Modifing O2 output

[Black Feather Electronics]

On Wed, 27 Sep 1995, Robert Gallant wrote:

> I need to modify the output of my O2 sensor (specifically I need to drop the 
> voltage my computer sees from the sensor).

I called around to many places to find out what the output is on most O2 
sensors and it seems they are mostly 0 to 1 volt output.

The way to test this is to take your sensor, put it into a vice and fire 
up your propane torch.

The sensor must get hot before it puts out proper voltage, but you will 
find when you put the torch all the way up to the sensor (making it full 
of propane) there will be no oxygen there so it will read as if there was 
none.

Interesting what you can come up with in your garage sometimes!

Please don't use your cutting / welding torch on it, the thing isn't 
superman. Notice I said PROPANE.

The best way to change the voltage to a lower voltage would be a resistor 
devider, using 100K or 50K.

If you are going to use a op amp, you need to watch out for NOISE being 
amplified or picked up by the op amp.

Suggest you connect a 1 uf or 10 uf cap like this....


SENSOR ----------RESISTOR---------------------OPAMP INPUT>>>>
                                   |
                               10 uf CAP
                                   |
                                 -----
                                  ---
                                   -

This should filter out any noise, but you have to pick a CAP that will 
allow your computer to read changes within the time you want (meaning a 
10 uf CAP will show changes slower than a 1 uf).

You can also get a pretty good reading in your driveway, at idle. When 
you rev up the car, pumping on the pedal to make it real rich, the 
reading changes quite a bit. Plus you can run a extension cord out to 
your scope! You will also get to see the noise your circuit is picking up.

The people next door might think you are a bit strange, but arn't we all?

Some of these stupid sensors are only one wire, and depend on a chassis 
ground for a return. I added my own ground wire for sense as near the 
sensor as I could.


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