Air/Fuel Mixture Meter

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

John wrote:

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
--
************************************************** ********
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
************************************************** ********
"Rats and roaches live by competition under the laws of
supply and demand. It is the privilege of human beings to
live under the laws of justice and mercy." - Wendell Berry
************************************************** ********

"JazzMan" <No_Spam@airmail.net> wrote in message
news:4265D4A7.1272@airmail.net...

John wrote:

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

It's not a wideband sensor. It's the regular type on a non-vtec engine
(D15B7).

Are there any good articles on Honda sensors or regular sensors in general?

Why doesn't the regular O2 sensor measure linearly? Also, would an A/F meter
like the one I'm planning for a regular O2 sensors be of any use? I think it
would definitely be an interesting project to work on even if it's not as
accurate.

Also, what do you mean by "having a high impedance input" as far as the
meter goes?

Thanks!

John

"John" <welcomehowcome@hotmail.com> wrote in message
news:wISdnXDx5aSUQfjfRVn-qw@comcast.com...

"JazzMan" <No_Spam@airmail.net> wrote in message
news:4265D4A7.1272@airmail.net...
John wrote:

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

It's not a wideband sensor. It's the regular type on a non-vtec engine
(D15B7).

Are there any good articles on Honda sensors or regular sensors in
general?

Why doesn't the regular O2 sensor measure linearly? Also, would an A/F
meter
like the one I'm planning for a regular O2 sensors be of any use? I think
it
would definitely be an interesting project to work on even if it's not as
accurate.

Also, what do you mean by "having a high impedance input" as far as the
meter goes?

Thanks!

John

Hmm.. high input impedance... I think I know what you mean. If the measuring
device has low impedance, the current might flow towards the sensor instead
of the metering device which might damage the sensor, is this what you mean?

Well, from my basic understanding of electronics, I was thinking I could
grab a very small sample from the sensor signal and amplify it with a
transistor at my meter side. So basically, I could place a high resistor
value in parallel with the signal which would drive the transistor and by
amplified for the meter to read and display. But then again, the transistor
will require at least 0.7V in order to open up (I think saturate is the
proper term here) which is pretty much what the O2 signal can provide. So
how do I go about making this work without inversing the flow of current and
damaging the O2 sensor?

Thanks!

John

John,

high input impedance means that as far as the sensor is concerned it sees a
high resistance from whatever it is connected to. If you connect that O2
sensor to a low impedance circuit you reduce the output voltage, this can
affect the operation of the cars ECU as that now sees a lower than expected
voltage and so compensates by altering the fuel/air mixture.

There are several high input impedance circuits out there on the net you can
use, you can buy high impedance single rail supply op-amps which would be
ideal for this circuit. You would use one to buffer the circuit (and so
prevent interfering with the cars ECU operation) and then another (normal
op-amp) as a non-inverting amplifier to boost the signal before feeding it
into the digital meter. Although you could also do this by butchering a high
imput impedance DVM!

Chris

"Chris Dugan" <chrisdotdugan@bloodyobvious.co.uk> wrote in message
news:4jw9e.13636$DU6.8705@newsfe1-gui.ntli.net...

John,

high input impedance means that as far as the sensor is concerned it sees
a
high resistance from whatever it is connected to. If you connect that O2
sensor to a low impedance circuit you reduce the output voltage, this can
affect the operation of the cars ECU as that now sees a lower than
expected
voltage and so compensates by altering the fuel/air mixture.

Yeah, it's making sense now. I think you said pretty much what I said the
post after. So that's definitely a good thing :-)

There are several high input impedance circuits out there on the net you
can
use, you can buy high impedance single rail supply op-amps which would be
ideal for this circuit. You would use one to buffer the circuit (and so
prevent interfering with the cars ECU operation) and then another (normal
op-amp) as a non-inverting amplifier to boost the signal before feeding it
into the digital meter. Although you could also do this by butchering a
high
imput impedance DVM!

Chris

Could you give a little more detail as to how a high impedance buffer works
and what components/ideas are behind it?

Based on your description, I think that's exactly what I need. So basically
I tap into the O2 sensor signal somewhere between the O2 and the ECU, and
use that as the input to the buffer? As far as the display goes, how would I
convert that tiny voltage/current(say 0.50mV) to display as 500 on a digital
display? And what display would work for this meter/gauge gadget I'm working
on?

Thanks!

John

John

Try this link it gives a pretty good overview about op-amps and their uses:

http://www.answers.com/topic/operational-amplifier

The specific sections you want are voltage follower, difference amplifier
and non-inverting amplifier. The voltage follower acts as a buffer and
provides no signal amplification (called gain) or you can use a difference
amplifier circuit. Which would give you a variable output depending on the
difference in voltage between the two inputs (this can be an advantage in an
electrically noisy environment such as a car as it means that any common
noise signal in both the ground and signal wire gets ignored and your
voltage reaching your display will be more stable).

The final part is to use a non inverting amplifier to boost (or multiply by
the gain factor) the input signal: e.g for a gain of 6 your 0-2v sensor
voltage would vary between 0 and 12V provided the op-amp can push the output
to the power supply limits (not all of them can). You're probably better off
staying with a 2V range and using a digital panel meter calibrated for a max
reading of 2V then allmost all your resistors in the amplifiers will be the
same value. It's better to keep the signal going to the display at a
reasonable level rather than reducing to your 500mv as noise will tend to
drown out the signal at that level (think of an old audio amplifier - the
noise level is pretty much the same and at low volume levels it almost
drowns out the music).

For the 3 Red, Green, Yellow LED's you can use three op-amp comparators all
reading the same signal and just referenced to different voltages. So that
op-amp 1 turns on at 0V op-amp2 at 0.2V etc or you can get a bar graph chip
(LM3916 from National Semiconductor) and connect LED's only to 3 outputs,
calibrating the chip so the LED's are at the switching points.

For any further circuits just do a google for op-amp schematics or have a
look at a few manufacturers website for application notes, you'll then learn
about decoupling capacitors and voltage regulators which you'll need as
well.

As for specific devices to use everybody has their favourites; National,
Maxim etc. and if I told you everything to do there'd be nothing for you to
work out for yourself would there ;-) Half the fun with electronics is
learning from your mistakes and learning to keep the magic smoke inside the
components!

Chris

--FWIW there was a neat widget for sale in gag shops a few
years back called the "Fart detector". It consisted of a battery
powered heated grid; I think the technical term for this is a hot pipe
anemometer. Anyway, when confronted by something other than air the
cooling rate of the device would change; this condition caused a
recording to play. Accompanied by siren whoops it would shout:
"Warning! Fart detected!" I extended the probe wires and stuck one
inside the combustion chamber of a potato gun, trying to sense when the
mixture was right for firing. Results not great, but it made for an
interesting project, heh.
--The trick is not so much to detect a mixture, but to detect
the *right* mixture. Still workin' on that one...


--
"Steamboat Ed" Haas : For some reason hung up on
Hacking the Trailing Edge! : Mexican Oompah bands...
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---

"John" <welcomehowcome@hotmail.com> schreef in bericht
news:v-ydnYfgyqniTfjfRVn-1g@comcast.com...

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.

Maybe this page is of interest to you.

http://www.ronsoft.nl/index.php/153

Jeroen

John wrote:

"Jeroen" <none@none.com> wrote in message
news:42691b5b$0$98488$e4fe514c@news.xs4all.nl...

"John" <welcomehowcome@hotmail.com> schreef in bericht
news:v-ydnYfgyqniTfjfRVn-1g@comcast.com...
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.


Maybe this page is of interest to you.

http://www.ronsoft.nl/index.php/153

Jeroen

Excellent! Thank you!

That's what I was looking for--nice explanation with a schematic.

John

Here's a kit that I'm contemplating buying:

http://wbo2.com/

Comes highly recommended.

JazzMan
--
************************************************** ********
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
************************************************** ********
"Rats and roaches live by competition under the laws of
supply and demand. It is the privilege of human beings to
live under the laws of justice and mercy." - Wendell Berry
************************************************** ********