PM: 2.8" LCD board for the PM...

Author Message

Admin Group

Joined: 31/12/2012
Location: New Zealand
Posts: 9187
Posted: 10:55am 21 Oct 2022      

Quick update on this thing:

Built one, and tested all the major aspects of it, and it works fine.

One thing I did note, is that the PM SD card handler REALLY does not like the 1k series resistors on these LCD panels!
Reading from the card works fine, but any attempt to write or save to the card causes a low-level filesystem hard error(not verbatim - I forget EXACTLY how it was worded).

This error is bad enough, to totally corrupt the SD card, and you have to reformat the card to use it again.

I have heard of people having this issue before, when they use any modular type of SD card connection, that has anything at all in series with the SPI connections.
This is also the case here, so one thing that has to happen, is those 1k resistors need to be removed and replaced with zero-ohm ones or just wire links.  Once you do that, writing works just fine.

Interestingly, there are 1k resistors(R1,R2,R3) in series with SD_CS, SD_CLK and SD_MOSI, but there is no resistor in series with SD_MISO, so you end up with a kind of "Unbalanced" SPI bus.  This does not seem to bother Micromite series chips, but the RP2040 really does not like the taste of those series resistors, so they MUST be removed.  That will be true for pretty much ALL LCD modules where there are series resistors in the SD card SPI lines.