J
JazzMan
- Jan 1, 1970
- 0
John said:Hello All,
I'm pretty new to electronics and would like to take this chance to learn
more about electronics and at the same time create a useful gadget.
I would like to create an A/F (air/fuel display). Here are some of the
constraints, notes, and parts that will be used for this project.
-- air/fuel mixture will be fed from the O2 (oxygen sensor) located at the
header (it's for a 92 civic dx).
-- O2 sensor provides 0-1V
-- would like to use an LCD display of some type with 3 digits
-- would like to display the actual voltage provided by the O2 sensor in
millivolts up to three decimal places
e.g. O2 sensor reads 0.15V, I would like my A/F meter to display a
reading of 150
-- would prefer not use a PIC since I don't have a PIC writer (i can program
in assembly)
Later on would like to add three leds, one red, one green, one yellow...
red=volts<0.2V, green=0.8>volts>0.2, yellow=volts>0.8V... this would be a
quick glance indicator of what's the current status of the A/F mixture
without having to read the actual display.
I'm looking for any suggestions as to what components to use and how to
build this project. Also, any reading that might help me learn more about
electronics while building this project would be helpful.
Thanks!
John
Some issue to consider. Most O2 sensors are non-linear, which means that
the voltage they put out is not proportionate to the amount of O2 in
the exhaust stream. As a result, almost all cars using standard-type
O2 sensors use them as rich/lean switches rather than actually trying
to measure the amount of exhaust O2. Another issue is that the measuring
device need to have very high input impedence, otherwise there is a very
real chance of damaging the sensor permanently.
You mentioned that it's a Honda? If it has the V-TEC engine then your
O2 sensor is of a type referred to as a Wide Band O2 sensor. This kind
of sensor is designed to measure O2 directly and within a fairly wide
range of fuel/air mixtures. This kind of sensor requires special control
circuitry because it's heated, among other reasons. It is a fairly
advanced project to try designing for a wideband sensor, it would be
much easier to just buy either a kit or an assembled unit.
Back to the regular sensor. Outside of the stochiometric ratio of 14.7:1
where the O2 sensor voltage is 450mV the voltage is not really
meaningful.
JazzMan
--
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