I'm working up a sensor that measures the resonant frequency of a bit of wire using a piezo element (see attached photos). The wire is "plucked" by the electromagnet below it and freely resonates. The idea is that as mass accumulates on the wire (freezing water) the resonant frequency will be reduced. This type of sensing methodology has been used in the past, but I'm afraid I'm overcomplicating the signal conditioning here. All I'm interested in is the frequency response to the plucking, so greatly amplifying the signal to the point of a square wave, then counting crossings seems more sensible that full FFT, etc.
That being said, I've considered and played with instrumentation amps, JFETs, and JFET based op-amps like the TL071 and a circuit like this
. Any thoughts on the best/cheapest approach here (disposable sensors)? I know I'm overthinking/complicating the situation as it's not really precision instrumentation and I'm fighting the urge to properly DC offset, etc. For what it's worth - I hooked it up to an INA128 setup on a dual supply and got nice results with gains of 1-5k. This circuit will be signal supply in it's final state though.
Any thoughts appreciated!