As I mentioned before, best way to know new part is to build some project based on that. After traveling with my family some time age, I had an idea to build digital safe toy for my son. He had some with the real thing, so I figured this could be a good toy at home.

It doesn't have to be big and heavy, but it should have

- password entry using keypad

- LCD screen, symbol display controlled via I2C expander makes perfect sense here

- Buzzer and LED blinker clearly

- Li-Po Battery powered. Charging can be external

I started to look around for firmware, and immediately found Arduino Electronic Safe. I added RGB LED and buzzer support, which forced me to rewrite most of the code to run async.

One trick I use for prototyping is a "poor man's 3D printing" made of thick cardboard left after furniture deliveries.It is easy to cut and shape with paper knife. Final result is a bit bulky, but looks neat and strong.

It is not very strong though, so I cover front with the plexi-glass panel. It is easy to cut using soldering iron and aluminum ruler, and bend using heatgun.