That’s kinda mean. The Arduino already has a socket and a board. Just the ATMega328 is 5,65 euro. For 21 IO pins, that’s 0.26 euro per IO. The MCP23S08 is 1,32 euro, so 0.17 euro per IO.

Browse around eBay for an original Altair 8800 and you quickly find that the price range is in the thousands of dollars. If you are a collector and have some money in your pocket maybe that’s… ...

Using an Arduino Development board and Max/MSP a handy four button MIDI controller has been created that is capable of counting from 1 to 15 using only ...

IO Extension – The FPGA board presented here features 49 GPIOs, all usable for IO extension with an easy to use library, on Arduino, Raspberry and on your PC.