Hello,
I have a solenoid driven by a car injector driver (see picture). I would like to analyse that wave (duration measuring) with an Arduino. As in the picture the back EMF can go to 100V. The arduino supports only +5V. How can I clamp that the safest way and attenuate it in order to have a block wave without the spike at the end. Thanks

 

One resistor in series with the input and a signal quality (small) diode connected to the +5V rail will stop the voltage from going higher than 5.6 volts. Then you can do a 2 resistor voltage divider to cut it down to 5.0 volts.

 

One resistor in series with the input and a signal quality (small) diode connected to the +5V rail will stop the voltage from going higher than 5.6 volts. Then you can do a 2 resistor voltage divider to cut it down to 5.0 volts.

Thanks fr yr answer! I guess 10K is OK . Do I but the diode after it or is'n that importan

One resistor in series with the input and a signal quality (small) diode connected to the +5V rail will stop the voltage from going higher than 5.6 volts. Then you can do a 2 resistor voltage divider to cut it down to 5.0 volts.

Thanks. Do you think this diagram (picture) should do it?

 

Move D1 to the left of R4.
Move R1 to the right of R4.
Change R4 to 6k.

 

Move D1 to the left of R4.
Move R1 to the right of R4.
Change R4 to 6k.

Your diagram is indeed more within spec for arduino input. Thanks!