LCD blanking out over time

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1

I’m working on a project where a microcontroller sends text to an LCD display. The screen is updated twice per minute. It runs fine for a while (sometimes 30 min, sometimes multiple hours) before messing up. My first iteration used an LCD from Adafruit which would display garbled text when the issue arose. That is the setup my attached schematic is for.

Next I tried switching LCDs and came across the 3.3v Sparkfun version. This allowed me to eliminate the buck converter as this LCD can be powered straight from the MPU. With this LCD the screen still messes up, but now goes completely blank instead of showing garbled characters.

I have noticed that the screen is likely to mess up when plugging in or unplugging the wall wart which keeps the backup battery topped up. I have tried putting a few different capacitors across the LCD supply and voltage lines, but that didn’t stop the issue.

Yesterday I got the logic analyzer and its looking like the LCD might be getting weird instructions due to the spike?

Any tips or advice would be greatly appreciated!

Schematic.jpg
Schematic.jpg960×720 45.9 KB

2

looking like the LCD might be getting weird instructions due to the spike

Yes, that’s my thought too. You might try a 0.1uF cap and a 100 to 1000uF cap in parallel at the LCD and a possibly on the input and output of your DC to DC converter to see if that helps.

3

I had tried a few across VSS and VDD like I’ve seen many places online, but that didn’t seem to help. Here is a screenshot from the analyzer:

https://i.imgur.com/oQa8BMM.jpg

D0 is enable

D3 is register select

The rest are the 4 bit data lines

4

I’m afraid I don’t have a solution, you’re going to have to experiment with different capacitors in different places to fix this. Maybe a different battery charger would help.

5

Ok, Thannks