Oxygen sensors and automatic mixture control

I have searched high and low but have not been able to find anything on how to build a automated mixture control. As I am building a woodgas generator it would be a big advantage to not have to worry about mixture fine tuning during a run.

Found a way to make a dash gauge to show the output of a sensor here DIY Air / Fuel Ratio Meter

Has any one found a way to do this?


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actually I have a controls engineer working on an engine management system for our turnkey systems. This will use the O2 sensor as it main input but also temps in the reduction zone and vacuum pressure. This system will have servo controlled valves to fine tune things. Its a ways off yet but are working on it.

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Hello Gary and Matt.

I think the automated fuel / air ratio control would be a must on stationary or genset units but for mobile application the manual control works very well. Once the gasifier is up to operating temperature one can run a hopper of fuel ( 50 -100 miles ) without having to make adjustments.

If an air leak develops in the system or if the gasifier begins to plug there needs to be an adjustment . By me making this adjustment it makes me aware of a problem developing .

I believe for mobile use I would first control the fuel / air manually and after a while if not satisfied change it later.

I believe if you polled the drivers they would agree that adjusting the fuel / air manually they are also learning the habits of the gasifier.


Gary , Just read your post again . ( woodgas generator ) Yes auto control for a fuel / air would be important.


Hi Wayne,

Thank you for popping in to comment, I have been following your site and videos for a while and like your down to earth approach.

The aim is to have the generator run up to 6 hours at a time, charging batteries at the same time as powering the house. Other times power is supplied by an inverter with auto transfer, similar to a computer UPS. If there is abnormal temperatures the generator could be shut down, possibly after a time delay to allow for self correction or manual intervention ( like good kick to shake things up).

Hi GaryH
I just read your 2nd post.
If your inverter is like my HD big transformer Trace original it will take a high wattage of direct DC imput. And you say you have batteries to even things out. So . . . if you just engine DC genrate combined you will actually have an engine driven variable speed inverter/charger system just like the most modern consept types from Honda and others
Then the engine RPM and even power can float a high percentage within your six hour batch cycle any gasifier will have.
This frees you up from having to do the eleborate in-process gasifier and engine controls. Your control systems can be stupid simple mechanical then. The “electronics” then are taken care of with “off the shelf” well deveploed tech inside the inverter and a DC alternator charge controller.
Believe me or not, I have gasifier done it both ways and DC charging is the easy get-it-done and move on to the next of Life’s alligator way.
Unless you like being an electron chaser? Me - chased electrons only if I was well paid and then it was just work never fun at all. Fun stuff was after work.
Steve Unruh

Hi, Gary.
I think the project in the link relates to a certain kind of car, a Bentley, and therfore to a certain kind of sensor. It appears to me that there is a BIG difference between a one-wire (unheated, narrow band sensor) and a multi-wire (3 or 4 wires) heated, wide band sensor. Please correct me if i am wrong.
My take on this at present is that you NEED the vehicle’s computer to get a cheap A/F ratio meter to work the one wire sensor, since its rate of output change is so sharp around the “right on” mixture.
i just ordered a Sunpro meter and a CHEAP univeral one-wire sensor to try out, but I will be pleasantly surprised if I can get any useful data from it. I will try to wire it into my arduino datalogger, but I am not sure it’ll work even then without building biasing and cross counting circuits and code.
I’d appreciate anybody out there correcting my thinking.

I want the A/F ratio info to tell me BEFORE my engine governor opens up all the way that something is changing. Not so worried about feeding the info back to some sort of servo control. My problem has been that things SEEM to be going well when my generator is under constant load, (which it almost always is), but I can’t tell that the governor is s-l-o-w-l-y opeing up because my gas quality is dropping until it’s too late to do something about it.

A stationary generator guy,
Pete Stanaitis

Hi Steve,

The generator is a fixed speed 50 HZ 240 volt 5 KVA AC generator. The inverter charges at 30 Amps maximum, trying to run off the inverter only would severely restrict what can be run at times of peak demand. Also as the demand on the inverter would exceed the input at these times and the generator would not be doing any more than 20 % of it’s maximum. The inverter I purchased is capable of running lights, refrigeration, TV and computers. I have run a similar setup before running on diesel worked fine but the fuel costs add up.

Hi Pete,

I have found a number of links to a device called a JAW (just another oxygen sensor) which uses the wide band sensors. Bosch have a lot of technical data online about there sensors, seems the wideband offer quick sensing from a cold start and have a longer life span.

There are references I have found to the JAW being available as a kit. When I find some useful information I will post it here.


Here is the set up I bought to experiment with, It comes with a serial connector for collecting data at well.


We will probably go to a simpler set up and just use the analog signal. As Steve U has said using a DC set up does not need to be over complicated. The better you can isolate loading from the engine the more stable it will be. This system I am working on is for our upcoming larger systems that we will have no choice but to use an AC genhead. I am going oversize these systems quite significantly to make them as stable as possible.

Hi Matt,

I see All Power Labs are using Kubota gas engines that have a higher compression ratio. When I say gas mean gas, not gas as you call it over there. Makes them better suited to wood gas might be worth your while to investigate if you have not done so already.

Ha! Ha! Exellant point on the language confusions Gary Hoffman.
I am constantly tring and encouraging American/Canadians to say and write out gasoline. Some now here have adopted the use of the word petrol - works, for most; but some newbie Americans to engine fueling who have never world traveled.
I tried for a few years to use the word “gasious” for woodgas. Did not work as well as I had hoped. Was too often interpeted as Natural Gas or Propane in areas unlike mine where those are common motor fuels. This same happens a lot with those tring to use the words Producer Gas - confused much again with propane. Well . . . propane to many IS produced in a refinery. LPG = Liquidfied Petroleum (refinery) Gas. I’ve even heard it called formally Refinery Gas to distinguish it from natural gas.
I certainly do not want to be the word nanny!!
I’ll say gasoline and woodgas. And when in any doubt reading ask the correspondent to be sure we are on the same page.
Published info though . . . sometimes I’ve had to read forward and back several times in context to figure out just which fuel “gas” is being presented.
Steve Unruh

Hi Steve,

I imagine there is confusion at times when someone actually wants gas rather than gas. After all petrol is a liquid not gas.

Is Syn Gas a better term for wood gas? Producer gas could also be referring to a Methane gas producer also, the type you put manure into. A few people I have told I am making a wood gasifier say oh you mean a charcoal burner. We know what we are talking about that is all that concerns me.

Hi back GaryH
Syn Gas is a very sticky term also.
I’ve read it used to designate a fossil coal derived combustible made fuel gas versus out of the ground “natural gas”.
Then read this term syngas used as made gasious fuel where only man concentrated oxegen is used in the procees to not have the atmospheric nitrogen carry through as an energy dilution versus Producer Gas made with atmopheric air. Even read Syn Gas used to distiguish man set up thermal-chemically produced fuel gas versus a bacterial/yeast made “Bio-Gas”.
Bio-gas has been used to distinguish all bio-mass derived fuel gasses versus any petroleum (oil from rocks!) “Dino” fuel gases. The modern India developers say “Bio-gas” to distinguish between low temperature biologically made fuel gasses versus high temperature made fuel gases. These they call Bio-Mass gasses.

Yes I agree if your fuel imput stock is wood/woody stems converted to fuel gases by a thremal-chemocal process it truely is WOODGAS.
Charcoal gasifier I have taken to call the output fuel gasses Charcoalgas so others here will know I am distigushing the differences.

That is good enough I think for this site as “Drive (Power) On Wood”.
I do not consider this an “Any bio-mass” gasification site. That confusion is for other sites. Been on six of those prior. It does get very confusing. I’ve now simplfied greatly. Since the only fuel souce I have available to me here in my valley is grown trees - used directly then WOODGAS!
If I charcoal converted my wood first and then gasified that charcoal for motor fuel gases then - CHARCOALGAS.

Do watch out for the word “coal” used also. Fossil coal? For “the black rock that burns” Or charred made from a wood base? I now carfully always try to say/write fossil coal and distictly say c-h-a-r-(red made)c-o-a-l for the other. English as a second language speakers offen say/write “col” or coal for both.

Steve Unruh

Steve Unruh

Hi Gary,

I have looked into the Kubotas, and have decided on using Kohler engines exclusively on the smaller 2kW and 5 kW systems. The Kobota is only offered one or two sizes and would be overkill for these little machines and also drive the cost up. On the 7.5 and 10 kW these will have the Kohler twin liquid cooled direct injected engines. I should have one these to show off soon. These engines will have the “petrol” system still in place on these as a backup fuel source. I have a vendor for these engines as well. Now for the larger 20 kW and larger systems I am using high output GM Vortec engines with 12:1 compression. I don’t know at this point if they will be dual fuel or not. I might look into getting E-85 ready carbs for these systems and offer this as an upgrade for those who have access to this fuel. The reason for the GM engines is they are very easy to get parts for and have a long following of aftermarket parts available for them. I can get these engines remaned very cheap and they more than enough power to get the job done.:slight_smile: Another reason is the 4.3 ltr and 5.7 both share many of the same parts. I have to think as a manufacturer and this helps keep my inventory smaller.

Hi All,

I feel the need to bust an apparent myth because some of us seem to be afraid of electronics. I etched this printed circuit board in my kitchen sink. The two silicone chips here are a frequency to voltage converter and a four chanel amplifier. I made this for a friend to use on his engine dyno. I think YOU guys can figure out simple electronics to automatically control mixture and stuff like that. Why not, you can hack everything else?

I can point you to sources for parts and instructions if you want.

Thank you Rindert, any help you can provide in the way of a circuit would be appreciated. I have made boards myself in the past also but have never learnt how to design a circuit.

Megasquirt is the answer here I think.


I have been thinking I would use the electric choke control from an old Toyota to move a butterfly valve. Your thoughts?

Hi Rindert,

Thanks again for the input, how will one of these work with vacuum against the butterfly. Will it drift due to the spring arrangement? My thought was to use a servo motor from a remote control plane as they will stay in the same position as long as there is no power applied to the motor.

Still how ever the big challenge is the electronics, Thanks Jim Radcliffe I have been looking at http://www.megasquirt.info/, have not had time to fully investigate it as yet. As it can control ignition timing also would be useful for those converting late model electronically controlled engines in vechiles. May be a big help for someone who is fitting spark plugs to a Diesel engine.

Hi Gary,

Your servo motor will work. A lot of automobiles use those for similar applications. I’m thinking the electronics needed to feed current to that coil type choke control will be very simple, Just a Pulse Width Modulated circuit with input from the Oxygen Sensor determining the pulse with. Is you servo easy to cotrol? How?