We are building a system that interfaces an approx 3-20 KHz square wave that comes from an engines crank position sensor. It is an open collector sensor, so we have a 1 KOhm pullup in our system to track it. We currently use a simple 74 series buffer to turn this into a "safe" signal for our 3V3 MCU, however, some slight electrical noise/ringing etc causes our MCU to miss trigger. The stock ECU of the car (and others) can "live" with this noise without issue, so must be using a decent filtering system. We will be scoping the system today to get a better picture of what the noise is.
Is there a simple hardware method to clean this up? I am thinking a schmitt trigger but open to ideas?
This is the signal presented to my conditioner, which is a MAX9926 IC into the +ve line only, -ve left floating
Here you can see for some reason always at a certain RPM, the VR conditioner "drops it" 9Yellow is signal into MCU after MAX9926:
Here is the Max9926 system. This signal is Fed into CAMVR+. CAMVR- is left open circuit (floating). Also, a 1K pullup is attached to CAMVR+ to 5v to give us our voltage due to the open collector nature of the sensor.