Here's the second edition of the document that describes how a simple ion sensing ignition timing feedback system can be built. Ion sensing is a technology that can be used by an engine control unit (ECU) to correct the car's ignition timing automatically, on a cycle-to-cycle basis.
Some older documents
- An enhanced version of the sensor circuit used in the system below (76kB PDF) (old)
- PDF version only, available here (170kB) (old)