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-   -   Instead of vacuum gauge: multimeter on MAP sensor (https://ecomodder.com/forum/showthread.php/instead-vacuum-gauge-multimeter-map-sensor-6466.html)

MetroMPG 12-18-2008 10:42 AM

Instead of vacuum gauge: multimeter on MAP sensor
 
Just had a thought - probably not original:

Instead of buying a vacuum gauge, another option is to wire a cheap multimeter to the MAP (manifold absolute pressure) sensor (if your car has one).


It wouldn't be too hard to drive a little bit and see what voltage corresponds to the lightest load, then use it as a relative indicator of fuel consumption. Very useful if using the DWL (driving with load) technique.

Maybe make a simple LED array that does the same thing, so you don't have to read numbers.

MazdaMatt 12-18-2008 11:21 AM

wasn't there some talk recently of MAPs having a frequency output as opposed to V output?

Daox 12-18-2008 11:26 AM

Most MAPs have voltage outputs. I'm sure some maker somewhere thought they'd be smart and put in a frequency output on something though.

MetroMPG 12-18-2008 12:09 PM

Quote:

Originally Posted by MazdaMatt (Post 79215)
wasn't there some talk recently of MAPs having a frequency output as opposed to V output?

Right - joelmaldonado used a Ford frequency output MAP sensor for his load-smart cruise control: http://ecomodder.com/forum/showthrea...html#post68043

And I just remembered where else I've seen a MAP sensor + multimeter as instrumentation: http://ecomodder.com/forum/showthrea...p-off-601.html

Ironically, they were using a Ford, so bought a junkyard GM MAP sensor to take relative readings of engine load during their tests.

tasdrouille 12-18-2008 12:42 PM

TDI MAPs are 0-5v. But then again we don't run under vac. It's useful to get the load though.

dcb 12-18-2008 12:45 PM

I took some readings off the metro map sensor that coyotex sent. I used an atmega168 to turn 5 volts into a 0 to 1023 number, but a voltmeter on 5 volt scale would do fine too (for a geo):
http://ecomodder.com/forum/showthrea...nsor-5208.html

I really have no idea how many cars use pulses vs sensors or what all the pinouts are or the signals or voltages involved might be though.


Oh, and an analog meter would be nice for vacuum.

almightybmw 12-19-2008 03:13 AM

I "think" my 95 sonoma has a map sensor. Anyone confirm? 4.3 CPI motor(92-95), not TBI or CFSI (96+ only).

I don't think the GP has one though, and that's my highway cruiser.

wikityler 12-19-2008 03:19 AM

I did this with my acclaim. I found that the dmm I was using, having 1/2 second measurement, wasn't responsive enough. Something a bit faster, and it would work great.

dichotomous 12-19-2008 12:43 PM

I like this idea, one two wire cord coming into the cabin and my multimeter would make a good proof of concept and load indicator, very nice idea, I will likely try this sometime this weekend

MetroMPG 12-19-2008 12:53 PM

Cool - let us know how it goes.

Clev 12-19-2008 03:09 PM

Quote:

Originally Posted by wikityler (Post 79363)
I did this with my acclaim. I found that the dmm I was using, having 1/2 second measurement, wasn't responsive enough. Something a bit faster, and it would work great.

What about an analog multimeter?

NiHaoMike 12-19-2008 06:05 PM

Quote:

Originally Posted by Daox (Post 79218)
Most MAPs have voltage outputs. I'm sure some maker somewhere thought they'd be smart and put in a frequency output on something though.

And many modern multimeters also measure frequency. But if it outputs a frequency in the audible range, there's an even better way. Tap into the signal with a series resistor and capacitor and connect it to a very cheap audio amplifier. Then just listen to the tone while driving.

modmonster 12-22-2008 10:18 AM

is a MAP sensor the same as a MAF sensor? Mass Air Flow sensor? if not what would measuring a MAF tell you?

wikityler 12-22-2008 02:57 PM

Quote:

Originally Posted by modmonster (Post 79792)
is a MAP sensor the same as a MAF sensor? Mass Air Flow sensor? if not what would measuring a MAF tell you?

Map is Manifold Air Pressure. It's like an electronic vacuum gauge. MAF is Mass Air Flow, it measures the quantity of air entering the intake.

Nevyn 12-22-2008 04:11 PM

I thought it was Manifold Absolute Pressure?

Ford Man 12-22-2008 07:32 PM

Quote:

Originally Posted by Nevyn (Post 79852)
I thought it was Manifold Absolute Pressure?

Correct

modmonster 12-24-2008 03:23 PM

does voltage of MAF sensor indicate the engine load?

jazzie604 12-26-2008 06:06 PM

Quote:

Originally Posted by modmonster (Post 80205)
does voltage of MAF sensor indicate the engine load?

not really, it measures the volume of air entering the engine. this can be used as well, since the less air the engine is sucking in the less fuel it is adding to the engine. Problem is MAFs use a hertz reading which is more difficult to monitor.

modmonster 12-30-2008 03:56 PM

my BOSCH MAF gives a voltage signal 0-5v. this is calibrated to air flow rate which is directly proportional to fuel flow rate. boscheSensors (page 57)

all we need do is data log voltage and speed and we have a method of calculating MPG. or alternatively you could just display the voltage on a meter and do the mpg calculations in your head! at constant speed you know what voltage to expect, if mods reduce the voltage then you know they save fuel.

modmonster 12-30-2008 03:58 PM

can a sat nav be set up to display trip average speed?

modmonster 01-09-2009 07:58 PM

does anyone know of a portable data logger or adding machine? -let me explain

i've been thinking that if we can monitor the MAF sensor, air flow is proportional to fuel flow at 14.7:1 so we basically have a fuel flow gauge. now if we could add up these voltage values in real time (integration:)) this would give us the trip fuel used. we know mileage from the dash so we could then easily have a very basic mpg calculator.

Nevyn 01-09-2009 09:39 PM

Would I be out of line to suggest an Arduino? you could probably use it to monitor the voltage and do the math.


Or just turn it into an MPGuino......

dichotomous 01-12-2009 10:18 AM

its a very rare thing for a car to be running 14.7:1..... on accelleration it uses much more fuel, more like 12-10:1, on deccel it uses less fuel, it almost never uses 14.7:1 though.
to know your fuel, you need something to monitor the flow of fuel per mile, which likely only the computer will tell you

modmonster 01-12-2009 12:23 PM

i don't have an electronic spedometer in my car. if i just install the mpguino to the injectors will that give me any usefull fuel related information?

e.g. gallons per hour, total trip gallons ?

top_down 01-23-2009 02:24 PM

dcb, is there another analog input available on the MPGuino and enough space for some code to monitor the MAP voltage and display a live bargraph display of the engine vacuum? It might be asking too much, but I'd love to see a slightly smaller font on the MPGuino "big" displays, and a bargraph underneath showing a live vacuum reading. I hate the big ugly mechanical vacuum gauge in my Metro, but love having that additional piece of info while I'm driving.

I suppose I could do something with the appropriate parts and 10-20 LEDs, but it would be so clean to have it all on the one display.

dcb 01-23-2009 02:35 PM

A mega168 vacuum effort, done right, would need some code space. You can always gut out the code you don't like to make room (someone should start a code tweaks wiki) but given that it complicates hookup, and there is precious little code space left with the current arrangement, I doubt it would ever be "core" on the base unit.

You do want to update the bar graph as often as possible, so it looks "analog" not just once per 1/2 second, so the whole program might need redoing to do more than one thing at a time with it. There are a couple analog ports available (analog 1 and 2), might just want to build a second one for vacuum/wideband o2/???

Clev 01-23-2009 02:42 PM

dcb, do you forsee any issues using the Atmega328P? I bought the new rev MPGuino kit (I still want to order some stuff so I can socket-mount the LCD instead of soldering it, so I haven't put it together yet.) FL has the 328P-20P preprogrammed for $6.25, so I added it to the order. I wanted the room to be able to add my own project stuff later (I second the code wiki!). Do you think there will be any porting needed to run the existing code on the 328?

Daox 01-23-2009 02:44 PM

Quote:

Originally Posted by dichotomous (Post 82793)
its a very rare thing for a car to be running 14.7:1..... on accelleration it uses much more fuel, more like 12-10:1, on deccel it uses less fuel, it almost never uses 14.7:1 though.
to know your fuel, you need something to monitor the flow of fuel per mile, which likely only the computer will tell you

I totally disagree. Any modern car will likely run at 14.7:1 a good majority of the time if not more. I've monitored closed vs open loop on my matrix (which also has a wideband O2 sensor in it which I've monitored) and that sucker stays in closed loop 95%+ of the time. Only at 3000+ rpm and WOT does it break into open loop. If you back off the throttle a small amount you drop back into closed loop unless you are at very high rpms. Maybe its just a very well designed engine, but I can't believe others would be that much worse.

dcb 01-23-2009 03:01 PM

Quote:

Originally Posted by Clev (Post 84727)
dcb, do you forsee any issues using the Atmega328P?

For experimental purposes, no issues. You have to tweak your arduino installation, and I'm hoping they will cut the bootloader back down to 1k or less, but it should be pin compatible. I have not tried the 328 yet, not sure if/where mpguino is going after 1.0, or if it even needs to go anywhere, but the 328 is a distinct possibility. Gotta see how this first batch of boards goes and see where things stand after that.

Clev 01-23-2009 03:02 PM

Quote:

Originally Posted by dcb (Post 84733)
For experimental purposes, no issues. You have to tweak your arduino installation, and I'm hoping they will cut the bootloader back down to 1k or less, but it should be pin compatible. I have not tried the 328 yet, not sure if/where mpguino is going after 1.0, or if it even needs to go anywhere, but the 328 is a distinct possibility. Gotta see how this first batch of boards goes and see where things stand after that.

Cool. I'll let you know how it goes once I get it together.

cmj 09-15-2010 10:49 PM

Kinda bringing this topic back from the dead, but I thought of the exact same thing (using a MAP to gauge load) just minutes before I decided to register on this forum. I'm in super nerd mode right now (that state of mind that gets you tinkering, and nothing else gets done) so I haven't created an introduction yet.

Back on topic, I had an arduino duemilanove laying around that I was ultimately going to convert into an MPGuino, but upon further thought i'd like to get one of the mini's and run a remote display for ease of installation. Freeing up my main 'development' platform, i threw some LED's in a proto-board, hooked up some wires, installed some resistors and came up with a nice little bar graph that shows me how i'm doing engine load wise. As of now I don't have an actual vacuum gauge to determine exact kPa, or HGpI (however you choose to measure your vacuum) so I can't determine an actual scale. I've calibrated the code to what I think is the best 'load' on the motor for FE and when I punch it, the meter goes red, and when I'm idling or cruising at a good load it goes green. Spirited driving puts me in the yellow zone, so the apparatus does give me a good visual of engine load. I'll take videos of it tomorrow in the daylight. My hopes for this little project is to implement a big bar graph into the MPGuino code that allows you to set your desired optimal load and display it for you in some kind of pretty format.

gone-ot 09-16-2010 09:22 PM

...pictures and results?

cmj 09-17-2010 04:32 PM

I honestly haven't stopped tinkering with it long enough to take pics. As soon as I got the concept working with the Arduino I wanted to see if I could simplify it. Scrounging through a parts bin yielded a 555 timer, some capacitors, and some LED's. Utilizing the 555 as a bistable circuit allowed me to light a green LED under a specified load/current, and a yellow LED over the same threshold. I liked how simple and small the setup was and there was very little noise due to a later added capacitor.

Today as I was driving the 70 miles up to Ball State University to see my lady friend on her birthday I was tickled that the gauge was so simple and effective, but as soon as I picked out a semi to draft up I69 with, I got to thinking about how I could accurately gauge the effectiveness of the draft. When I get home Sunday, I'm going back to the arduino and a nice LED screen to show MAP % as well as TPS % so I can gauge how effective at saving fuel my current driving is. Once again when I get around to buying another duino, and putting an MPGuino setup together, I would like to implement this setup as a screen.

I will make a thread with my findings and some MAP and TPS scales when everything is concrete. It's just hard for me to believe noone else has went down this path as well. FE is greatly dependent on engine load. Some say aerodynamics is key, but a smoother airflow doesn't get you more MPG, it's taking LOAD off of your vehicle that does. A lot of cars come with the sensors already in place to show you how you are driving, I'm just trying to use them to my advantage!

gone-ot 09-17-2010 07:06 PM

...we inveterate tinkerers are...well...inveterate at tinkering!

dcb 09-17-2010 07:37 PM

OP is on a very productive path though, I wouldn't abandon the atmega platform for 555s though, the atmega will make a lot more interesting optons (software logic and lots of inputs/outputs).

I did however do some rough "calibrations" with an arduino and a map sensor and a brake bleeder here for a starting point http://ecomodder.com/forum/showthrea...nsor-5208.html

cmj 09-17-2010 09:43 PM

I don't know if you are referring to me as the OP but I'm not abandoning the atmega platform, I just look for ways to cut down on "moving parts" I'm moving back to the dev board. I can't wait to get home on Sunday to play with this. My wideband setup that was on the race car had a 5v o2 output for tricking stock ECU's into thinking there was a narrowband sensor in line. Once I get the MAP and TPS sensors sorted, I think i'm gonna look at adding that to the board. The whole thing could possibly end up being an add on unit to the MPGuino, because as it looks this is going to take up some space that the MPGuino doesn't have.

dcb 09-17-2010 11:05 PM

The other thing about these microcontrollers is that it can replace hundreds of "logic" ICs and discrete components and can really reduces the parts count dramatically, for reduced hardware costs. I don't see any real benefit to hardwiring the logic in chips when it can be in firmware, for this sort of application anyway.

Parts count is
atmega 328 (perhaps put the lilypad bootloader on it if you don't want to use a crystal or sort out the nitty gritty)
5v regulator
electrolytic capacitor
handful of leds and resistors

and thats it, for a relatively simple led display of vacuum.


FYI, the guino does have available 3 available adc ports and some coding room with a 328. Hardware wise it is trivial to hook up the map signal (or tps), you just hook it up to an available analog port, problem is getting over the software development hump.

bobski 09-18-2010 02:21 AM

Would it be possible to include the I2C library and free up the requisite pins if they're being used? It would make hookup to any number of remote devices (such as an SAA1064-based bar graph or numerical display) a four wire affair... Two for power/ground, two for data.

dcb 09-18-2010 07:50 AM

SAA1064 is an interesting looking chip, yah certainly it is possible. $2.50 chip that you can control 32 LEDs with a 2 wire interface has it's applications. I don't like that i2c uses 2 analog pins though. But for the "simple" 7/8 bar Vacuum gauge it is not necessary since the chip can handle that load and has the pins to spare in a standalone unit.

You could also implement a standalone gauge bar graph with a couple LM339,s that is what is used for my cheap electric scooters "dashboard", to indicate battery voltage and throttle, but the atmega is still one chip and is hardly expensive and is infinitely more flexible. Of course there are tons of other microcontroller chips out there too, but arduino is a good starting point.

bobski 09-18-2010 01:16 PM

Yeah, analog pins are in short supply, but I2C uses device addresses so you can put many devices on the same two pins.
There are some inexpensive I2C general-purpose IO expander chips out there as well, so maybe the buttons (which monopolize 3 analog pins) could be offloaded to one of those? Many such chips provide an interrupt output that goes true when an input changes, and stays true until the chip state is read. Maybe that could be fed to one of the MPGuino's interrupt pins, rather than the injector pulsewidth measurement using them both? Anyone know why that was done?


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