As promised here are the details of the RPM signal filter I designed and built based from various sources of other filters online.
I found many of the filters didnt work for my bike for various reasons. So getting my thinking cap on I started making a couple of little tweaks.
So here it is for public consumption.
Now WARNING! , dont assume this will just work on your bike. This isnt perfect. while this does work on my bike with its coil noise characteristics it probably wont work on yours without some modifications. Test it on a breadboard first, and be prepared to make some changes.
The duty cycle is very very short. and the signal reaching the Opto Schmitt is a little on the weak side. But enough to trigger every time, at least on my bike. i tried to fix this by placing the cap before the first resistor for it to get more charge. This in part worked but it also smoothed off and kept the fly back ripples strong enough to also trigger the Opto Schmitt. This caused an echo pulse, doubling the RPM read.
Placing the Cap after the resistor allows the resistor to dampen down the fly back ripples. But keeps the signal on the weak side. Maybe youll have more luck or a better idea. Prehapse lowering the resistor level a little.
The signal out of the Schmitt is inverted. So your MCU needs to be programmed to accept that signal or you can invert the signal back.
Maybe its the opto schmitt i used? I thought this trigger wasnt meant to invert. I guess the inverter is actually caused by the +5 being attached to the signal out line. So whats really happening is when the Schmitt triggers its dumping to ground internally giving me the inverted signal.
Anyway this is the design as used in my speedo project... Feel free to use this or make improvments.
If you do make any improovments please let me know... I might need them too :)