Percent Composition Puzzle

I mentioned in my introduction post that I've made a puzzle that I plan on using for my chemistry classes. This puzzle requires the student to determine the empirical formula from the percent composition of each element. The puzzle is in the form of a box with a sliding door, a control panel, and an On/Off switch. Insider are an Arduino Nano, a buck converter (with 9V battery), an LCD screen, a momentary switch button, a rotary encoder, a servo motor, and a RC522 RFID reader. I designed the box in Fusion 360 and printed out the parts on my Prusa Mk3 printer.

When the device is turned on, a default puzzle with an (relatively) easy solution is given. This on has a solution of C2H5NO.

The rotary encoder (the adjust knob) is used to change the value of each element. Pushing the rotary encoder button toggles between each element. Once the student is confident that they have the answer, they use the test button to attempt to open the lock (a 9g servo motor). A correct answer gives them an affirmative message and a satisfying swish sound from the servo motor. They can then slide the door on top open and see what's inside.

 The cool part is that you can update the puzzle with a new problem by scanning a programed RFID card, which changes the screen and the variables in memory for the correct answer. The programming of this took a while and was very educational for me. Here's a card with a much more challenging problem programmed into the RFID memory.

 The data is easy to program onto the cards. There's even an Android app you can use to copy the data onto the card. Here's what the ASCII data on the card looks like.

I'm pleased with how well it worked out and learned how to integrate several of the components thanks to DroneBot Workshop videos. I'm going to post the code for the Arduino (if anyone wants to see what I did) as a reply to this post because it is quite long.