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Nitramrebrab72
Samba Member
Joined: November 10, 2018
Posts: 1036
Location: France
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 Posted: Thu Dec 04, 2025 4:06 am Post subject: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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https://www.ebay.co.uk/itm/172343718358
Looking at making a AFR reader from an analog voltmeter and broadband lambda sensor from a scrapped car.... |
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jeffrey8164
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Joined: January 06, 2018
Posts: 4239
Location: Georgia
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| Posted: Thu Dec 04, 2025 8:49 am Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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Let us know how it goes.
I used the PLX set up with Bluetooth to my phone since I didn’t feel like ripping the interior apart to run wires.
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Nitramrebrab72
Samba Member
Joined: November 10, 2018
Posts: 1036
Location: France
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| Posted: Thu Dec 04, 2025 9:28 am Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| I am going to remove the backround dial ,out and colour the 0.4-0.6volts range with a green tint and a tall white line in the middle at 0.5v and 0.6v-0.7/0.4-0.3 yellow 0.3-.02/0.8-0.9 orange and the rest red. |
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panel
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Joined: December 02, 2001
Posts: 1232
Location: Victoria B.C. Canada
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NJ John
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Joined: September 21, 2007
Posts: 3076
Location: HdG, MD & NJ
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| Posted: Thu Dec 04, 2025 3:54 pm Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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I’ve done it. It work’s. I never used it for tuning. Narrow band will drive you crazy.
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Rubix12345
Samba Member
Joined: February 14, 2023
Posts: 18
Location: USA
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| Posted: Thu Dec 04, 2025 4:50 pm Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| You can grab a proper wideband for $75-100 on ebay or amazon. Just do that. |
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Nitramrebrab72
Samba Member
Joined: November 10, 2018
Posts: 1036
Location: France
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| Posted: Thu Dec 04, 2025 7:44 pm Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| I believe the wide band is actually 5 volts , so I can use a scrapped 6 volt gauge..So could be possible to make one from lying around gathering dust parts.. |
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Bugsy61
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Joined: March 20, 2011
Posts: 273
Location: Peoria, Illinois
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| Posted: Thu Dec 04, 2025 8:25 pm Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| You can use any volt meter with a low range, and a narrow band oxygen sensor. I used one back in 1998, 1999 when wide bands were way expensive. The needle bounces around so much it is tough to make sense of. Just bite the bullet and buy a wide band test set up. You'll use it for decades to come. It is a great investment in your future projects. |
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Nitramrebrab72
Samba Member
Joined: November 10, 2018
Posts: 1036
Location: France
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| Posted: Fri Dec 05, 2025 3:23 am Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| Bugsy61 wrote: |
| You can use any volt meter with a low range, and a narrow band oxygen sensor. I used one back in 1998, 1999 when wide bands were way expensive. The needle bounces around so much it is tough to make sense of. Just bite the bullet and buy a wide band test set up. You'll use it for decades to come. It is a great investment in your future projects. |
It's not a money thing, I spend a lot of time with financially poor people, but very rich in knowledge ,joy and happiness making things from nothing which I now enjoy doing , the other thing is I burn mixed fuels depending what I can find in the country I'm in Europe right down to Africa alcohol/petrol/light oils so I am looking for the stoichimetry of the burnt mixture as quite often I don't know what mixture of fuel I am burning so the AF ratio is little help without knowing the exact composition of the fuel . ...
As you say it bounces a lot that means an inertia weighted needle voltmeter is required or maybe was it down to the narrow band lambda sensor  |
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tencentlife
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Joined: May 02, 2006
Posts: 10164
Location: Abiquiu, NM, USA
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| Posted: Fri Dec 05, 2025 8:07 am Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| Quote: |
| making things from nothing |
Well if you can make a wideband controller from nothing I'd say you have a new career in front of you.
Without a controller, though, good luck getting any output of any voltage out of a wideband O2 sensor.
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mikedjames
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Joined: July 02, 2012
Posts: 3477
Location: Hamble, Hampshire, UK
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| Posted: Fri Dec 05, 2025 9:00 am Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| Nitramrebrab72 wrote: |
| I believe the wide band is actually 5 volts , so I can use a scrapped 6 volt gauge..So could be possible to make one from lying around gathering dust parts.. |
Measure the DC resistance of the 1 volt meter. Connect a resistor that is exactly 4 times larger in value in series with it. And now when 5 volts is across the series connection of the resistor and meter, it will draw the same current as 1 volt across only the meter.
And there you have a 5 volt meter.
In fact all those moving coil meters are current meters, with a resistor in series to turn them into volt meters. If you know the max current for full scale, Ohms law will tell you the resistor you need to make a volt meter. (full scale voltage) divided by (full scale current) = total resistance.
Of course the meter movement itself has a resistance, that limits the lowest voltage you can measure - I think my 1mA meter has a resistance of 75 ohms so the lowest voltage it can measure is 0.075V.
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DesertSasquatchXploration
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Joined: April 16, 2021
Posts: 1082
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| Posted: Fri Dec 05, 2025 9:34 am Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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Already been over this many times use your multimeter set to mV and a o2 sensor one wire. 1v is rich .100 is lean.
You first get in the ballpark the old school way.
https://www.aircooled.net/vw-carburetors-jetting-102/
The AFR gauge is for fine tuning
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Nitramrebrab72
Samba Member
Joined: November 10, 2018
Posts: 1036
Location: France
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| Posted: Fri Dec 05, 2025 12:02 pm Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| mikedjames wrote: |
| Nitramrebrab72 wrote: |
| I believe the wide band is actually 5 volts , so I can use a scrapped 6 volt gauge..So could be possible to make one from lying around gathering dust parts.. |
Measure the DC resistance of the 1 volt meter. Connect a resistor that is exactly 4 times larger in value in series with it. And now when 5 volts is across the series connection of the resistor and meter, it will draw the same current as 1 volt across only the meter.
And there you have a 5 volt meter.
In fact all those moving coil meters are current meters, with a resistor in series to turn them into volt meters. If you know the max current for full scale, Ohms law will tell you the resistor you need to make a volt meter. (full scale voltage) divided by (full scale current) = total resistance.
Of course the meter movement itself has a resistance, that limits the lowest voltage you can measure - I think my 1mA meter has a resistance of 75 ohms so the lowest voltage it can measure is 0.075V. |
Now thats quite useful for my little project.. Thank you... |
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2pist
Samba Member
Joined: July 03, 2022
Posts: 1
Location: GA
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| Posted: Wed Dec 10, 2025 5:07 pm Post subject: Re: Is it possible to make an AirFuel Ratio meter for under 10$??? |
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| I was thinking about a wideband diy too. I would use an Arduino to output the voltage to 2 lm 3914 linear LED drivers. That would give you 10 led resolution. It would be easy to scale. Somebody made a shield over in England and attempted to make a business but things are quiet over there now. |
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