Ok thanks, so I will do the diagram @jim-p sent, adding a 1Megohm load across the piezo; but maybe with 1N4148 diode rather than the 1N5819 Schottky diode mentioned ?
As for the magnetometers, can I do the same (but excluding the top part as I only ned negative clipping)?
No, must use 1N5819
That circuit will clip the negative voltages.
If you need the negative voltages then a different circuit is needed
As for the magnetometers, can I do the same
No
Use this circuit::
Piezo :
Alright thanks, but would the internal leakage mentioned by @Wawa be a problem as I need to measure ecg from low current with low mV variation?
Magneto :
I already have a voltage divider converting 0-25V to 0-5V (DF robot link) and as mentioned, i want to clip the negative voltage to maximise the 8bit precision of the R4 DAC on the positive range : is there a way to do that with my DF robot voltage divider + a diode ?
Does that piezo device output negative voltages?
According to the datasheet the output range is 0 to 1V.
A piezo can only output AC, not DC.
Not sure if the negative half needs to be measured.
It seems that the sensor is a contact microphone.
Leo..
well usually only around 20mV-500mV indeed, but as I said in my intro post :
and thus I want to protect the arduino from that
Thanks, in this casse there would also be a cable from the (-) pin of the sig going directly to Gnd right?
Probably but I know nothing about you magnetometer so I can't say yes for sure.
Thx but I feel like this would be a bit overkill for a piezo no, like the circuit you showed before (see quote) seems enough ?
Well if you add two more resistors to that circuit you can have gain. Amplify your 500mV signal to around 3V.
If you use the 2 diode circuit then as @Wawa pointed out you will need to use 1N4148 diodes and a 1K resistor
As already pointed out, the piezo sensor could generate positive pulses as well as negative pulses. you can only detect negative pulses by floating the sensor pin mid-voltage.
Leo..
