O2 sensor pullup resistor values?

[Phil Hunter]

A while ago I built a similar circuit for a twin
turbo drag car running a '7148 ECM. I used a very
high impedance JFET op-amp to get 0.454V open circuit
and then w/ a 19.7Mohm resistor across the circuit I
got 0.427V, solving for Rx gave 1.2Mohm. Hooking up
the unheated O2 sensor gave no voltage change, but w/
a heated unit the voltage quickly headed to 0 in less
than 30 seconds as I recall, used sensor, YMMV...

For the ECM input, my logic was the ECM should see
the leanest mixture, so I used 2 "precision rectifier"
op-amp circuits out of Walter Jung's IC Op-Amp
Cookbook into the summing point. For the 0.45V bias
supply I used an LM10 which has a built-in 200mV
reference, and a 7660 was used for the negative power
supply.

Since the car isn't finished, and they're switching to
an Accel DFI, and the WB circuit has made my circuit
obsolete, I have no real world testing results to
report, but the ideas may be useful.

regards,
phil
(digest)

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