Last night Scouts had a “Problem Solving” night. Their mission over the night was to defuse a bomb by cutting the coloured wires in the correct order. They would receive the clues needed to defuse the bomb by completing puzzles and tasks. Two of the clues required decoding.
I had a fedora and a nice long coat, which I’d worn recently at a 20’s themed party as “Press Photographer”. I put it to use over my Scout uniform as “Detective”.
Creating the “bomb”
The first prototype was created in a cafe while listening to my children play carols with their local brass band outside. This breadboard prototype had just the wires to disconnect and demonstrated the game logic.
I had tried asking Gemini to produce code. It completely failed, especially on the Morse Code task. It was quicker and more reliable to code by hand. The final code is available as a Git-Hub Gist.
Setting Up The Game
I chose the following sequence for my solution:
White, Green, Red, Yellow, Black
The Scouts were given an initial scene setting message in the form of a telegram message, then as they completed tasks over the evening more “telegrams” were received. There is a little redundancy in the clues allowing Clue 2 to be skipped (so if they fail a task we arrange for that one to be left out). The clues were:
...RED IS ONE OF THE LAST THREE TO BE CUT...
...BLACK IS CUT LATER THAN RED...
...THE LAST TWO ARE THE COLOURS OF A WASP...
...GJB JVERF NER PHG ORGJRRA JUVR NAQ LRYYBJ...
This is a Ceaser Cipher message using ROT-13. One of my younger Scouts immediately recognised it and announced this quite loudly so that the other teams also knew where to look. I had a code wheel laying in my box of bits and this was quickly found. He then spent some time trying the different combinations to work out the rotation used. I did suggest looking at double letters in the message and thinking of what words with double letters were likely to be seen. The Ceaser Cipher clue was a success.
The text is “Two wires are cut between white and yellow”.
...LOOK CAREFULLY AT THE BOMB...
The larger LEDs on the board were given a random pulse rate and flashed at approximately that rate. The Pico’s own LED flashed the following in Morse Code: “White comes before green”.
This took a little while to spot. I wonder if it would have been seen quicker if I hadn’t have fitted the other LEDs. We’d studied Morse as part of the Communicator Badge the week before, and my box of bits happened to have a few of the Morse instruction sheets left over from that session.
All of the clues, without the Morse clue, lead to two possibilities: “WGRYB” or “GWRBY“. One team successfuly came to this conclusion, but failed to copy the Morse message correctly. (They had DEFO GREEN not BEFORE GREEN). They tried to guess and defused the bomb on their second attempt.
Learning for next time
The game was a great success, with excellent feedback afterwards.
My Morse clue was needed to resolve two possible answers, but the Scouts learned which was which immediately. Next time I’d make the ambiguity come later in the solution so that the Scouts would go further and the tension would increase before finding out if they were correct.
I intended the Scouts to cut the wires to give part of that traditional movie bomb defusing experience. I tested last minute in the kitchen and found that the cutting action was too electrically noisy and caused bouncing in the inputs. I’ve since changed the code to increase debouncing in the switches, tolerate the state moving back and forth between valid states, and add pauses in the win and lose routines to really allow signals to settle. We ended up unplugging the wires rather than cutting them, so it still worked.
Other articles in this series
Technical Deep Dive on the Bomb Puzzle
Discussion of the code and design of the system
Scouts “Defuse The Bomb” game – Shallow Dive
Introduction for someone without electronics experience wanting to build this, perhaps for Scouts Digital Maker Badge.
Leave a Reply