DIY-WB Output Voltage Scaling

[Peter Gargano]

It should be pointed out that the current incantation of the
DIY-WB unit has a non-linear voltage:AFR transfer function.
The actual transfer function is described here:

  http://www.diy-efi.org/diy_efi/projects/diy_wb/

See "Output voltage/AFR reference". A graphed version is here:

  ftp://ftp.diy-efi.org/incoming/DIY_WBafrVolts.gif

The curve can be thought of as a series of straight lines
for simple interpolation, but it means that a simple digital
panel meter connected to the WB output with a simple scaling
circuit will not be able to show accurately a large range of
AFR ratios. This is why I suggested the Jaycar kit/Silicon Chip
kit with 16F84 PIC and 3 digit display that comes with source
code that could be modified to scale the DIY-WB's output to the
above transfer function.

If you're logging the DIY-WB's output and post-processing the
logged voltage, then this isn't too much of a problem.

For the DIY list, here's the information I posted to GMECM
yesterday.

Product Name:        DIGITAL FUEL MIXTURE DISPLAY KIT
Catalogue Number:    KC5300
Price:               AU$62.95  (less than US$35) + freight

  http://www.jaycar.com.au/home.htm

Peter.

Disclaimer: I have no affiliation with Jaycar, and their
web site is a bastard to use.

(Jaycar - fix it!)
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