And again, you do realize that a regular 2 wire O2 sensor doesn't tell you what your A/F ratio is, it just tells you if you're running rich or lean. And it only tells you that if let it switch between rich and lean.
The ECM's don't try to maintain an exact .5v from the O2 sensor (that's practically impossible), they run the engine just a bit leaner, wait for the O2 sensor voltage to drop, then run it a bit richer, wait for the O2 sensor to rise, the start the process over again. They call it 'O2 sensor crosscounts'. On normal engines (well, ok, mine for example, '01 Dodge Ram), I measure around 30 cross counts, which means 30 times second, my truck's computer has recognized that the O2 sensor has swung lean, so it richens up the mixture, then it see the O2 sensor swing rich, so it lean out the mixture.

See that?

Do a Google search for 'MegaSquirt' do-it-yourself fuel injection system, you'll see what I mean by all this.

JDG