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.