Problem finding pin assignment on atmega2560 for sd card without shield.

Hi guys, I’m having trouble finding the pin assignments on a SD card to connect to atmega2560 rev3. What im really trying to do is play wave files off a sd card then using a speaker to output the sound.

The idea comes from this:

i just dont know the pin assignments for sd card to arduino, thanks in advance.

SD cards use SPI interface - on a mega that is pins 50-51-52-53 I believe. You can find them on the mega schematic in the Products page.

3.3v goes to 3.3v on the Arduino
GND goes to Ground on Arduino
D0 goes to pin 51 on Arduino
D1 goes to pin 50 on Arduino
CLK goes to pin 53 on Arduino
D3 goes to pin ?? on Arduino ????????

still unsure...