Newbie with Question - Manifold Absolute Pressure Voltage
Suzuki Phil
Posts: 10
Hello All,
I'm a motorhead who's gone and turbo'd his car. What I've done is removed the stock MAF (mass airflow sensor) and replaced with a MAP (manifold absolute pressure) sensor. All this is controlled by a piggy back tuning computer wired to my stock ECM. I access the piggy back via a laptop and program the engine with it.
Here is the problem. The MAP sensor has twitchy voltage, meaning it's constantly varying (at idle or cruise) from a calculated average voltage. Can I use a Basic Stamp to read this voltage and set a zone that it cannot exceed from the average? Remember the voltage is changing to due various conditions, load, boost, throttle position etc. I want to reduce the amount of variation in the signal itself. Some electronic guys I've talked to say to add a capacitor but I don't think this will solve my problem.
This variation causes an erratic idle and cruise conditions, my stock ECM was not programmed to use the MAP.
The MAP sensors outputs a dc voltage from .1v to 5v max at full boost.
Thanks,
Philip
Post Edited (Suzuki Phil) : 3/9/2005 2:33:43 AM GMT
I'm a motorhead who's gone and turbo'd his car. What I've done is removed the stock MAF (mass airflow sensor) and replaced with a MAP (manifold absolute pressure) sensor. All this is controlled by a piggy back tuning computer wired to my stock ECM. I access the piggy back via a laptop and program the engine with it.
Here is the problem. The MAP sensor has twitchy voltage, meaning it's constantly varying (at idle or cruise) from a calculated average voltage. Can I use a Basic Stamp to read this voltage and set a zone that it cannot exceed from the average? Remember the voltage is changing to due various conditions, load, boost, throttle position etc. I want to reduce the amount of variation in the signal itself. Some electronic guys I've talked to say to add a capacitor but I don't think this will solve my problem.
This variation causes an erratic idle and cruise conditions, my stock ECM was not programmed to use the MAP.
The MAP sensors outputs a dc voltage from .1v to 5v max at full boost.
Thanks,
Philip
Post Edited (Suzuki Phil) : 3/9/2005 2:33:43 AM GMT
Comments
The number of samples to use depends on the frequency of your noise and your sampling frequency. The tradeoff of the number of samples used is: too few and the noise isn't as filtered, too many and you reduce the responsiveness of the circuit.
One means of compromise if you find the requisite number of samples to filter out the noise make the system too sluggish in response to large changes is to do what you sortof hit on, if the difference of the current sample and the previous sample exceeds a threshold, just use the current sample (don't forget to readjust the previous sample if you stored it in its shifted value before comparing it to the current sample. Also continue to fill the previous sample buffer during this mode, or you will get a ringing output from the old values in the buffer when you return to using the moving average filter). This mixed mode is where a stamp is superior to a capacitor (which acts like a moving average filter).
Hope this helps,
Paul
Post Edited (Paul Baker) : 3/9/2005 5:32:11 AM GMT
Post Edited (Paul Baker) : 3/9/2005 2:35:17 PM GMT
Thanks,
Philip
A BS2 is unlikely fast enough, the BS2SX or BS2P may do the job.
Is 'smoothing' the map sensor signal the only thing you want to do with the stamp?
If so, take a look at the SX, and there is a new compiler from Parallax making the SX easy to use, and there is no question about the SX being fast enought to do the job.
The SX is about $45 cheaper than a BS2
If you're using the 'sliding' average filter, then you can assume that, if you're sampling 10x per second but the readings are 20x per second, then you can get guess inbetween the ones you miss!· So, if the stamp sampled one reading at 100 and the next at 110, you could 'assume' the one missed in between was 105....yes/no?!?!
If you're averaging, you might want to start with a "profile" that gets updated as you start.
So, determine that ok, when I first start my car, the engine is cold and idle is high....so use this setting.· Then have it monitor as things warm up and settle.· Then go in to your actual 'on-the-fly' tuning.
If you have a laptop connected and you are debug or serial'ing data out, you'll bog the stamp down too much to be of use!
So keeping your code streamlined is what you want.
If you have the stamp....then you're not out any $ and I'd say give it a try!· If you don't have a stamp....get one, if it doesn't work, they're great for lots of other fun things! lol· Certainly if you're new to Parallax's products, the Basic Stamp modules are fairly easy to program with their editor software....
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Philip
Post Edited (Suzuki Phil) : 3/9/2005 5:12:01 PM GMT
Post Edited (Paul Baker) : 3/9/2005 5:16:06 PM GMT
Philip
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There are "access" times....basically, in PBASIC, when you put in a Pulsin or a serout command, that gets translated in to a Smile load of code and on the stamp it has to retrieve some items from it's EPROm...someone will word all this properly for me....but the jist is that it takes time to run commands/functions.·
You could easily get 20/sec I'm sure.....not sure about 120/sec
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
I appreciate the help and we'll see how it works out. I've been wanting to buy a Basic Stamp anyway to play with [noparse]:)[/noparse]
Philip
Ken
He needs to send the signals to his 'tuning piggyback computer'....he can read the sensor whenever he can....but could he get away with constantly sending out the last read sensor reading.
Could he fool the computer by sending 'last-read' data until he has a chance to read it again?!· With a timeout of course (in case things go wrong).
This would create lag....but at 100x/sec or whatever, how obvious would it be?!
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
I want to solve the voltage variation problem first then I'll tackle the reaction issue if it still exists. I purchased the SX lite kit today not the BS2SX kit.
I've already confirmed the variation issue by using a precision dc power supply connected to the analog input of the piggy back which feeds the ECM. Setting the voltage at .75v (idle voltage for MAP sensor) with no variation produces a nice smooth idle and a steady wideband O2 reading.
Philip
Do you offer programming services?
Philip
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heres the link to the code: http://www.atmel.com/dyn/resources/prod_documents/avr222.zip
If you need to know what an assembly command is, heres their doc on the instruction set: http://www.atmel.com/dyn/resources/prod_documents/DOC0856.PDF
You'll note there is alot more commands in the AVR architecture than the SX, but don't worry there is always a means for writing code for the SX that achieves the same thing, and the speed of the SX results in faster code execution even though it on ocassion needs to execute more commands to achieve the same thing.
Philip