DIY-WB Output Voltage Scaling

[Bob Wooten]

Peter,

I guess that I was not paying enough attn, I did not see the curve (it did
not occur to me to check it out).  the more that this gets developed, the
more I think that this is a very good application for a Basic Stamp or Basic
X.  we have just started using them @ work & I have one here that I have
used to turn on & off LED's.  Mind you I am not a genius when it comes to
this stuff, but it seems that this would be a great application for this.  I
can get small RAM's for next to nothing & DACs for a small fee.  the thing
that cost the real money is the controller itself. the advantage here is
that I can add in a table for linearizing it & have it do the math for me
right down to the accuracy of the look up table itself.  We just got a
couple of serial displays for test equipment, that were pretty cheap.

I think that once I have my DIY WB up & running I am going to try to emulate
it with the stamp & see if I cant get the heater algorithms close to what
the DIY WB is doing.  I think that once I get that fingered out the rest is
cake.

Just thinking out loud.

BW

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
Behalf Of Peter Gargano
Sent: Friday, August 24, 2001 4:36 PM
To: gmecm at diy-efi.org; webmaster at jaycar.com.au; diy_efi at diy-efi.org
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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