I would like to validate this design I use for input to a microcontroller for a piezo microphone trigger. I use 3 lines: a Schmitt trigger for use with an interrupt, an analog line for measuring the voltage level in the ADC, a reset line connected to a transistor to discharge the ADC capacitor.
The first path going from L1 (ferrite bead) to Q1 rectifies and RC filters the the AC signal comming from the mic piezo. The result is then split to both op amps U1 and U3.
I have a couple of questions regarding this design:
- Do I need R2 and R3 to stabilize the input of U3 and U1?
- Does it makes sense to control Q1 with a microcontroller to discharge the C1 capacitor after the reading was done the the ADCInput line in the micro?
- Is it overkill to put a ESD protection TVS diode at the very start of the signal chain?
Here are the signals I expect from LTSpice:
Red = Piezo signal (-5v/+5v)
Green = D2, C1, R1 filtering result before going to the opamps.
Blue = Schmitt trigger ouput
Any other comments/suggestions/links would be greatly appreaciated.