EZ Expander - add digital output pins to Arduino

The EZ-Expander is an Arduino shield that makes it easy and inexpensive to add digital output pins to your Arduino. This is accomplished by utilizing two 74HC595 shift registers. There are 16 new output pins on the shield (numbered 20-35), and the shield itself uses 3 existing Arduino pins to operate (pins 8, 12, and 13), so overall you get 13 additional output pins to use. I’ve provided an open source software library that makes it extremely easy to access the new pins 20-35 without having to worry about controlling the shift registers in your Arduino sketch.

The new digital pins 20-35 can only be used for output, not input. They cannot source or sink as much current as normal Arduino pins. An Arduino pin can source/sink 40mA, but the outputs the EZ-Expander shield can only source/sink 6mA (ok, I’ve done more without damage). This is still enough to light an LED with an appropriately sized resistor to limit the current (e.g. 470 ohms), and, of course, you can use transistors to drive higher loads.

All other Arduino pins are brought up to the top of the shield for easy access. Since pins 8 (latch), 12 (clock), and 13 (data) are used by the shield, they are not available for use and are marked with an ‘X’ on the silkscreen.