EDIT: This Instructable has won Second prize in the 2013 Radio Shack Microcontroller Contest. Thank You to all who voted!
EDIT2: An Open Enigma with fake Standup Nixie Tubes like the ones pictured in this Instructable is currently available as a Special Kickstarter Edition:
This is our very first Instructable and this step by step guide will show you how to build a fully functional electronic replica of the world famous German Enigma machine. This Arduino based Open Source project is able to encrypt & decrypt any Enigma M4 encoded message.
This first ever fully functional Open Source Enigma "exact " Replica was inspired by the Kid's Game to Arduino Enigma Machine by sketchsk3tch.
Using Charlie-plexing Multiplexing for the LEDs, this circuit with 115 light emitting diodes uses only 38 pins and the 36 push buttons use only 4 pins total thanks to properly placed resistors (and the P-Channel MOSFETs) in the keyboard loop. These 4 16-Segment displays & an LED for each keyboard button would add up quickly the total number of pins required and even the Arduino Mega would have ran out of pins without the 2 methods mentioned above....
In response to the overwhelming demand, we designed the PCB and made it available through www.stgeotronics.com. Skip to Step 10 & beyond for more info. We also offer it as a complete electronics kit & an assembled & tested complete product.