I’m having problems with 2 different mcufriend 3.5” display shields from 2 different vendors on mega 2560 boards, but not unos. The displays power up but have white flickering lines and snow. The displays will show the correct images briefly (but hard to see for the flickering and snow). This happens regardless of sketch being run on the 2560s. They function properly on unos. I’m using the mcufriend and adafruit gfx libraries. What gives?
Hi ...
Send a link/picture of your shields products here
Maybe there is power problem with your Mega2560,
some of the low qualities of Mega2560 boards and maybe DIY pcb's have this problem
(i make a DIY pcb before the first version have a flickering nose with lcds)
Check your 5v regulator maximum current (on Mega2560) ?
If your shields haven't AMS1117 3.3v its better to solder one manually !
Marteen ,
You may be on to something. I powered up the board using a half dead 9v battery and the display worked just fine at about 3.1v vs 5v. The mega board has a ams1117 already installed, board voltage measures 5.04v and 3.3v at the 3.3v pin. Not sure about the current that the display is drawing. It’s not really feasible to measure on a shield. Is the display shield itself supposed to have a voltage regulator?
mswartz:
Is the display shield itself supposed to have a voltage regulator?
Yes, some of Blue Solder Masked lcd's have a ams1117 3.3v, and this shields works better
you can add ams1117 3.3v like this photos, (this is a 2.4" tft lcd)
Marteen, thanks for the pictures. That is a very creative approach to the problem. I have a couple of the blue board type displays. Both have voltage regulators. None of the red ones do.
so still the problem not solved ? or ...
A neat way to provide a proper regulator on the shield.
All of these current Red mcufriend.com shields are WRONG. They omit the 3.3V regulator and rely on the wimpy 3.3V pin from Uno, Mega2560, ... which is only rated for 50mA.
I am not too worried about the 2.4 inch shields. The backlight current is not too big.
But the 3.5 inch shield backlights take > 100mA.
Most of the Red mcufriend.com shields contain 74HC245 buffers instead of 74LVC245.
The HC chips are not input voltage tolerant. i.e. they do not like 5V inputs when VCC = 3.3V
David.
I do believe that this will solve the problem. I will order some 3.3v ams1117’s.
Thanks for your help!
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