Proper Mixture.

[Frank F Parker]

> A simple and effective indicator for O2 sensor is a DPM (digital
> panel meter) from Hosfelt Electronics.  It is $14.95, their part
> number 39-165 (the part no. on the data says PM-128).  It uses an
> Intersil ICL7106 DMM chip with a fairly standard wiring.  There is
> one problem -- they have connected the supply voltage common with
> the input common, which can cause ground loop problems  -- I solve
> this by using a 9 volt battery (actually I was lazy and that was
> just the fastest way for me to get it up and running).  The 9
> volt battery lasts about 6 months.  One could use a simple resistor
> and zener or LM-317 to run it off the 12 - 14 volt battery system
> (I don't think it wise to run it straight off the auto's battery
> system).

This is a good meter but I am pretty sure the power supply ground and
the measuring circuit ground can not be the same. Thus can not run on
car voltage and still measure o2 volt which has the car gnd as common.
I have also used a 9 volt battery.  That's why they are cheap.

	frank
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