Strange GPIO-Signals on BBB

I am running two BBBs via power adapter, and I wanted to test the GPIO pins. One of them runs still on the manufacturing OS, the other one is up-to-date. Now I wanted to see the GPIO pin values with an oscilloscope. While trying to switch the pins on and off on the up-to-date-board via echo on/off > I experienced that the pin I wanted to switch never changed state. Therefore I tried to do the same on the other board, thinking that it was a software fault. But there I only measured a 50Hz-triangular signal, regardless which pin I chose (Even on GND and 5V). Why? What can I do to bring both of them back to work?

Sounds like you have a grounding issue with your scope. Make sure the power and scope are connected to the same power outlet that the scope probe ground is connected to the board ground.


Both are connected to the same power outlet.
And why is the other BBB not reacting when changing the state? It always stays at 1 (3.3V) even if I switch it off via command line…

Sounds like the pin mode is not set correctly.There are multiple registers that need to be set. Setting up the pin mode and then setting up the pin mux to make sure the pin is connected to the actual pin on the processor…


Hello Maxi,

you could use libpruio for this test. It should work on both operating systems and the pin configuration can be done at run-time (requirements: universal overlay libpruio-00A0.dtbo and admin privileges). Furthermore it’s much faster than the sysfs.