There is a popular Chinese-made 3.5", 480x320 TFT LCD shield mentioned, for example, here:
It can be seen on the picture above that the SPI traces from the upper-left header go directly to the microSD-connector contacts. If used with an Android UNO, these traces will apply 5V signals to the card, possibly destroying it.
It seems no SD card may be used in this arrangement, am I correct?
It's not a shield, at least I don't think it is. Not in the Arduino meaning of the word. You couldn't plug it on top of an Uno or Mega, I suspect.
Can you post a link to this item? Hopefully there is a schematic available to tell us that's connected to what.
I have to say the design looks very suspect. Don't know what U2 and U3 are, but I don't see any bypass caps for them. And the regulator chip has no caps either...
Certainly no SD card can be used in that arrangement with a 5V board safely. People do attempt to use it with them though, with varying degrees of success. And as @PaulRB has already noted, it's severely deficient in the capacitor department.
There is a link in my first sentence. It is a shield, and it sits on the top of Uno. And, unfortunately, I am not aware of the existence of any documentation on this product.
For documentation, try 3.5inch Arduino Display-UNO
Thank you. I am just puzzled by the fact that people actively deal with this SD port and seem happy -- see, for example, this: Creatively using text-files with an SD Card on a 3.5 inch TFT LCD Display and Arduino (Part 3 of 6).
Yes, but it's a link to another topic on this forum. The links on that topic are dead. So no way to find a schematic for the PCB. I hoped you would post a link to where you purchased it, and there would be a schematic there (and I might win the lottery this week).
Apologies. But as you rightly pointed out, if you did try to use the SD card on a 5V Uno or Mega, you could damage the card.
As I said, varying degrees of success. Operating parts outside of their Absolute Maximum Ratings doesn't mean that the part will die immediately. You may get away with it for quite some time. You may get really lucky and never see a problem in your use case. Or, you could have oddball, impossible to track down problems that crop up elsewhere but are caused by abusing the SD card. Or, it could just die right away. There's no telling.
People very often fail to recognize the difference between "I've always gotten away with this" and what the manufacturer guarantees will work in all instances.
