Sudo wrote:But amplitude and the shape of the waveform are meaningless here. ONLY zero crossing matters.
I wanted to poke this comment a bit. The amplitude can give some information about RPM. However it's often not used. For example with chips that I have never seen, you could use the amplitude to change the band pass center frequency as a kind of kalman filter. Such a filter could be handy mostly for removing noise from the system when at low RPM. If you see a large amplitude spike when you expect a low amplitude spikes, you could ignore the spike as it has to be noise.
So how can this be applied to a simulator board? The simulator board should allow playback of the log file information. I agree that the MAX232 chip + and - ouput is better then several other options, and I also agree it can be better. For example, there are op-amps with differential outputs, that could be driven to make an exact match to the real signal. The goal with the MAX chip is that you play back a log file, and get the same TTL signals. Those TTL signals are handy for validating pieces of the system and allowing desktop development. The MAX232 chip is also low cost and easily bread boarded.
The problem that russian is seeing is most likely due to a wondering DC offset similar to the picture posted above with the "real 0 crossing" comment added. See modified picture below, notice the length of the noise in the middle is the source of the errors being detected. When that noise is short enough, it doesn't trigger the energy detected. However when the noise is there long enough, it triggers the energy dector and creates false triggers. It doesn't take much to bugger the VR signal.
- 7_27_10_raw_vr_vs_lm1815_output_NOISE_modified.jpg (116.95 KiB) Viewed 24663 times