A 4$, 4ICs, Z80 homemade computer on breadboard

This is the Z80-MBC (Mobile Breadboard Computer), a mini 4MHz Z80 64kB RAM system with a Basic interpreter and that can be easily expanded. It has an “Arduino heart” using an Atmega32A as an “universal” I/O emulator. And can be used and powered with a tablet or smartphone too… During some surfing on Ebay I realized that with 4$ it is possible to buy enough ICs to build a complete Z80 system that can be done using a breadboard. So I did it and here it is the story!”