Here are some photos and videos of early proofs of concept to make sure you could actually use a crosspoint switch to make a reasonable stand-in for a physical jumper. I was expecting this not to work, but surprisingly, it did.
Here's the 555 test setup. I'm using a DIP version of the MT8816 which was really handy for this early testing stuff.
and here it is working here's the code for this
What I'm doing here is using the crosspoint switch to change the resistors and capacitors in the 555 circuit to change the frequency.
That other 8 pin chip on the left is a charge pump to make the -9v power rail.
Then I realized I should probably do something more intuitive for the students so I set this up with LEDs