Single cylinder bike engine
We get trigger noise from the ignition system. Initially we did not use shielded cable, as it is not shielded on the stock engine. But the noise goes away with just using a shielded cable, not even twisted pair.
- The primary trigger has 12-1 teeth and a 230 Ohm VR sensor, see more info below with scope shots from low rpm, typical cranking.
- The trigger input is the stock VR standard that you get when you order an ECU with VR input. If I understand correctly it has an 18 kOhm pull-down to ground.
- The coil is a stock KTM, measures 2.3 Ohm on the primary and uses NGK plug hats. We use NGK BKR8E-11, and has a resistor.
- The cross kart chassis is quite small, has a small motorcycle battery that the engine and chassis are grounded to in a proper fashion.
What would be a good filter for this type of noise?
Preferrably something that can be implemented inside the ECU.
Would it be correct to say that the ignition noise is constant but that we would get a stronger signal with increasing RPM? That is the usual way these sensors work, I would just like to buy some more immunity to noise.
Saved for historic reasons
I'm helping a guy that is building a cross kart engine, it's a Honda 650 cc 4-stroke (about 80 hp). It has no suitable trigger wheel for exact timing and cam sync. We are adding a 12-1 trigger with VR sensor which is custom-made and adapted from a KTM bike engine with the same sensor and we copied the wheel design (teeth length, depth, width) other than the KTM one uses 18-1. The gaps are about five times longer than the teeth.
This type of trigger is not of zero crossing type, more of level crossing type, which might mean we need special adaption on the trigger input. The sensor is 230 Ohms and below follows scope shots of the trigger. The missing tooth does not overshoot much, what do you think? - the VR signal looks very good, should be no problem
[12-1_40rpm_60us.PNG 
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[12-1_150rpm_0.5ms.PNG 
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[12-1_300rpm_0.4ms.PNG 
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[12-1_300rpm_30us.PNG 
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