This Jumperless V5 app scans each row, determines whether it's floating (vs tied to GND) by twiddling pull ups and pull downs, and prints it over serial.
This is the absolute slowest way to do it by writing to the filesystem every time, but it's meant to be an example app showing how to make connections and "properly". If you hard-code the routing, it can scan the whole board ~300 times per second (that's how the probe was sensed on the OG Jumperless.)
https://www.crowdsupply.com/architeuthis-flux/jumperless-v5
