My latest project is to build a giant working calculator out of Lego. This is by far the most ambitious project I’ve taken on, and I’ll be blogging about my progress over the coming months. Why do I call it a ‘giant’ calculator? Because it’s going to be BIG! I estimate it’s at least one metre per side, if not larger.

Why a calculator?

I saw a video online of a 7 segment display made out of Lego. It had a wonderfully simple mechanism, and was hypnotic to watch in action. As I watched I realised that I could put the 7-segment display to good use, and build a calculator!

What’s a 7 segment display you ask? It’s a display device commonly used in simple calculators, where 7 individual segments are used to make digits from 0 to 9, and even some simple capital letters.


Mechanical 7 segment displays

Most of the existing designs for Lego 7 segment displays use a sequential counting mechanism, typically using a barrel rotating to toggle each segment changing. This type of design is fun to watch, but can only count sequentially from 0 to 9 and back to 0 again. See this picture for an example of a barrel mechanism; very ingenious in its own way.


Source aeh brickshelf

This design is ingenious, but doesn’t lend itself to a calculator display which needs to update quickly each time a key is pressed. I set my mind to devising a better way to update the digits, one that was fast enough to be used as practical display.

I also wanted to have a full calculator keyboard, so people could press the keys, see (and hear) the display update in real time, and do useful calculations.

My Goals

  • 8 full-size digits, with decimal points
  • Working keyboard with basic operators, memory, and some advanced maths functions
  • Keys are large enough that they can be pressed by hand
  • Calculator actually works and can do arithmetic
  • Display is fast to update once a key is pressed.
  • Uses only official Lego parts; no Arduino or third-party sensors.
  • Big! I want it to be visually impressive and fun to use!

Over the next few months I’ll be blogging my progress on this project. I’ve been working on prototypes for the display digits and keyboard, trying out lots of ideas and throwing them away almost as fast. It’s a very iterative process of discovery!