DIY-WB Output Voltage Scaling

[Glenn & Debbie Woodhouse]

A couple of questions for Peter and the group.  Peter, the display kit you
recommend sounds perfect for our application.  I looked at the Jaycar info
and it does not reference the supply of source code.  Did you buy one or
talk to Jaycar to confirm this?

Secondly, to the DIY-WB group, I have the transfer function for the NTK
TC-6110 series UEGO controller box.  This transfer function reflects the
$600 NTK sensor which many of us feel is effectively the same sensor as the
Honda (DIY-WB) part.  The NTK transfer function voltages run exactly 0.5
volts greater than the DIY-WB from A/F 10 through stoich, and are close
enough for tuning purposes in the lean range taking the 0.5 V offset into
account up to A/F 20.66 (within 0.3 A/F).  My question to the DIY-WB
designers is, is their a voltage offset or bias in the design that would
produce the 0.5 volt shift?  Has anyone played with the NTK box and
determined if it produces a 0.5 V bias? Or, perhaps the high dollar NTK
sensor (and/or controller box) actually produce ion pump output currents and
resulting voltage conversions that are different than the Honda sensor
(and/or DIY-WB controller).

Thanks, Glenn.


------------------------------

Date: Sat, 25 Aug 2001 09:36:14 +1000
From: Peter Gargano <peter at techedge.com.au>
Subject: DIY-WB Output Voltage Scaling

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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