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Originally Posted by alantf
I remember in the old days, working on cars with the old fashioned mechanical breakers, that had to be changed every few thousand miles. They worked fine (until the contacts started pitting), so I would have thought that in this day and age, someone would have come up with a cheap solid state version that would do the same thing, but in a better way. :??:
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They have
They've replaced the mechanical complexity of the gears driving a distributor with a Hall effect or VR sensor on the fly wheel that tells the magical electronic ignition box when the piston is at TDC. Following the KISS principle we don't care whether it's on the combustion stroke or exhaust so we'll just fire the plug on both. If we did care we'd have to violate the KISS principle and add a cam position sensor to determine when the piston is at TDC on the power stroke. This does have some advantage when it comes to multi-cylinder engines and fuel injection.
The magical electronic ignition box takes care of ignition advance based on rpm. On more advanced systems there might be a throttle position sensor that combined with RPM can calculate engine load and adjust ignition advance accordingly. You could get more fancy (accurate) measuring engine load by adding a manifold air pressure sensor to the sensor mix. This magic in the ignition box replaces the vacuum advance or centrifugal advance from distributors of yesteryear
So essentially a cheap crank position sensor and electronic box replace the old school distributor.