I am trying to build digital tachometer for my motorcycle Yamaha FZS600 Fazer 2002. I have a problem with reading signal from CPS sensor. It is hall effect sensor, I suppose. I found the plug of it. It has two wires. One is GND so the other must be the signal. I have no oscilloscope to probe it so I connected it to the soundcard oscilloscope through the voltage divider and op-amp as can be seen in below schematic.
– Schematic created using CircuitLab
I adjusted the R1 and R2 values with a 10k potentiometer and got signal presented in picture 1. It looks nice (it looks like it would be no problem reading it with a uC).
In the next step I connected the same circuit to a analog pin of an Arduino and uploaded simple program to constantly read voltage on that pin and transmit it through serial. The result can be seen in picture 2. That doesn't look like the waveform from picture 2 at all. First of all the signal read by a soundcard is inverted but it is reasonable. The signal read by an Arduino is meaningless. The question is what is the proper circuit to read a signal from such sensor.
The LM358 is single-supplied from 12 V with a 1uF capacitor to GND. Adjusted values are: R1 = 9.27 kOhm R2 = 1.79 kOhm
With no voltage divider or with smaller R1 it seems that my circuit disturbs motorcycle's ECU reading of CPS and the engine runs unevenly or stops.