So what is a low cost vibration detection package that might interface to a suitable ZigBee module as an optional sensor to that below?
Planning to feed a Zigbee module with a variable resistance (0-500K linear) to the A/D converter for a strain measurement
in all the standard applications.
A SAG Mill turns at about 15 RPM. The frequency range of the breaking rock is definitely in the audio range where the rock drops back from the lifted position to hit the charge in the bottom of the mill. The charge of ore and steel crushing balls is typically about 25% of the total volume. There could be frequencies detectable above and below the audio range but need to confirm.
A SAG Mill turns at around 15 RPM to break rock. 
