2.8V on the signal line according to Link manual. What voltage would represent significant knock?

 

Without trying to be funny John the best way is to apply some shock, carefully, adjacent to the sensor of differing levels and look at the output with a scope, I have never found a defined voltage for "knock", the sensor is basically a piezo microphone.
Don't tap the sensor directly.

 

I tap the bolt holding the (knocklink) sensor lightly with a key once in a while to test it - it always lights up to the red!

Richard

 

Thanks will try that (gently!)