RuggedCircuits:
You have a few problems:You are using "pin 2" for reading but your schematic shows your input hooked up to analog pin 2. That is not the same as "D2", or digital pin 2. Move your input from A2 to D2.
Second, nowhere in your code do you write to the oldTime variable. You must say something like:
oldTime = newTime;
newTime = micros();
thank you very much!
for some reason I thought that the interrupt uses analog pins 2 and 3.
and the oldTime assignment to the newTime had in writen algorithm on paper, but forgot to copy it :doh:
now the rpm meter works!