Starting small with a PLAN is good. A rough schematic sketch freehand is a good idea no matter what. Just sorta randomly plugging in wires is NOT a recipe for success! LOL
I was not "randomly plugging in wires". I was following this pinout (specifically, page 2), and used this article to match the alternate label names.
@robert_sydes
Please clarify the situation -you returned the cards back and do not intent to continue researching the problem with another ones, right?
So you can close the topic and forget about it ...
Unless I run into the same problem with the new ones (I don't have them yet; this time I'm going to try them out immediately, as soon as they arrive (in a day or two)), then yes, that is correct.
Of course (??) you'll format them before doing anything else.
I am having the same problem(s) with the new cards. Perhaps it's actually problem with the card reader modules (pack of 5, tried them all)? What tests could I perform to check if they are functional?
Format them as DOS FAT on your PC and copy a couple of small files to it. something simple, an ASCII .txt file with an 8.3 file name. Make a test prog that appends to that file in void setup() so it runs once after reset. Read the file on the PC and see if it worked. Use a SD 32gb or less.
I mentioned formatting them. They have to be formatted.
No Replies, just a litany of complaints and frustrations.
"Getting help" involves joining in a conversation. Do you see yourself as open to having a conversation?
I did try formatting them.
What do you mean I haven't replied to anyone? (Unless I'm doing that wrong. If I want to respond to a particular person's post, I am supposed to click the reply button immediately below it, right?)
see post 17
We still didn't see your code and your schematic.
Following your instructions, with a few differences*
Cards used (the new ones): link.
*Using the Read/Write example (vs. writing my own sketch from scratch). I changed if (!SD.begin(4)) { to if (!SD.begin(8)) {, as per the Uno WiFi rev 2 pinout. I also only created one text file (instead of a couple) named "test.txt". The contents of that file is the word "Blank".
The full sketch:
/*
SD card read/write
This example shows how to read and write data to and from an SD card file
The circuit:
SD card attached to SPI bus as follows:
** MOSI - pin 11
** MISO - pin 12
** CLK - pin 13
** CS - pin 4 (for MKRZero SD: SDCARD_SS_PIN)
created Nov 2010
by David A. Mellis
modified 9 Apr 2012
by Tom Igoe
This example code is in the public domain.
*/
#include <SPI.h>
#include <SD.h>
File myFile;
void setup() {
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for native USB port only
}
Serial.print("Initializing SD card...");
if (!SD.begin(8)) {
Serial.println("initialization failed!");
while (1);
}
Serial.println("initialization done.");
// open the file. note that only one file can be open at a time,
// so you have to close this one before opening another.
myFile = SD.open("test.txt", FILE_WRITE);
// if the file opened okay, write to it:
if (myFile) {
Serial.print("Writing to test.txt...");
myFile.println("testing 1, 2, 3.");
// close the file:
myFile.close();
Serial.println("done.");
} else {
// if the file didn't open, print an error:
Serial.println("error opening test.txt");
}
// re-open the file for reading:
myFile = SD.open("test.txt");
if (myFile) {
Serial.println("test.txt:");
// read from the file until there's nothing else in it:
while (myFile.available()) {
Serial.write(myFile.read());
}
// close the file:
myFile.close();
} else {
// if the file didn't open, print an error:
Serial.println("error opening test.txt");
}
}
void loop() {
// nothing happens after setup
}
The results
Output of serial monitor:
Initializing SD card...initialization failed!
I check the text file: the text file is unchanged.
The below is soooooo wrong. I know that you pulled it somewhere from the product page but it is still wrong.
On an Uno WifiRev2 the SPI pins are only available on the 6 pin header. See the schematic
Please show the picture of the SD reader front side
Thank you
Your module has level converter, so it can be safely connected to 5v boards
I tried both the 3.3V and 5V pins (on the Arduino); with the modules that I hadn't yet used (they came in a pack of 5), I tried the 3.3V pin first, so I think I can rule out overvoltage as the issue.
This module should be powered with 5v, it won't work with 3v3 power.
The Vcc pin of that SD module needs 5V, not 3.3V. Depending on how the Uno Wifi is powered, its 5V output may not provide enough current to power the module. But typically this kind of problem results from not having the physical connections match the software. Do you have a regular Uno or Nano or Pro Mini that you could test with? That would at least settle whether the module and cards are good.
I don't have any other Arduino models currently. The Uno R4 WiFi comes out in early July, and I'm considering buying it. Already, it seems to have a bit more documentation than the Uno WiFi Rev 2 (and is much cheaper 
).
