eliotroyano
New Member
Hi friends. This is first post after reading these useful forums during some days. I am from SouthAmerica and have some time working with electronics. I post this my first topic looking for some ideas.
I have been looking for simple circuit solution about removing an offset from automotive square signal (tachometer or rpm signal from car ECU - engine control unit) that you can see it attached here. The signal is a more or less stable 50% duty cycle frequency variable (25-256Hz) signal with a 9VDC offset that lives from 9 to almost 14VDC. To be usable for my datalogging purposes I only need the frequency variable square part of the signal, without the offset. I mean from ground or 0 level, or at least that reach less than 1VDC for a low level and more than 3VDC for a high level.
I have tested a simple high pass filter with a series capacitor (0.1uF) and a clampling diode, but the signal goes almost to the ground level as small non usable erratic pulses around 0.5VDC. I also try to reconstruct that signal using a comparator (LM311) and 12VDC reference with a resistor and 12V zener diode. But on bench it works quite good but in the car it only show a Hi level signal as an output.
Well friend, I appreciate some tips and ideas to solve this little issue that is going big.
I have been looking for simple circuit solution about removing an offset from automotive square signal (tachometer or rpm signal from car ECU - engine control unit) that you can see it attached here. The signal is a more or less stable 50% duty cycle frequency variable (25-256Hz) signal with a 9VDC offset that lives from 9 to almost 14VDC. To be usable for my datalogging purposes I only need the frequency variable square part of the signal, without the offset. I mean from ground or 0 level, or at least that reach less than 1VDC for a low level and more than 3VDC for a high level.
I have tested a simple high pass filter with a series capacitor (0.1uF) and a clampling diode, but the signal goes almost to the ground level as small non usable erratic pulses around 0.5VDC. I also try to reconstruct that signal using a comparator (LM311) and 12VDC reference with a resistor and 12V zener diode. But on bench it works quite good but in the car it only show a Hi level signal as an output.
Well friend, I appreciate some tips and ideas to solve this little issue that is going big.