Voltage limiting circuit for oscilloscope

[holabr]

I am looking at using an oscilloscope app on an iPhone. It uses the microphone input to connect to a probe. Since the max input is 1 volt AC, what kind of circuit do I need to build to front end the probe to protect the iPhone from an over voltage situation or is this the function of the probe? Is there a simple way to build your own probe? It doesn't have to be highly accurate because I am just looking to play around with it to learn a little about using a scope. It also doesn't require me to bring another piece of equipment into my house. My wife already thinks I have too many "toys".

 

[MikeMl]

Do you know what the input impedance (input resistance) of the iPhone is?

A series resistor about 1/10 of the input resistance, using four 1N4148 diodes as shunt clamps as shown below would go a long way to protect the input from excessive voltages.