This Micro SD card adaptor allows you to easily use gigabytes of flash memory with Teensy. It can also be used on a breadboard, or with almost any AVR processor.
A 3.3 volt regulator and 5 to 3.3 volt buffer chip protects the SD card, and allows interfacing to 5 volt processors
The SD adaptor can be used on Teensy++, with 4 pins and 2 wires.
The very first thing to do is solder the 3V pads on the bottom of the MicroSD adapter.
Then you need to wire it up in the following manner
+5V goes to 3.3V (100 mA max)
Teensyduino supports SD cards for USB communication. Select it from the Tools->USB Type menu after installing.
Several Arduino libraries support access to SD cards.
The SdFat library has been tested and is known to work on Teensy 2.0 and Teensy++ 2.0 with this SD adaptor.
Switch (SW) Pin
The flash socket has a switch that can detect when a card is inserted. Normally SW is not used. Most projects don't need this pin, and nearly all SD libraries just check for the card by communicating with it rather than requiring an extra pin.
But if you design your code for a switch, or use someone else's code that requires a switch, the option is there. The switch connects to an an unpopulated resistor, so a low-value resistor or jumper wire needs to be soldered in place to enable access to the switch.
The switch might also be useful in special cases, like perhaps a battery powered project that waits for a card to be inserted. The pin change interrupts can wake the processor from a deep sleep mode, which would save battery life compared to regularly polling to see if a card has appeared.