The original idea behind this project is to develop a keyboard. So I prepare this first try with wires. At first, it is easy, it only has 3x6 buttons

We connected it to an esp32 with a lipo battery and use a 3D printed case.

We use 3 IO Pins to output a voltage, one pin at a time, and look for the voltage in the other 6 pins to detect the key pressed. It only works if we press one key at any time, but for a calculator is enough.

The calculator is programmed in micropython, using the eval function to evaluate the math formulas we introduce. We have created even a small graphic plotting of the function.

But when we increase the number of keys .... using wires to connect the buttons is a mess that we can't resolve ... so we will go the PCB way :-D