Micro-SD breakout] [Connection to MEGAI am having quite a bit of trouble trying to get my Arduino MEGA 2560 to read my micro-SD card. My wiring is as follows:

Breakout    Arduino
5v            5v
Gnd           Gnd
CLK           52
DO            50
DI            51
CS            53
CD            Was not connected and then connected to 47 (neither worked)

Here is my code:

#include <Wire.h> //library necessary to use I2C communications bus
#include <Adafruit_Sensor.h>
#include <Adafruit_BME680.h>
#include <SD.h>
#include <SPI.h>

const uint8_t chipSelect = 53; //chipSelect pin for the SD card Reader
const uint8_t cardDetect = 47;

File CO2Data; //Data object you will write your sensor data to

void setup() {
Serial.begin(115200);//"begins" the serial monitor so you can print stuff out when connected to the computer (set baud rate to 115200)
Wire.begin ();//begins the I2C communications bus so it can talk to the K33

Serial.print("Initializing SD car...");
pinMode(53, OUTPUT); 

if (!SD.begin(chipSelect)) {
Serial.println("Card failed, or not present");
// don't do anything more:
while (1) ;
Serial.println("card initialized.");
File CO2data = SD.open("datalog.txt", FILE_WRITE);
if (! CO2data) {
Serial.println("error opening datalog.txt");
// Wait forever since we cant write data
 while (1) ;

The SD card is formatted to FAT32.

Thank you for any help!

  • try the CardInfo example
    – Juraj
    Jun 10, 2019 at 18:48
  • I did try to cardinfo example and came up with the following message:Initializing SD card...initialization failed. Things to check: * is a card inserted? * is your wiring correct? * did you change the chipSelect pin to match your shield or module?
    – CMil
    Jun 10, 2019 at 19:28
  • Update: I set chipselect to 10 in the Cardinfo example and card is found and present. However, it still won't run in my sketch. I have gone through trying different pin combinations.
    – CMil
    Jun 10, 2019 at 21:54
  • do you have some shield on the Mega or some other devices wired to it?
    – Juraj
    Jun 11, 2019 at 14:15
  • I do, I have a couple of things wired to the MEGA: Adafruit BME680 (temp pressure) using the I2C interface (SCL wired to 21 and SDA wired to 20) and a KC-30 CO2 sensor wired to pins 10 and 9.
    – CMil
    Jun 11, 2019 at 21:45

1 Answer 1


The non-analog ground line attached to the micro-SD was pulling down my voltage. Just hardwired to different ground and problem solved! (Check your voltages).

From what I could gather. the ground pin on the MEGA inline with the digital pins was a different ground source (digital ground). I literally took the ground lead from the SD board and just touched it to the housing of the USB connector on the MEGA and my voltage came back.

  • It's OK to accept your own answer as the solution to the problem.
    – VE7JRO
    Aug 6, 2020 at 0:08

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