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'''VR trigger fan noise''' This page is about a strong (600W) PWM fan in a car, located in close proximity of the crank VR trigger: http://quasar.dynaweb.hu/~lezsi/vems/bmwtrigger/fannoise/vr_sensor_fan.jpg I've found the strange situation of VEMS starting fuel pumps and injectors with stopped and stand-still engine when the fan operates. Apparently the fans magnetic field is strong enough to trigger the crank VR signal- Scope shot of this noise measured on VR signal cable: http://quasar.dynaweb.hu/~lezsi/vems/bmwtrigger/fannoise/fan_noise.gif It's in the range of +-0.5V, more than enough for LM1815 triggering This is a normal scope trace of cranking the engine -without fan operating: http://quasar.dynaweb.hu/~lezsi/vems/bmwtrigger/fannoise/clean_trigger.gif I'm looking for solution of this problem. Since the signal/noise ratio is around 10/1, I've the idea to attenuate the VR signal with a series voltage divider at around 1:10 ratio. ---- [dnb] I too have seen this problem, but when headlamps are turned on or off with the engine not running. When the engine is running the LM1815 chip seems to be doing a good job suppressing noise so I am not too worried about the problem but a fix would be nice. I am not convinced your attenuation idea will be completely successful - it might make the car hard to start when the VR signal is small at cranking speeds - but please keep us informed. I have in the past used a 6dB "pi" attenuator so I can monitor crank triggers using a USB sound card (when trigger logging with VT was not available). It can be simply made with 3 resistors. I used the following to get impedances matching my requirements. R1 = 13k1 R2 = 16k8 R3 = 3k6 Since the trigger is made of relatively low frequency sine waves, maybe an additional band pass filter could be built in to the front end? I suspect though that it all comes in at the same set of frequencies... It's difficult to tell without being able to look at an FFT of the data. ----
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