Hi,
I'm using a piezo electric (same example than knock learning on arduico.cc). I'll detect BIG knocks and I need to protect the anaog entry.
I can use a zener like this : Spooky Arduino Projects #4 – Musical Arduino – todbot blog
But on the knock example, they use just a 1m resistor? would it be enough if the piezo generates 20V ?
What about sing a 10M ? could it replace the zener solution being more simple?
Thanks
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the zener with a 1 meg resistor should be fine. A Piezo sensor produces very low current and the zener will absorb the higher voltages without problem.
Using a higher value resistor won't work and a lower value will reduce the voltage but does not limit the voltage in the way a zener does.
Good advice as usual from mem.
My personal preference would be to use catcher diodes to the supply rails as in :-
http://www.thebox.myzen.co.uk/Tutorial/Protection.html
Given N engineers there will always be at least N+1 firmly held opinions. 