Air/Fuel Monitor

[bcroe at juno.com]

Nothing wrong with a meter with a needle for a readout.  
The main problem is finding a large one that is economical 
and available in quantity.  Maybe a DC to pulse circuit 
would allow use of a standard Tach meter, with a new
scale of course.

It is possible to double the brightness of the DIY bar 
graph with a corresponding increase in power.  Even 
this is probably not enough in direct sunlight; a shade
might be needed.   

Trying to get a specific reading from a narrow band 
OX sensor is difficult; they are usually used in the 
switching (never stable) mode.  With a Wide Band
a typical response is some flashing between 3 LEDs
out of 20 covering 14.7:1 to 10:1 A/F.

It certainly is possible to slow down the response 
speed of a bar graph to that of a mechanical meter 
or even more (a mechanical can be slowed more 
too).  I'm working on a simple filter to do this now.  
With the high input impedance of the LED display, 
it just requires the right capacitors/resistors.  I'll 
suggest some specifics after testing, snow may
get in the way.

Bruce Roe

On Wed, 26 Dec 2001 09:49:38 -0600 Erik Quackenbush 
<erik at midwestfilter.com> writes:
> When I put an A/F meter in my TR6 I started with a bar graph LED 
> display 
> like you but I later switched to an analog gauge from Westach 
> (http://www.westach.com) which I find MUCH easier to read in bright 
> sunlight. The other problem I had with the LED display is that it 
> changed 
> so quickly that I spent too much time looking at it and not enough 
> looking 
> at the road. The needle on my analog gauge moves slowly and give me 
> a much 
> better idea of my average A/F ratio at idle and cruise. I suppose 
> you could 
> put a low pass filter on the input to the LED display for the same 
> effect 
> but the needle gauge looks right at home under my dash.
> 
> For a much more accurate A/F meter you might want to look into the 
> DIY-wideband O2 sensor project from the DIY-EFI 
> (http://www.diy-efi.org/diy_efi/projects/diy_wb/) mailing list. 
> Standard O2 
> sensors are only accurate for a small range around stoichiometric 



> -Erik

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