# Measuring negative voltage given by a coil using Electromagnetic induction

johnerrington:
I like dlloyd’s solution, post number 9. Simple & effective

every arduino “experiment kit” is different, but all you need is a couple of same value resistors (say 2* 1k - 2*10k) to provide a mid-point voltage; and I’d add a capacitor from mid-point to ground just to decouple;
and a 100k to protect the arduino ADC input.

That 100k is too large, 10k is better, as the ADC is not characterized to perform as per the datasheet
unless the source impedance is 10k or less. Frankly the two resistors giving the mid-rail voltage are
also providing protection so its moot if you need the third resistor, but resistors are cheap.

That 100k is too large, 10k is better

100K will give voltage protection up to 100V ... the OP could measure 30V max, but there's the risk of higher voltages. Maybe 10K with an external Shockley diode to Vcc.

the ADC is not characterized to perform as per the datasheet

.. in terms of conversion time.

dlloyd:
100K will give voltage protection up to 100V … the OP could measure 30V max, but there’s the risk of higher voltages. Maybe 10K with an external Shockley diode to Vcc.

Hey, my name is Schottky!

Forgive my spelling sir!
I do appreciate your invention ... I need lots of them!

@emielj ... any progress on your project?

Paul_KD7HB:
The difference between S waves and P waves is 90 degrees. As in the quote you gave, S waves are vertical and P waves are horizontal movements. S waves bounce your house up in the air and then the P wave moves the foundation out from under it.

Paul

I lived in California for 25 years and that is the best layman's explanation of the different Earthquake energies.

dlloyd:
100K will give voltage protection up to 100V ... the OP could measure 30V max, but there's the risk of higher voltages. Maybe 10K with an external Shockley diode to Vcc.

An op-amp as I described above would limit the output swing to the rails.