Arduino-based oscilloscope: attenuate the input by varying reference voltage?
I was thinking of this kind of op-amp input stage:







simulate this circuit &ndash; Schematic created using CircuitLab

SW1-3 here represent three GPIO pins of the µC which are then used to set the feedback voltage divisor.

To answer your question:


  By changing the AREF voltage I can change the full range voltage of
  the DAC. Will this produce the effect of giving me lower V/div without
  losing resulotion?


Yes, this will actually work as desired. But you'll have to be careful because the ADC may be destroyed if it sees an input voltage that's higher than V(AREF), even if it's still far below Vcc.


  For higher V/div, would a simple single digital pot work?


Not sure about that. Depending on the signal's source impedance the additional load of the voltage divider may degrade/distort the signal. Also, check the potentiometer's transfer characteristics for different frequencies; and have you thought about AC signals which may go below GND?