SPI not working - Teensy 3.2

[alonper]

@bmillier
Thanks again.
Yesterday I decided to connect the Piezo sensors straight to the SGTL's LINEIN.and suprisingly It actually works OK but with some constant noise around 3.8KHz.
so for now, no buffer, no filter..
It is not strange if we take in account that the piezo has really big impedance?

I think that I should try to connect the piezo straight to the buffer you suggested to get some gain, for that I should feed the negative supply of the op-amp? (with the ICL7660?)

 

[bmillier]

Well, depending upon use, a piezo can put out a pretty big signal, so even if you load it down with the 29k input impedance of the SGTL5000, its not surprising you could still have enough signal to work on the max gain settings of the SGTL5000s line input. In fact, if there is any chance the piezo could get a sharp hit, it would be a good idea to have the buffer in place to protect the sgtl5000 from a large transient pulse.
No - you can continue to power the buffer from the single 5v supply as you do now.