The Binary Keypad
The Binary Keypad has the only keys a true hacker needs--0 and 1. :)
Okay, so what do you use it for?
Its main purpose is to send data to a shift register, LED driver, or other serial-input circuit without having to wire up and program a microcontroller. or use a fancy-shmancy Bus Pirate.
The keypad has 3 outputs: clock, data, and latch. Pressing the 0 key pulses the clock line high while keeping the data line low. Pressing the 1 key pulses the clock line high while bringing the data line high.
The third button controls the latch output. The small switch to its right determines if the latch output is active-high or active-low. For example, with the switch up, the latch output line is high when the third button is pressed, and low when it's not. The active high/low switch allows you to connect the third button to pretty much any logic input.
Plus, there's something aesthetically/conceptually pleasing about a keyboard with only 0 and 1 keys.
The circuit is quite simple, as you can see below; three Schmitt triggers are used for switch debouncing and two XOR gates compute the output states.
Here is a video of the Binary Keypad driving two nixie tubes with a kit from ogi lumen:
photosPhoto gallery is on Flickr.
(click to enlarge)