When electricity travels through one rotor it changes the letter once. But remember, we have three of these rotors and they each have different wirings on the inside. When electricity travels through all three of them it changes the letter three times.

Then at the end, we have the reflector. This also has 26 metal contacts. Inside is more wiring that connects the letters in pairs. So it goes in as one letter and then comes out as another letter.

To the right of here is the input wheel. It has 26 wires that go in and connects to the 26 metal contacts.

Let’s put this all together. Electricity flows through one of the 26 wires, let’s say the wire for the letter Y. Then it gets changed to a different letter at all three rotors. Then it hits the reflector, which again, changes the letter. And then it goes back through the rotors again which changes the letter three more times. And it comes back out on a wire that represents a completely different letter. And if you were counting, this means the letter was changed seven times.

The idea here wasn’t to make the smallest one possible. I decided to make a device that was practical and useable. And something that looks like it was from WW2. Something that could actually be used in the field in place of a real Enigma machine. Obviously there were some limitations. I could have a 26 key keyboard for a start so I had to come up with a UI that would work with a minimal number of keys. I bought a small 128x64 OLED, a suitable battery and started breadboarding it all up. With it working on a normal Arduino I bought an Arduino Pro Mini (or a good replica!) and started looking at getting it running on that.