Check out this great Raspberry Pi oscilloscope project from the Adafruit Forums:
Here’s my current RPi project — I’ve written some code to convert bitmaps to audio, for the purposes of playing it against an XY oscilloscope. With this method, I can turn any ancient oscilloscope into a clock, or, as you can see, something more.
Took about a week to write the code to manipulate the images you’re seeing. Performed on a stock Raspberry Pi, with the audio connector plugged into a 1974 Tektronix Analog Storage Oscilloscope.