I attache a JPG picture of what I did in reading the pulse voltage from ignition coil. I try to make a tachometer from this concept, pickup signal of ignition process then integrate the signal, count and display. But the point is that I don't know how high voltage is when I pickup from the ignition line.
I did measure with the multimeter at the same point as show in the JPG, but the voltage displayed vary if I change the max. limit on the multimeter. I did not move the point on the measured line. In fact, at first I set the max. limit to 600V and it read 36V, then I think I can use max. limit of 200V but it read 3.6V. Max. limit of 20V, it read 0.36V.
Are any experts have explanation for me, please?