In any case, I bought one for three quid from eBay now available even cheaper on Amazon! The one that I bought is not integrated into a shield and so requires a little wiring...but it was cheap! SD Cards use SPI, or Serial Peripheral Interface, to communicate. This is provided on the Uno by pins 11, 12, and 13. On the Mega it will be 50, 51, and 52. The pin connections that are needed are shown below and by the included pictures:
|Function||Arduino Pins -
Uno / Mega
|GND||Ground||GND||Only one ground is needed|
|+3.3||Power on 3.3v system||+3.3||Only one power source is needed|
|+5||Power on a 5v system||+5|
|CS||Chip Select||10 or 53||This pin may wander while the lower three are confined to where the board puts SPI. Make sure your sketch reflects the right pin!|
|MOSI (sometimes called DO)||Master Output - Slave Input||12 or 50|
|SCK (sometimes call CLK)||System Clock||13 or 52|
|MISO (sometimes called I)||Master Input - Slave Output||11 or 51|
There is also a Card Detect pin on some cards (though not mine). It shorts to ground when a card is inserted. You should connect a pull up resistor (10K or so) and wire this to another pin if you want to detect when a card is inserted.
Screwshield Terminal Expansion Board for the Uno. The SD Card is pretty power hungry, as is the LCD, so we are connected to a wall power dongle. The breadboard in the foreground has a variable resistor as part of a voltage dividing circuit so I can vary my "readings" for test purposes.
In my next post I will talk about the software.