A CHEAP OSCILLOSCOPE FOR ANYONE WITH A LAPTOP AND AN ARDUINO. Uses only 7 lines of code and the latest arduino software.
https://www.build-electronic-circuit...scope-updated/

The code basically sets up an input and sends it to the serial laptop cable. Use the new "serial plotter" tool in the software to graph the output.
DO NOT EXCEED 5V AT THE INPUT PINS. Use a voltage divider if going above 5v. I suggest a 5v zener diode across the pins for safety against spikes.
There. Now everyone can give us screenshots. ha.