometer was reading a value between two brightness positions. We only managed to find out that the minimum brightness position is the only position the brightness wont shift.
-We probed the 3.3V coming in to the display and we placed a decoupling ceramic capacitor, reducing some ripple we saw (from 300mVpp to 200mVpp), this did not change anything. We did the same for the voltage around/close to the potentiometer. We saw some ripple (~200mVpp), placed a filtering capacitor and reduced the ripple a little bit, but nothing changed in the brightness-shifting behavior.

The connection between the raspberry and the screen is via:
DSI Flexible Cable for RPi 5 - 300mm. SKU: 31-00025943
3671 as mid-connector
FFC / FPC Jumper Cable 15P 200mm length 686715200001
 

We would like to know:
-Is this a known issue? Have you noticed this brightness shift happen before?
-Is the brightness of the screen controlled by the screen itself or the raspberry pi also has some control over it?
-How could we further debug this or provide you more information to debug this behavior?

Thank you!

userHeadPic Vasilis.Christianidis
2023-04-10 17:45:33

I used my 7-inch DSI screen, but there was no brightness or darkness and the Raspberry Pi's WiFi worked fine!

userHeadPic Miya.zhang