This is the SparkFun VKey Voltage Keypad, a simple board that adds a keypad to your microcontroller project without using multiple I/O pins. This keypad has 12 pushbutton switches in a 3×4 array. The VKey operates by outputing an analog voltage to encode which key has been pressed, which can be read by an analog to digital converter on a microcontroller on a single input pin.
Traditional digital keypad interfacing techniques can require a large number of digital I/O lines. On a small controller, there may not be many I/O pins left for other tasks. The VKey operates at a voltage of 3.3-5.5V and features a dual opamp which is used as a current source and buffer amplifier.
Note: The SparkFun VKey Voltage Keypad comes with the surface mount components assembled, but the PTH tactile switches are loose, and will need to be soldered to the board. Check the Hookup Guide in the Documents section below for assembly instructions.