This screen shot from the 30 page Pat #4163437
shows exactly how they work. I'll say one thing for
them they sell for less than $10 in some cases.
You won't beat the price. The question is: will they
work at 7000 RPM because lawn mowers rarely run over
3600 RPM. The voltage and current go up with
RPM so the semiconductor and resistors may fail at 7000 RPM.
I think I'll get one and experiment with it.

Paul Lamar

Paul,
Didn't I read on one of those web sites of the newsletter  that the device
can be stepped for higher RPM.
George ( down under)

You got me.

Paul Lamar