O2 sensor meter

[Orin Eman]

> At 09:08 AM 6/14/97 +0200, you wrote:
> >I have made the EGO sensor meter for my car, but I have found that the
> >voltage across LAMBDA sensor is not stable.
> >I mean, when the engine is running at its minimum (about 800 RPM),
> >the voltage go up and down around 0.5 V with a frequency about 3-5 Hz.
> >Why?
> >How can I connect your EGO sensor meter in order to have a stable value?
> >

> O2 sensor voltage is supposed to oscillate at idle. There is no way to
> change this behavior.  If you mixture is set wrong (too rich, too lean)
> then the voltage will stick to one end of the range.

If this is an LM3914 based meter, you can add some low-pass filtering
at the input to smooth the oscillations.

I have EGO -> 1Mohm -> 0.1uF to ground.  The LM3914 input is taken from
the 1Mohm/0.1uF connection.  This smooths things a little (.1s Time constant).
I'd try .47 to 1uF to really average it out.  You do trade off response
time though... the meter would be slower to respond and would miss
transients.

This doesn't seem to load the sensor any worse than going directly to
the LM3914.  DC input impedance is that of the 3914 plus 1Mohm... it
drops to 1Mohm over a few 10s Hz (deliberately vague here).

Orin.