How Can i Protect my Oscilloscope from high voltages?
Since your ADC is quite slow, you can probably provide a protection circuit without much difficulty. Something like







simulate this circuit &ndash; Schematic created using CircuitLab

In the event of an overvoltage, the diode will steer the current into the power supply or ground, while the resistor will limit the value of the current. For instance, if you're using a 5 volt power supply, and apply 100 volts to the input, the total current flow will be about 10 mA, while the diodes (make sure you use Schottky) will limit the voltage at the input to the range of about -0.3 to 5.3. If the total load on the regulator is more than 10 mA, it will be able to compensate for the current excursions.

There will (possibly) be a slight bandwidth reduction caused by the R1/ADC input capacitance acting as a low-pass filter, and the ATMEL data sheet does not seem to provide any information about input characteristics along this line. However, with a maximum conversion rate of 15 kHz, this seems unlikely to be a problem.