Averaging 2 0-5V analog signals

Thread Starter

Jawesome1

Joined May 26, 2021
9
Hello.
I’m brand spanking new here, and looking for assistance.

I’m looking to build a semi-simple circuit/module that will combine the outputs of 2 Mass Air Flow sensors (MAFs) and average them for the ECU.

It’s for a simple electronic fuel management piggyback device.

Basics are:
Two MAFs, two turbos, common plenum, and fuel injectors with exactly twice the stock flow rating.

By splitting the MAF signal in half (effectively) the ECU cuts the injector duty cycle in half (so fuel flow matches what it should be for the given amount of air flow)

I Would also like to have an output adjustment (+/-20%) for tweaking.

I found this thread:
https://forum.allaboutcircuits.com/threads/averaging-two-0-5v-analog-signals.9620/

It starts out good, but gets overly complicated toward the end by addin other components.

I just want to alter the ECU inputs to get the desired result, like we’ve been doing for years.

I’m a fabricator, not an electrician, but I can read simple schematics and build circuit boards. I’ve built many turbo setups, and used a multitude of different methods to control the mixture (FMUs, rechipped ECUs, Apexi Super-AFCs, aftermarket ECUs, etc.) I feel the factory ECU is the best controller out there, it just needs fooled a bit (or byte! Lol)

Thanks in advance for any input!!
J-
 

andrewmm

Joined Feb 25, 2011
1,496
What you "need" is to add the two signals together,
and divide by two

A virtual earth summing amp will do the first,
a resistor divide , either on the summer or separate does the divide by two,

BUT

Engine bays are a horrible environment,
high and low temperatures, oil / water, very un reliable power for the circuit, and lots of shock and vibration,

Can you give us some idea as to the final use of this please,
i.e. if it goes wrong , what are the consequences ?
 

BobaMosfet

Joined Jul 1, 2009
1,780
Hello.
I’m brand spanking new here, and looking for assistance.

I’m looking to build a semi-simple circuit/module that will combine the outputs of 2 Mass Air Flow sensors (MAFs) and average them for the ECU.

It’s for a simple electronic fuel management piggyback device.

Basics are:
Two MAFs, two turbos, common plenum, and fuel injectors with exactly twice the stock flow rating.

By splitting the MAF signal in half (effectively) the ECU cuts the injector duty cycle in half (so fuel flow matches what it should be for the given amount of air flow)

I Would also like to have an output adjustment (+/-20%) for tweaking.

I found this thread:
https://forum.allaboutcircuits.com/threads/averaging-two-0-5v-analog-signals.9620/

It starts out good, but gets overly complicated toward the end by addin other components.

I just want to alter the ECU inputs to get the desired result, like we’ve been doing for years.

I’m a fabricator, not an electrician, but I can read simple schematics and build circuit boards. I’ve built many turbo setups, and used a multitude of different methods to control the mixture (FMUs, rechipped ECUs, Apexi Super-AFCs, aftermarket ECUs, etc.) I feel the factory ECU is the best controller out there, it just needs fooled a bit (or byte! Lol)

Thanks in advance for any input!!
J-
@Jawesome1 We need more.

  1. What kind of signal does the MAF generate? PWM, DC, AC...?
  2. What voltages are involved with the MAF signals?
  3. How do you want it to fail if something goes wrong, to avoid damage? (@andrewmm - good thinking)
 

Thread Starter

Jawesome1

Joined May 26, 2021
9
What you "need" is to add the two signals together,
and divide by two

A virtual earth summing amp will do the first,
a resistor divide , either on the summer or separate does the divide by two,

BUT

Engine bays are a horrible environment,
high and low temperatures, oil / water, very un reliable power for the circuit, and lots of shock and vibration,

Can you give us some idea as to the final use of this please,
i.e. if it goes wrong , what are the consequences ?
Thanks for the reply!
Adding 2 values then dividing by 2 is exactly what averaging is! lol

Unit would live in dash/glovebox. Shielded cables to MAFs and to ECU. Power supplied from main chassis fuse panel. Pot adjustment onboard (+/- 20%).

Final use is exactly as described. Halfing the (double-sized) MAF signal to get a Halfed signal to the (double-sized) injectors.
It will likely need some kind of onboard voltage regulation.
and the output signal to ECU must never exceed 5vdc, even if adjusted to +20%.

If it fails, the ECU ‘sees’ NO MAF, and goes into limp mode.
If one MAF fails, the engine will run like garbage since the mixture is out of whack. Mixture will be monitored in real-time via gauge.

I’ve got the car stuff taken care of, I just need a schematic and a parts list (preferably).
Here are two schematics from the previous thread, but seems the components are outdated and I need.

Thanks again
 

Attachments

Thread Starter

Jawesome1

Joined May 26, 2021
9
@Jawesome1 We need more.

  1. What kind of signal does the MAF generate? PWM, DC, AC...?
  2. What voltages are involved with the MAF signals?
  3. How do you want it to fail if something goes wrong, to avoid damage? (@andrewmm - good thinking)
Hello!

MAF uses 12vdc power
Generates 0-5vdc output
Analog

ZERO output to ECU would trigger ‘limp-mode’ and be the safest bet
 

andrewmm

Joined Feb 25, 2011
1,496
Thanks for the reply!
Adding 2 values then dividing by 2 is exactly what averaging is! lol

Unit would live in dash/glovebox. Shielded cables to MAFs and to ECU. Power supplied from main chassis fuse panel. Pot adjustment onboard (+/- 20%).

Final use is exactly as described. Halfing the (double-sized) MAF signal to get a Halfed signal to the (double-sized) injectors.
It will likely need some kind of onboard voltage regulation.
and the output signal to ECU must never exceed 5vdc, even if adjusted to +20%.

If it fails, the ECU ‘sees’ NO MAF, and goes into limp mode.
If one MAF fails, the engine will run like garbage since the mixture is out of whack. Mixture will be monitored in real-time via gauge.

I’ve got the car stuff taken care of, I just need a schematic and a parts list (preferably).
Here are two schematics from the previous thread, but seems the components are outdated and I need.

Thanks again


I was asked about what happens if this goes wrong as you are driving, does the engine die or does it destroy the engine,
what happens , does the car crash, i.e. is this safety critical ?
 

Thread Starter

Jawesome1

Joined May 26, 2021
9
I was asked about what happens if this goes wrong as you are driving, does the engine die or does it destroy the engine,
what happens , does the car crash, i.e. is this safety critical ?
sorry. I’ll elaborate on my third paragraph.
limp mode is a predetermined safe operation mode that restricts rpm, but allows the car to continue down the road.

Engine or car damage is up to the driver. And bad drivers don’t need turbos!


Other than that, there is no relevance.

thanks
 

Thread Starter

Jawesome1

Joined May 26, 2021
9
If the MAF input impedance is high enough, all you would need are two equal value resistors tied to the MAF input.
The MAF pulls power straight from the battery. Idk the impedance off the top of my head, but I don’t believe it’s relevant. Only the 0-5vdc signal. It’s analog, and voltage only, no waves or PCM or anything like that.

I don’t believe 2 resistors would get the functionality I need (especially the adjustment)

thanks
 

Thread Starter

Jawesome1

Joined May 26, 2021
9
It is if you just use just the resistors.
You can make one a variable resistor (pot).
hmmm... could you make a sketch/schematic showing the two MAFs?

The injectors are 12-13ohms.
idk the MAF right now (at work), but could you ‘assume’ the same 12-13 for illustration purposes? And then we can alter it later after I measure

thanks!
 

LowQCab

Joined Nov 6, 2012
588
The MAF Sensors are Mechanical/Electrical Sensors.
They have a "Curve" which is compensated for by a Trim-Table(s) in the ECU.
That Trim-Table will be incorrect after you physically move the location of the MAF Sensor.
Unless you just dump really excessive amounts of Fuel into the Engine,
You will have Rich and Lean areas of operation,
This is very dangerous in a Boosted application, and can easily result in the Engine
getting into a hard Detonation condition which may blow-out Head-Gaskets, (if you're lucky),
or MELT PISTONS if you're not lucky.

You need Tuning-Software such as "HP-Tuners" to re-Tune the MAF-Trim-Table(s)
after moving the MAF-Sensor physical location,
and, altering the minimum and maximum Air-Flow-Volume.

Many other ECU Tables will need to be modified as well,
not the least of which is the Ignition-Timing-Map.

You will also need a 2 or 3-Bar MAP-Sensor,
and the appropriate ECU Firm-Ware Up-Grade to
allow the new MAP Sensor to function correctly.

Without these items, and the knowledge and experience to set them up correctly,
You are going to destroy an expensive Engine.

Here is what you need to destroy your Engine ...........
.
.
.
MAF Combiner FLAT .png
 

Thread Starter

Jawesome1

Joined May 26, 2021
9
The MAF Sensors are Mechanical/Electrical Sensors.
They have a "Curve" which is compensated for by a Trim-Table(s) in the ECU.
That Trim-Table will be incorrect after you physically move the location of the MAF Sensor.
Unless you just dump really excessive amounts of Fuel into the Engine,
You will have Rich and Lean areas of operation,
This is very dangerous in a Boosted application, and can easily result in the Engine
getting into a hard Detonation condition which may blow-out Head-Gaskets, (if you're lucky),
or MELT PISTONS if you're not lucky.

You need Tuning-Software such as "HP-Tuners" to re-Tune the MAF-Trim-Table(s)
after moving the MAF-Sensor physical location,
and, altering the minimum and maximum Air-Flow-Volume.

Many other ECU Tables will need to be modified as well,
not the least of which is the Ignition-Timing-Map.

You will also need a 2 or 3-Bar MAP-Sensor,
and the appropriate ECU Firm-Ware Up-Grade to
allow the new MAP Sensor to function correctly.

Without these items, and the knowledge and experience to set them up correctly,
You are going to destroy an expensive Engine.

Here is what you need to destroy your Engine ...........
.
.
.
View attachment 239723
Thanks!
This was almost like it was 1998 and I was reading “maximum boost” by Corky Bell again, with the exception of ‘Corky’s Rules’.

Yeah, some of that info still holds true 25 years later, and experience has proven that some don’t. Thanks for the info though!

Anyway, so this schematic will do all the things I’ve asked? I’ll have to take your word on that because that’s where I lack the knowledge and that’s why I’ve been very specific about what I’m looking for. And thats also why I’m here!

I have solutions for everything I need, however, instead of pulling the MAF sensor out of the MAF housing and sticking it into a tube with twice the cross sectional area(for the twice sized injectors) , I feel using two MAFs would be more accurate.
This works fine to compensate for injectors that are 30-50% larger than stock, but 200% would make a pretty good size pipe, and the sensor would not protrude into as far as I feel it should.

Typically, as long as the MAF is at least 12” from Throttle Body or Turbo the airflow is smooth enough to function well. They aren’t too picky as long as they aren’t tilted up or down hill more than 40-ish degrees, and the electronics are oriented to the top as much as possible.

Modern factory ECUs are way smarter than most aftermarket ECUs. Plus, they allow SO MANY creature comforts to improve the quality of the ride. Using Closed-loop operation and wide band Oxygen sensors, along with multiple knock sensors, they learn what they need to know.

I’m not saying this is true of ALL manufacturers, but they don’t all matter either!

So, is this circuit designed to destroy my engine? Or is it designed to perform the way I’ve asked?☺

thanks again!
 

LowQCab

Joined Nov 6, 2012
588
It will do precisely what you requested,
but that doesn't mean that it's going to be "Plug-N-Play" in the real World.

2- things that you have not taken into consideration are ..........
The MAF Sensors may "see" a different Pulsation/Reversion Pattern in the Air-Flow
which will alter their outputs and accuracy to "some" unknown degree.

And, as the Air-Volume is now cut in half under normal Idle and Cruise conditions,
the resolution/accuracy of their outputs may be unacceptable.

But, of course, you could get lucky, and these things may not be a big problem.
The thing is, YOU NEED TO KNOW whether they actually DO create a problem, or not.

As for operational features .......

1) The design has it's own protected 5V- Voltage-Regulator,
so as to not place any additional load on the ECU's 5V power-supply.
( Note that ALL GROUNDS must be connected at ONE-POINT to
the existing ECU-Signal-Ground-Wire intended for the original MAF-Sensor ).
Grounds from different various locations may cause unknown problems.

2) Extensive Noise Filtering at every Stage of the Circuit.

3) Low Impedance Output, strictly limited to between true zero-volts, and a full 5-Volts.

4) Op-Amp with stable "Rail-to-Rail" Input and Output Voltage capability,
and a strong, relatively High-Current-Output capability.

5) All 0.5% Precision Resistors, (with 2 exceptions which are not critical to operation ).

6) Plus-or-Minus ~5% Output-Offset adjustment, if required.
( this is a very cheezy and sloppy way to "tune" an Engine )
This value must be set to zero before initial operation.
To do this, Ground one MAF Input, then connect the other MAF Input to the 5-V Supply.
This should create precisely 2.50-Volts at the Output,
when the Multi-Turn-Trimpot is roughly at its center position.
This Voltage can also be measured at the "Wiper" Pin of the Trimpot.
Remember that the output of the MAF Sensors will probably operate between ~2-V and 4-V.
That's only a ~2-Volt swing between Idle and WOT.

7) No critical layout or construction requirements.
Can be built on a standard project "Perf-Board" with only 2- 8-Pin IC-Sockets,
making Op-Amp and V-Regulator replacement very easy if you smoke them.

8) The only "Special" connection is a switched 12-V, 5-A Power source.
( the Circuit its self draws a very tiny Current,
and could even be permanently connected to the Battery, but that's not recommended )

Good Luck.
 

Thread Starter

Jawesome1

Joined May 26, 2021
9
It will do precisely what you requested,
but that doesn't mean that it's going to be "Plug-N-Play" in the real World.

2- things that you have not taken into consideration are ..........
The MAF Sensors may "see" a different Pulsation/Reversion Pattern in the Air-Flow
which will alter their outputs and accuracy to "some" unknown degree.

And, as the Air-Volume is now cut in half under normal Idle and Cruise conditions,
the resolution/accuracy of their outputs may be unacceptable.

But, of course, you could get lucky, and these things may not be a big problem.
The thing is, YOU NEED TO KNOW whether they actually DO create a problem, or not.

As for operational features .......

1) The design has it's own protected 5V- Voltage-Regulator,
so as to not place any additional load on the ECU's 5V power-supply.
( Note that ALL GROUNDS must be connected at ONE-POINT to
the existing ECU-Signal-Ground-Wire intended for the original MAF-Sensor ).
Grounds from different various locations may cause unknown problems.

2) Extensive Noise Filtering at every Stage of the Circuit.

3) Low Impedance Output, strictly limited to between true zero-volts, and a full 5-Volts.

4) Op-Amp with stable "Rail-to-Rail" Input and Output Voltage capability,
and a strong, relatively High-Current-Output capability.

5) All 0.5% Precision Resistors, (with 2 exceptions which are not critical to operation ).

6) Plus-or-Minus ~5% Output-Offset adjustment, if required.
( this is a very cheezy and sloppy way to "tune" an Engine )
This value must be set to zero before initial operation.
To do this, Ground one MAF Input, then connect the other MAF Input to the 5-V Supply.
This should create precisely 2.50-Volts at the Output,
when the Multi-Turn-Trimpot is roughly at its center position.
This Voltage can also be measured at the "Wiper" Pin of the Trimpot.
Remember that the output of the MAF Sensors will probably operate between ~2-V and 4-V.
That's only a ~2-Volt swing between Idle and WOT.

7) No critical layout or construction requirements.
Can be built on a standard project "Perf-Board" with only 2- 8-Pin IC-Sockets,
making Op-Amp and V-Regulator replacement very easy if you smoke them.

8) The only "Special" connection is a switched 12-V, 5-A Power source.
( the Circuit its self draws a very tiny Current,
and could even be permanently connected to the Battery, but that's not recommended )

Good Luck.
.
.
,
Wow!
You’ve been very thorough with everything. I greatly appreciate that!

Thanks so much!
- J
 
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