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-   -   VSS problem (https://ecomodder.com/forum/showthread.php/vss-problem-33946.html)

mirkwood 06-12-2016 08:39 AM

VSS problem
 
Hi

This is not the first time i try to solve this.. had given up, but now saw the MPGuino in the drawer again..

In my first car, a Alfa romeo 155 it worked flawless. Now in my Alfa romeo 75 I cant get a good VSS signal?.

Up until 20-40km/h MPGuino actually shows the speed, but then goes the oppesit way down to Zero beyond that speed??.

----

This is from the lead going directly into the MPGuino, .. I actually have no clue how to operate this handheld device, kinda blindly push buttons.. just, i can see that there actually is a signal, and that i had to put it at "5v" to get it to best fit the screen.

http://ac1rqq.dm2302.livefilestore.c...612_140740.jpg

Any ideas?. I have seen many schematics of ways to alter the signal and etc.. But is that something I should try?.
Is the signal too strong?.


A little info: The Transducer speed sensor sits in the gearbox (gearbox in rear of car), and goes to a little box under the backseat, pulse generator/amplifier and then to the speedometer itself.

Update: Have tried to run a shielded cable directly from the pulse generator to the MPGuino, same happens.
And run test procedures on the pulse generator and transducer, all seemingly ok.

Actually the signal seems up to 12v strong in pulses.

t vago 06-12-2016 03:43 PM

It sounds like the MPGuino is being fed a VSS signal that is too fast for it to handle.

Can you tell me what vehicle speed that above o'scope output represents?

mirkwood 06-12-2016 06:11 PM

Quote:

Originally Posted by t vago (Post 516254)
It sounds like the MPGuino is being fed a VSS signal that is too fast for it to handle.

Can you tell me what vehicle speed that above o'scope output represents?

Thanks for reply :)
Around 50-60km/h /// 31-37mp/h I believe i did at that momment.

Yeah, otherwise why would it seem fine and then drop?.
But then.. wouldn't my car be strange different than others?, if it makes a signal so fast that the MPGuino can't follow?.

I have been thinking that i could try and tap into the signal before the signal generator/amplifier, if that would make a difference.


Any suggestions for oscilloscope settings and what i should then be seeing are welcome too.

t vago 06-13-2016 12:00 AM

Quote:

Originally Posted by mirkwood (Post 516263)
Thanks for reply :)
Around 50-60km/h /// 31-37mp/h I believe i did at that momment.

Glad to help. :-)

If this is so, then it would appear that your Alfa is set up to deliver around 18000 pulses per mile, or about 11200 pulses per kilometer. I have not performed a definitive analysis of the upper limit of what the MPGuino can handle, but it seems that you may have found its upper VSS limit, given its parameter settings.

Quote:

Originally Posted by mirkwood (Post 516263)
Yeah, otherwise why would it seem fine and then drop?.

This has a lot to do with digital signal theory. Specifically, your Alfa might have made a VSS signal for the MPGuino, that is higher than what is known as the Nyquist frequency. That is defined as the frequency at which something can be digitally sampled without introducing errors. That is typically 1/2 the sampling frequency.

From what you have described, it appears that the MPGuino, as programmed with default parameters, cannot sample VSS signals that are more than about 187 Hz. That would be the Nyquist frequency for the MPGuino, which means that the MPGuino sampling frequency is about 374 Hz.

What you're seeing is this:

Once your Alfa's VSS goes above 187 Hz, the MPGuino will effectively see a frequency of (374 - VSS) Hz, and that will cause your indicated speed to fall at speeds above 60 kph. At around 120 kph, you'll probably see a speed of 0.

With most cars, they will never see this problem as their VSS signals would not go much above 10000 pulses per mile. However, I am thinking that your Alfa has a VSS that is... 18000 pulses per mile? Is that right?

Quote:

Originally Posted by mirkwood (Post 516263)
But then.. wouldn't my car be strange different than others?, if it makes a signal so fast that the MPGuino can't follow?.

I have been thinking that i could try and tap into the signal before the signal generator/amplifier, if that would make a difference.


Any suggestions for oscilloscope settings and what i should then be seeing are welcome too.

I think you will just need to adjust a parameter in the MPGuino itself.

There is something called "VSS Debounce" and it is set to a program default of 2. This is for purely mechanical vehicle speed sensors that use a reed switch to generate a VSS signal.

As your Alfa uses an electronically generated VSS signal, you can safely set "VSS Debounce" to zero. Do this, and tell me if your problem goes away.

mirkwood 06-13-2016 04:26 AM

Quote:

Originally Posted by t vago (Post 516269)
Glad to help. :-)

If this is so, then it would appear that your Alfa is set up to deliver around 18000 pulses per mile, or about 11200 pulses per kilometer. I have not performed a definitive analysis of the upper limit of what the MPGuino can handle, but it seems that you may have found its upper VSS limit, given its parameter settings.



This has a lot to do with digital signal theory. Specifically, your Alfa might have made a VSS signal for the MPGuino, that is higher than what is known as the Nyquist frequency. That is defined as the frequency at which something can be digitally sampled without introducing errors. That is typically 1/2 the sampling frequency.

From what you have described, it appears that the MPGuino, as programmed with default parameters, cannot sample VSS signals that are more than about 187 Hz. That would be the Nyquist frequency for the MPGuino, which means that the MPGuino sampling frequency is about 374 Hz.

What you're seeing is this:

Once your Alfa's VSS goes above 187 Hz, the MPGuino will effectively see a frequency of (374 - VSS) Hz, and that will cause your indicated speed to fall at speeds above 60 kph. At around 120 kph, you'll probably see a speed of 0.

With most cars, they will never see this problem as their VSS signals would not go much above 10000 pulses per mile. However, I am thinking that your Alfa has a VSS that is... 18000 pulses per mile? Is that right?



I think you will just need to adjust a parameter in the MPGuino itself.

There is something called "VSS Debounce" and it is set to a program default of 2. This is for purely mechanical vehicle speed sensors that use a reed switch to generate a VSS signal.

As your Alfa uses an electronically generated VSS signal, you can safely set "VSS Debounce" to zero. Do this, and tell me if your problem goes away.

I don't know if it is 18000 pulses per mile (mine also in km i think) .. hmm.. can't read the scope so well, and car technical manual doesn't state.
Someone has made a fine diagram of the signal amplifier if that would be a help to help.
EDIT did you mean what i use in the settings?, got it set at 26280 VSS, it is where it seems ok correct for low speeds.
MPGuino indicates zero speed at exactly 55km/h~ 34mp/h


Is "VSS Debounce" the same as VSS delay?, cause i don't recall seeing "VSS Debounce" in settings. Have tried both setting that to 2..1.. and Zero, and still the same.

t vago 06-13-2016 09:44 AM

Quote:

Originally Posted by mirkwood (Post 516277)
I don't know if it is 18000 pulses per mile (mine also in km i think) .. hmm.. can't read the scope so well, and car technical manual doesn't state.
Someone has made a fine diagram of the signal amplifier if that would be a help to help.
EDIT did you mean what i use in the settings?, got it set at 26280 VSS, it is where it seems ok correct for low speeds.
MPGuino indicates zero speed at exactly 55km/h~ 34mp/h

26280 is really, really high. You will want to place a frequency divider between your VSS signal output and the MPGuino.

Something like this:

http://1.bp.blogspot.com/-C0HaJ6bS1i...IA/s1600/4.png

Quote:

Originally Posted by mirkwood (Post 516277)
Is "VSS Debounce" the same as VSS delay?, cause i don't recall seeing "VSS Debounce" in settings. Have tried both setting that to 2..1.. and Zero, and still the same.

Yah, they're the same. I was going off an early MPGuino code version. What version of MPGuino code do you have?

mirkwood 06-13-2016 12:35 PM

Quote:

Originally Posted by t vago (Post 516292)
26280 is really, really high. You will want to place a frequency divider between your VSS signal output and the MPGuino.

Something like this:

http://1.bp.blogspot.com/-C0HaJ6bS1i...IA/s1600/4.png



Yah, they're the same. I was going off an early MPGuino code version. What version of MPGuino code do you have?


Hehe :D yeah okay, really really high. :( :)

Yeah, I just noticed this guy had similar problem http://ecomodder.com/forum/showthrea...mit-29787.html
and he was to do a divider aswell, but no conclusion.

Hmm... is this something that can be bought somewhere pre-built?, I tried to do a search, but either i am not using the right words, or then it is rare.

If i am to solder myself then i need a really detailed plan. Soldering no problem, but schematics not my strongest side.

In another thread on a Alfa romeo site i found this, but it is an more expensive option.
Universal Speedometer Signal Interface


Where do i see the code version?, on the unit itself?.

Thanks again :).

t vago 06-13-2016 11:28 PM

Quote:

Originally Posted by mirkwood (Post 516300)
Hehe :D yeah okay, really really high. :( :)

Yeah, I just noticed this guy had similar problem http://ecomodder.com/forum/showthrea...mit-29787.html
and he was to do a divider aswell, but no conclusion.

Hmm... is this something that can be bought somewhere pre-built?, I tried to do a search, but either i am not using the right words, or then it is rare.

If i am to solder myself then i need a really detailed plan. Soldering no problem, but schematics not my strongest side.

You could get yourself a 4013 dual D flip-flop CMOS chip. It's a fairly basic piece of 1970s technology that should cost around $0.50 per chip. It will accept a car battery or alternator voltage with no problem.

Here's a datasheet for one -> https://www.fairchildsemi.com/datash...D/CD4013BC.pdf

Get a 14-pin DIP chip, a 14-pin DIP socket for the chip, a 0.1 uf capacitor (preferably not electrolytic), and solder jumper wires as described in the below pin assignments:

10 <-> 8 <-> 7 <-> 6 <-> 4

3 -> 2.2 kohm resistor -> 14
3 -> input Alfa VSS signal
1 -> 11
14 -> V+ (same source wire that powers the MPGuino, for instance)
7 -> ground
14 -> 0.1 uf capacitor -> 7
1 -> 11
13 -> VSS output to MPGuino
2 -> 5
12 -> 9

Quote:

Originally Posted by mirkwood (Post 516300)
In another thread on a Alfa romeo site i found this, but it is an more expensive option.
Universal Speedometer Signal Interface


Where do i see the code version?, on the unit itself?.

Thanks again :).

No problem.

The MPGuino version can be found on the screen, for approximately 2 seconds after it is first powered up.

mirkwood 06-14-2016 07:56 AM

Quote:

Originally Posted by t vago (Post 516326)
You could get yourself a 4013 dual D flip-flop CMOS chip. It's a fairly basic piece of 1970s technology that should cost around $0.50 per chip. It will accept a car battery or alternator voltage with no problem.

Here's a datasheet for one -> https://www.fairchildsemi.com/datash...D/CD4013BC.pdf

Get a 14-pin DIP chip, a 14-pin DIP socket for the chip, a 0.1 uf capacitor (preferably not electrolytic), and solder jumper wires as described in the below pin assignments:

10 <-> 8 <-> 7 <-> 6 <-> 4

3 -> 2.2 kohm resistor -> 14
3 -> input Alfa VSS signal
1 -> 11
14 -> V+ (same source wire that powers the MPGuino, for instance)
7 -> ground
14 -> 0.1 uf capacitor -> 7
1 -> 11
13 -> VSS output to MPGuino
2 -> 5
12 -> 9



No problem.

The MPGuino version can be found on the screen, for approximately 2 seconds after it is first powered up.


Does this look correct?.

One question, i know the capacitor has a negative side, clearly marked.. but the resistor, to where does the golden strip point?.

http://ac1rqq.dm2302.livefilestore.c.../alfa75VSS.jpg


Hmm.. didn't show code version on startup for some reason, tried twice.

t vago 06-14-2016 01:04 PM

Quote:

Originally Posted by mirkwood (Post 516338)
Does this look correct?.

One question, i know the capacitor has a negative side, clearly marked.. but the resistor, to where does the golden strip point?.

The resistor golden strip can point to either pin - it does not matter with resistors.

Quote:

Originally Posted by mirkwood (Post 516338)

This drawing looks correct. It should solve your problem.

Quote:

Originally Posted by mirkwood (Post 516338)
Hmm.. didn't show code version on startup for some reason, tried twice.

That's a little strange, but as long as your MPGuino works otherwise, it doesn't matter.

mirkwood 06-14-2016 02:17 PM

Quote:

Originally Posted by t vago (Post 516367)
The resistor golden strip can point to either pin - it does not matter with resistors.



This drawing looks correct. It should solve your problem.



That's a little strange, but as long as your MPGuino works otherwise, it doesn't matter.

Ah okay :), thought i was told once that it mattered, maybe that is diodes instead.

Awesome, should be no problem building and installing, already ordered the parts. Signal would be divided by 4, right?

Sometimes i have wondered if mine is some "fake" cheapo copy. But i got it from here, also well known maker i think. But maybe not the official-official MPGuino trip computer - MPGuino



-------
Hopefully soon i will have happy conclusion to thread :D, miss having the MPGuino.

And the neat little panel I made can finally replace the ashtray as i intended.

(From 2-3 years ago)
http://lfpjkw.dm2302.livefilestore.c...A/IMG_6101.jpg

http://lfpjkw.dm2302.livefilestore.c...Q/IMG_6106.jpg

http://lfpjkw.dm2302.livefilestore.c...g/IMG_6603.jpg

mirkwood 06-16-2016 02:25 PM

Quote:

Originally Posted by t vago (Post 516326)
You could get yourself a 4013 dual D flip-flop CMOS chip. It's a fairly basic piece of 1970s technology

Thanks again, it works now! :D, finally solved.

The soldering was a bit more tricky than I thought it would be, so tiny, and points so close, but it seems to work at exactly 6500 VSS now, tho still needs some calibration.

:thumbup:


Here are the results, I think both times i drove 40km/h.

http://ac1rqq.dm2302.livefilestore.c...r-MI5Y/mpg.jpg

ECONORAM 01-03-2017 10:34 PM

Quote:

Originally Posted by mirkwood (Post 516245)
Hi

This is not the first time i try to solve this.. had given up, but now saw the MPGuino in the drawer again..

In my first car, a Alfa romeo 155 it worked flawless. Now in my Alfa romeo 75 I cant get a good VSS signal?.

Up until 20-40km/h MPGuino actually shows the speed, but then goes the oppesit way down to Zero beyond that speed??.

I had this problem with my home built VSS. I have a corroplast disc clamped to my driveshaft, with an LED and an IR photosensor reading light pulses through slots in the disc. However, with 4 slots in the disc my MPGuino would do what you described, starting at 35 mph. I covered 2 slots and it worked until 75mph. I only run one slot now, as some highways have an 85mph speed limit. :) Just need to get a reliable IR sensor installed...

[edit] nice looking panel enclosure!

t vago 01-04-2017 09:41 AM

I made some more modifications to my version of the MPGuino code, and it now easily handles higher frequency VSS signals. An Ecomodder in London is using his ABS wheel speed sensor for his VSS, his pulses per mile setting is near 100000, and he reports no problems with the VSS readings.

ECONORAM 02-18-2017 01:21 PM

So, as an end user of an MPGuino, am I able to load your updated code myself tvago, or do I need some sort of gizmo to help me do that? Or do I just buy a new preloaded chip? Mine is a meelis version...
[edit] will your new code read signals from the ABS or something like the Dodge output speed sensor? The OSS has about 33,000 counts/mile. I couldn't get that to work with my first MPGuino. Don't know if that's because it was a 5v signal, or because it was above the VSS limit...

t vago 02-22-2017 01:23 PM

Quote:

Originally Posted by ECONORAM (Post 534622)
So, as an end user of an MPGuino, am I able to load your updated code myself tvago, or do I need some sort of gizmo to help me do that? Or do I just buy a new preloaded chip? Mine is a meelis version...
[edit] will your new code read signals from the ABS or something like the Dodge output speed sensor? The OSS has about 33,000 counts/mile. I couldn't get that to work with my first MPGuino. Don't know if that's because it was a 5v signal, or because it was above the VSS limit...

The original MPGuino code appears to have a upper speed limit that is due to the amount of time required to transfer all of the raw speed/injector data from the raw measurement trip variable to the instant trip variable. While small, this amount of time was large enough to interfere with intercepting VSS pulses as they occurred. My code bypasses that rather easily. There's a member in London (whom I haven't heard back from in a while, though) who is using his ABS speed sensor with MPGuino, with something like 100K pulses/mile, and he's reported that my code works well for him.

My code should read from your ABS speed sensor. I am going to install an MPGuino into both my Dakota and my Durango, later on this year, to replace the overhead trip computer that I never really liked all that much. I was considering using the VSS output signal from the ABS CAB module, but reading directly off the output speed sensor, on the rear end, might be more accurate.

As for your inquiry? I could send you a replacement chip with my code programmed into it. PM me if you're interested.


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