Re: O2 Sensor monitors

[rdh@sli.com (Robert D. Houk)]

   You are right Scott ... there really isn't that much to making an O2 sensor
   monitor display.  I haven't checked lately, but National Semiconductor used 
   to make an IC that would drive a bar-graph display based on an analog input 
   level.  Add an appropriate high-impedance input amplifier and something to 
   give you the desired scale-factor and you're done.  There is some value to 
   the reduction of this to practice however.  I don't know that I care that 
   much about having an O2 readout on my dash though.  If only SunPro would 
   have built that function into their hand-held auto meter.  

Yeah, sigh...

While I'm sure the basic circuitry is about $5's worth of components, re-
member we're talking Audi here, so you are morally obligated to pay at
least 4-5 times what it is rationally worth . . . plus you are paying for
nice packaging (not to mention "research" and development) . . . and
keeping all those poor starving clerks off of welfare . . . 

I'll try to remember to look this stuff up tonight (I scored a copy of some
Bosch info), but the basic "curve" is a very very steep step function, from
a touch over 0.0V to a touch under 1.0V (the O2 sensor acts like a voltage
source), with 0.5V being stoichiometric ideal. A "linear" 0-to-1 voltmeter
will almost certainly give you n/2 "totally lean" readings, and n/2 "to-
tally rich" readings . . . certainly if your resolution is 10 steps (as in
the vanilla LED bargraph). Assuming I can remember that far into the future,
I'll look it up and post it tonight.

					-RDH