I'm looking a little into using an rtlsdr as a software oscilloscope. It has a higher samplerate than the nano, and I like to imagine one could use the radio tuner to infer the square wave corners and make a ghz logic analyser for clean signals.

Reddit implies 0.3V - 1.8V are good maximum voltages to think about. Probably stay safer near the 0.3V bound on the lower end. So maybe >10x voltage drop from 3.3V.

I could also work with the signal within the working range of the oscilloscope, and modify the software to output a signal that is easier to log (by adding delays).

I tried to update the firmware of the dso nano oscilloscope, but my system didn't recognise the device, keeping giving usb errors (this is the raspberry pi, not the olimex serial client the programmer is plugged into). Trying with a different micro usb cable would be the next step for that.