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I was having a problem making my sd card reader work with Arduino Mega, I tried a lot of things to no avail until I read somewhere that I should try putting a 10k or 1k resistor in series with the MOSI and SCLK pins but for some reason in my case I had to put a 1k resistor in series with SCLK and CS pins to make it work. What exactly is the reasoning ?

Waveshare microsd card reader:

SD card reader schematic

Out of curiosity I added a level shifter too since the sd card module doesn't have one on it and that didn't work, so the Arduino and sd card reader pins must be connected to each other with no level shifting !

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    \$\begingroup\$ Is your Arduino a 3.3V one, or a 5V one? Your resistors aren't in series, they are pull-ups. I can understand this for the CS pin, but it's curious that you would need a pull-up on the SCLK unless it's configured wrong. Are you bit-banging the SPI or using hardware SPI? \$\endgroup\$ – Ron Beyer Mar 20 '20 at 2:11
  • \$\begingroup\$ It's 5V and I'm using the hardware SPI and I'm running the Arduino IDE SD example sketch. \$\endgroup\$ – BigRedMachine Mar 20 '20 at 16:08

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