Air/Fuel Ratio guage Circuit

0-1volt at 0.0000001 amps of currents coming from the o2 sensor.
Not much current comes from the o2 sensor,wich can be robbed by some circuits.

Replace to 1meg resistor with a 4.7 meg one.

I have found that the 1 meg resistor will drop the oxygen sensors voltage too much.
Use a 4.7 meg one instead.
You will get the true voltage if not using the 1m resistor at all, but when the oxygen sensor is cold, the circuit freeks out, and neads a resistor.

if not using the 1meg or 4.7 meg resistor, all the leds will light,untill the o2 sensor warms up.


Led brightness will steel voltage from the o2 sensors current and give false readings.You must then adjust for the lower o2 sensor voltage.


Even a digital multimeter will effect the reading slightly.
So even calibrating the circuit with a multimeter, then taking the multimeter off, will give different readings.Good Luck.

I don't use any resistors except for the 4.7 meg that replaced the 1 meg one.

Ok thanks I'll try a bigger resistor as suggested.

But I suspect it may not work, the device was working fine on my test bench and in the truck for a few days and all of a sudden no longer works on the bench or the truck,

It was bench calibrated, I generated a .200v, .500v and .750v signal and adjusted to the proper LED there was no mulimeter connected once the voltage generator was set.

Again thanks for the help (and it worked great and was a good use to us to determine the why the trucks power band was flattening out in the upper RPMS(it was running rich when we thought it was running lean, we rejetted and it's awesome now))

A friend of mine and I just developed a much better 21-LED version of this, using two LM3915's, one in "reverse" so that the logarithmic values line up with the output of the stock sensor. Obviously in no way can the LED's be assigned actual air/fuel ratios, but it can be quite handy for tuning purposes. The meter is setup in a center-weighted bar graph fashion too, so it's very easy to see whether you're rich or lean, and by how much. We also included an op-amp as a high-impedance buffer as not to load down the O2 sensor. The stoich area isn't even measured; the center LED is acutally ON all the time, so that if you're in the stoich area, that single LED is lit. Only the rich/lean areas of the lambda curve are actually measured by the LM3915's.

I'll try to post schematics and maybe even a board layout soon, if there's any interest.

Ken any updates on his circuit I'm curious... I just started rebuilding mine.

You will notice that when the o2 sensor gets hot~very hot, it will not give proper voltage to air-fuel ratio above the 14.7:1 ratio.

Mounting the sensor as far as possible from the exhaust manifold may be benificial.

Well sorry to bump this again.

I rebuilt the circuit as posted in my fist post, I did not add a voltage regulator this time. and used a 4.7k ohm resistor instead of 1 ohm.

It worked for about .5 seconds then something went wrong. I rechecked all my traces and found some were grounding. After fixing this the circuit does not work.

All the traces are good.
There is 12.2 volts to pin 3 and to the LEDs
The Input pin (pin 5) shows whatever Voltage I'm sending to is (say .200v)
The output Pin on the LM3914 show 10.58Volts(all of them) That's not normal is it

Any ideas what's going on? any information you need to help me more. Pretty much going to scrap this project and just buy a damn guage.

Use a 4.7 meg (4,700,000 ohm) resistor !!!, Not 4.7k (4700 ohm).
It will not work if using 4.7k
or, dont use one at all, but then you will have to wait for the sensor to warm up before the sensor will start reading.

dont loose faith.

you dont even nead any resistors in the whole circuit, as the chip is programed to read 1.2 volts when no components are connected to it. eg

Remove all components except for the Leds.
connect pins 2,4 & 8 to ground.
connect pins 3 & 9 to positive.
connect pin 6 to 7.
connect O2 sensors positive signal to pin 5.
connect O2 Sensors negative signal to your circuit's ground.

Thanks Screetch, I abandonned it for the weekend but I'm going to get back at it tonight, will a 10 Meg Ohm resistor work as well?

10meg is the same as not having a resistor at all with this particular circuit.
With a 10meg resistor, the meter will work only when the O2 Sensor has warmed up, ( I know because i tested it).

Any less then 4.7 meg, and it will leak some voltage from the O2 sensor to ground. (meter will show less voltage)


You previously used a 4.7 Kay resistor, and it made all the voltage leak to ground, thats why zero voltage was detected on your air-fuel ratio meter.

HINT FOR ALL: The O2 sensor will ground it's self to it's ground wire when it is warm to hot. the meter freeks out when it's cold because there is no ground. Thats why we put a high ohm resitor to ground(xMega- ohms).

good luck with it Gotrek.

Thanks again screetch at Least now I understand it. Thanks a bunch. Sometimes it sucks just being a soldering monkey.

Like to comment on your teeth,,,LOL THOSE ARE HUGE! I have windows in mine,,the front ones,,,One fell out eating a bigmac about 3years ago,,,with cheeze! as soon as the other brother falls out I am gonna have ONE BIG tooth made to replace the two!

Sorta like my horse's only in ONE right in the front!

Hey! it's better then being a MONKEY "bleeper"

I don't really fully understand what O2 has to do with lean and rich fuel/air mixture.

It takes 16kg of air for 1kg of fuel to burn up with the least amount of O2 and with the cleanest flame.

Measuring fuel flow and intake manifold pressure will be the most accurate method to find out if the mixture is "perfect", "rich" or "lean".

Boncuk

Hi Boncuk,,,"hope I spelled that right". Back in the 70's GM's Caddy had a light bar system that indicated fuel usage as you opened up the venturies in the quadrajet carb. This allowed the driver to at least see where he was waisting fuel and he could back-off or feather his throttle pressure, this would change the amount of mileage one could get out of a tank of fuel imensely. Now we have EFI and ECU's with little one one can do to alter there milage,,EXCEPT,,,,, entering alternative combustables into the system without the control of "BIG COMPUTOR" ie big gov,,ha ha. And by doing so one can then circumvent the programs of the computors demands by various methods.
There are those smart enough to kow how to re-program the ECU comands, but you won't really know you are doing any good by a set command unless you (1) have some form of monitoring the use or WASTE of the fuel and ,,(2) the ability to make adjustments to it accordinly.
See thats why everyone who is on the threads for HHO or PLASMA SPARK TECH are doing. THAT is the reason,,,I who spent 27yrs of my 54yrlife plumbing homes, buisness', hospitals and hotels in tghe middle of the permian basin "West Texas Oil field" where you can't safely consume the water,,,where the water eats the copper, brass, chrome and even Stainless Steel, sometimes within a year from it's use in producing THEE petroleum products, where you shouldn't even shower in it!
Thats WHY I am now attempting electronic knowledge so I can MAYBE just maybe find an alternative fuel so you, I and others can still maintain our normal way of life,,,,without sacrificeing my grandchildrens HEALTH.
SEEEEEEEE?

There is another reason,,, It is the O2 that is measured at the inspection stations for emissions. In California and maybe other States the DPS "STATE COPS", can pull yopu over and require an inspection right on the spot and i starts with a tail pipe emission test and moves from there to visual to see if there have been any ILLEGAL alterations,
"never thought growing up that I'd ever live to see the day where governing bodies could tell you what you could or could not do with something you work for and purchased!"
But here we are, anyway if you fail the test they can impound your vehical for ever if you can't complie.
So emission monitoring is essentuall in this quest.

And of course if you could build one reasonably priced you could sell them to others who can't build um but are trying to monitor there work also. Which would help all of US in funding this quest.

Hello,
The link below might be of interest:
Silicon Chip Online - Using A Wideband O₂ Sensor In Your Car, Pt.1

Regards
Magen

milosman said:

There is another reason,,, It is the O2 that is measured at the inspection stations for emissions. In California and maybe other States the DPS "STATE COPS", can pull yopu over and require an inspection right on the spot and i starts with a tail pipe emission test and moves from there to visual to see if there have been any ILLEGAL alterations,
"never thought growing up that I'd ever live to see the day where governing bodies could tell you what you could or could not do with something you work for and purchased!"
But here we are, anyway if you fail the test they can impound your vehical for ever if you can't complie.
So emission monitoring is essentuall in this quest.

Click to expand...

Get a grip on reality. How would you feel if I burned tires all day or poured poison into a lake.

Boncuk said:

I don't really fully understand what O2 has to do with lean and rich fuel/air mixture.

Click to expand...

Because Oxygen burned is directly related to how lean or rich the fuel mixture is. The less oxygen left means more fuel is in the mix. Or possible bad fuel atomization or distribution, which is essentially the same thing.

It takes 16kg of air for 1kg of fuel to burn up with the least amount of O2 and with the cleanest flame.

Measuring fuel flow and intake manifold pressure will be the most accurate method to find out if the mixture is "perfect", "rich" or "lean".

Click to expand...

No, because manifold pressure does not directly relate to how much air gets in the cylinder. There are far too many variables to account for to 'know' exactly how much mass of air has gotten into the cylinder and then how much has actually burned.

The engine management computer has a map based on load and engine speed to which is a rough estimate of air flow, plus accounting for barometric pressure, air temperature, engine temperature, fast throttle adjustment... If you throw in manufacturing slop, carbon deposits as the car gets older, injectors that do not flow at exact spec or aren't atomizing properly, it's impossible to say that you know the air fuel mixture just given, even the variables that a normal ECU sees unless your in a perfect lab environment.

ECU's try to correct for this over time with trim values based off of the O2 sensor, but anything that the ECU does on it's own is based on 'good enough' fuel mixture, not exact.