DIY WB update

[Barry Tisdale]

DIY-EGOR builders:

Got the DIY WB O2 sensor project completed and adapted to my ECM (7749 -
Syclone) and data reading software.  Thought there might be some interest
among other WB builders as to how this worked for me.

The voltage output given in the schematic sheets varies from -2.2v @ 10.6
AFR to around +.52v @ 17 AFR; this is referenced to "fake" ground.
Variation in relation to true ground gives 2.0v to 5.1v.

One more LM324 is fed this voltage, divided down, referenced to true ground
and an offset is applied to the negative input pin - this gives a range of
75mv to 1125mv, more in the range that the ECM wants.  The voltage / AFR
ratio is reversed from what the ECM sees in a standard oxy sensor, however.
 I originally planned to replace the standard O2 sensor w/ the WB - my
chips are all open loop, so no actual engine controlling done using the O2
sensor.  

My preference was to keep the stock O2 sensor and *add* the WB output to
the ALDL data stream - how to do this on a cheapo laptop was the problem.
After considering and trying several approaches, what finally worked well
was to give COM1 on the laptop a choice of two inputs - either the ALDL
adapter, which runs @ 8192 baud *OR* a serial I/O board from Weeder
Technologies which runs at a standard 9600 baud.  The switching is done by
using two data bits from the parallel port to toggle a CD4066 CMOS switch
to choose between either of two serial inputs to the serial port on the
laptop.  A small board plugged into the printer port of the laptop has
sockets for the two serial inputs and one output to the laptop serial port.
 The data logging software (written in QuickBasic, DOS only) then toggles
between the two serial inputs, switches the baud rate by means of IN and
OUT instructions to the control register of the serial port.  After the
normal ALDL data stream is read, the Weeder board is then read to get the
WB oxy value; this value then replaces the unused (no EGR active, either)
"EGR desired" data byte in the 7749 data stream.  The data display software
(EFIlive by Paul Blackmore) then does the math on the data and graphs
accordingly.  Right now I'm using a conversion formula, even though the WB
output isn't linear with respect to voltage vs. AFR.  Close enough for
government work, though, as I'm really looking for relative values at this
point.  If 'calibration' of these units is ever possible, then I can go to
a lookup table instead.

So far, this is a benchtop unit - have a bit of work to do to turn the
spaghetti tangle of jumpers into a vehicle mounted unit, but she *works*!

Additional benefit is that the Weeder board has eight ADC inputs available
- room enough to monitor WB oxy, EGT, fuel pressure, etc - more than I'd
hoped for.

Special thanks to Chad and Bruce for making this whole thing possible -
what a *neat* gadget - helped to pass a dreary winter!

Barry - Syclone #26
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