I need help on a circuit I've designed to detect hits on a piezo sensor on a drum. It uses an opamp with 2 channel, on goes to a schmitt trigger, the other to the ADC input on the XMEGA microcontroller. Once the interrupt for the schmitt trigger is raised, the reading is done on the ADC and then a reset pin activate a transitor that flushes the excess signal.
All of it works super fine as expected but there one little catch: I'd like to increase the sensivity of the schmitt trigger by a fixed value. The opamp I'm using to feed the schmitt trigger gets maxed out when I apply the maximum gain on it. On the side of the ADC channel, all is good, the signal is within good range (about 0V-4V).
Now here is the question: is there a way I can use this exact(ish) circuit and maybe add a resistor or 2 somewhere or remove one to bias the input of the schmitt trigger of let's say +1-2V? Since the threshold of this particular schmitt trigger seems to be about 2.2v when Vcc is at 5v but I want to detect signal to about 1-1.5v as well.
My background is software/firmware development so I'm a bit lost on what to do to solve this problem without having to redo the whole things (which works fine but isn't sensitive quite enough to my taste)
Schmitt trigger used is: SN74LVC1G17 Opamp used is: ADA4075
Here is what the board looks like (it if may be of any help), so there is room to solder jumpers or resistors around without having to older a new set of board: