Arduino Oscilloscope

• A poor man's oscilloscope is an Arduino connected via USB to a computer which uses a Processing code running on your computer - https://www.build-electronic-circuits.com/arduino-oscilloscope/
• Using a Complex Programmable Logic Device (like FPGA but simpler) Arduino shield - [1]
• From scratch by a physics guy - not complete - [2]
• Using Processing with good visual interface, 4 channel - [3]