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Old 06-13-2008, 11:52 PM   #281 (permalink)
dcb
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P.S. getting tired of the speculation about what is going to happen to the chip (or peoples cars or their paypal accounts) so I put the donations towards a used oscilloscope.

Edit: also this did not start out as a finished product suitable for permanent installation or for production, it was intended to be a simple to assemble and inexpensive DIY MPG gauge that would be useable ASAP, which would undergo several software upgrades during its lifetime so that the nice folks actually doing the software would not be overburdened by deliverables and deadlines. My wife is already using hers to good effect, and is bugging me for the large number font thing

Edit: She is running the very first mpguino pictured in post 1, has been for weeks now.

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Old 06-14-2008, 10:27 AM   #282 (permalink)
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it was intended to be a simple to assemble and inexpensive DIY MPG gauge that would be useable ASAP, which would undergo several software upgrades during its lifetime so that the nice folks actually doing the software would not be overburdened by deliverables and deadlines.
I apologize for saying anything in the first place, it was not my intention to piss you off. I will keep my mouth shut from now on.
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Old 06-14-2008, 10:50 AM   #283 (permalink)
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Forgive me if I sound pissed, it is hard for folks to appreciate the effert involved, and for folks to jump in and talk about paypal refunds, specious associations to hardware failures, or worse yet, car fires, is destructive talk. It is simple though, if you want to make your point I need real bench test results and real reseach and figures, not emotional arguments and speculation and invalid assumptions about the target audience. I.E. you might have to do some work to make your point cuz talk is cheap.
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Old 06-14-2008, 11:22 AM   #284 (permalink)
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Found a site showing injector specifications.
http://www.caspeed.com/multec-injectors.html

One of them is...
STATIC FLOW RATE = 2.44 gr/sec
DYNAMIC FLOW RATE = 0.487 gr/sec
where DYNAMIC FLOW RATE means FLOW AT 2.5mS PULSE WIDTH AND 10.0mS REPETITION RATE. The DYNAMIC test is the 25% duty cycle, therefore we should see one fourth of STATIC data if there were no mechanical delay.

However, the DYNAMIC one is one fifth of the STATIC.
DYNAMIC = STATIC * ( 2.5mS - X ) / 10mS
0.487 = 2.44 * ( 2.5 - X ) / 10
X = 0.5mS
This injector has 0.5mS mechanical delay.

Yoshi
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Old 06-14-2008, 12:09 PM   #285 (permalink)
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folks to jump in and talk about paypal refunds, specious associations to hardware failures, or worse yet, car fires, is destructive talk.
dcb,
I do appreciate the effort involved, and I am in awe of what you have created.
I had always assumed your final plan was to package and sell this item yourself.
As a final product that anyone could just "put in".
I regret my error.
My comments were based on the "dcb is going to sell a product" assumptions.
The paypal I was worried about was thus YOUR paypal.
I am not expecting for you to solve these issues (if they are even real) for ME.
I plan to use optoisolators.
I was just doing what I do at work when there is a new design that is going to be a product for sale.
I never said I though there would be a car fire. I do not think that possible.
Sincerely,
ttoyoda.
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Old 06-14-2008, 03:55 PM   #286 (permalink)
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Quote:
Originally Posted by Yoshi View Post
Found a site showing injector specifications.
http://www.caspeed.com/multec-injectors.html
Nice! My wife was kind enough to crunch the numbers for all those, here are some stats:

min .50
max .81
mean 0.666
std deviation 0.086

If anyone has similiar stats for other injectors and knows which injectors are used on what cars we can try and account for it in the setup at some point. I'll call it .5 for now in the code.
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Old 06-14-2008, 04:28 PM   #287 (permalink)
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Quote:
Originally Posted by Yoshi View Post
Found a site showing injector specifications.
http://www.caspeed.com/multec-injectors.html
Thank you for posting that helpful table. I should have known better than to doubt you (when I suggested that no correction factor is needed). The table you posted has convinced me that there is indeed a need for a correction factor. However, I am going to risk repeating my mistake, by doubting you again, but this time in the other direction.

Quote:
DYNAMIC = STATIC * ( 2.5mS - X ) / 10mS
0.487 = 2.44 * ( 2.5 - X ) / 10
X = 0.5mS
This injector has 0.5mS mechanical delay.
Your equation is correct. And when you apply it to the first injector on the list, it does show that the proper correction factor is 0.504mS. Trouble is, the other injectors on that table seem to behave differently. When you apply your equation to the other injectors, they all have correction factors higher than that. The other correction factors range from 0.550mS to as high as 0.805mS. That latter number applies to the last injector at the bottom of the second table.

(I guess I was doing this at the same time dcb's wife was. And it's nice to see that we found the same maximum!)

And it turns out that using 0.500mS instead of 0.805mS (for that particular injector) will lead to an overall error of almost 18%. The error is large because the absolute difference between those two numbers represents a large portion of the pulse width (2.500mS).

I also looked at other injector specs (like here: http://www.racetronix.com/), and they support my finding, that the discrepancy between static and dynamic flow cannot be handled by a single, universal correction factor.

I think this is ultimately a very manageable problem, because there are various ways an end-user could determine the proper correction factor to apply for his vehicle. But I think it's probably a good idea to make this a parameter that can somehow be altered by the user.
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Old 06-14-2008, 04:29 PM   #288 (permalink)
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Quote:
Originally Posted by Yoshi View Post
However, I set it 0.5msec and took a lot of fuel consumption data on a city and highway driving
I hope you don't mind if I ask you something about this. Fuel-use calibration seems like a very troublesome problem, because it seems to me that we are relying on the pump nozzle to shut off in a reliable, consistent manner. I have a feeling this can produce large errors, especially when buying a small amount of fuel. On the other hand, the errors will tend to equalize, over time.

Anyway, I wonder what technique you have been using in this regard, as far as how you gather your fuel consumption data. You might have some tips that could be valuable for others to hear.
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Old 06-14-2008, 04:30 PM   #289 (permalink)
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Quote:
Originally Posted by dcb View Post
a used oscilloscope
You probably realize that you can also look at the injector waveform if you send it to your PC through the audio input. You also probably realize there are various PC-based scopes that use a special hardware interface to bring in data via a serial port. But I'm not enough of a scope user to know why someone might prefer a 'real' scope.

Quote:
this did not start out as a finished product suitable for permanent installation or for production, it was intended to be a simple to assemble and inexpensive DIY MPG gauge that would be useable ASAP
I just want to offer my perspective as someone who has a lot of experience in some very professional software development organizations. You're doing a superb job of resisting feature-creep, and keeping focus on the original design statement. In other words, you're avoiding some of the most common reasons that projects fail. This takes a lot of discipline.
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Old 06-14-2008, 04:30 PM   #290 (permalink)
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Originally Posted by ttoyoda View Post
Both these methods *might* be valid if you do them on a long, dead straight road that is dead flat. Any turns or any hills up or down are going mess up the results, because you have traveled more surface miles than the "as the crow flies" miles that google/gps are showing.
You're raising two issues, curves and elevation. First let's talk about elevation.

It's true that perfectly flat roads are hard to find, but I think you're greatly overestimating the magnitude of the problem. On interstate highways, for example, I think the maximum grade is typically 6%. The average grade on the Pike's Peak race is 7%. A 6% grade would introduce a distance error of only 0.18% (derived via simple triangle math). To get an error of more than 1%, you'd need a 15% grade (or steeper). That's pretty steep. Even if you live in a hilly area, I think it should be easy to find at least a few reasonably-long road segments that don't contain any grades of nearly that magnitude.

The steepest hills in San Francisco are at a grade of about 32%. That would still introduce an error of less than 5%.

Aside from all that, Google Earth provides detailed elevation data. That means it's easy to be aware of the grade, and adjust for it. For example, I can use GE to determine that my driveway is 95 feet long, with an elevation change of 5 feet. So that's about a 5% grade.

Another tool for measuring grades and elevations is here: http://www.toporoute.com/. This tool seems to get data from maps.google. I have a feeling this is basically the same data in GE, but it's a different approach to getting at it.

OK, enough about elevation. Let's talk about curves. The GE Ruler feature has two settings, Line and Path. If you use Path, you can essentially draw curves, and therefore measure the length of a curved road. Of course the job is easier if the road is relatively straight. But it doesn't need to be perfectly straight, and it certainly doesn't need to be perfectly straight over a long distance.

Quote:
The google earth ruler feature may offer a lot of digits, but I would suggest that there is no way it is good to 1/100 of an inch.
I didn't mean to suggest that it's practical to use GE to make accurate measurements down to 1/100 of an inch. Even though it reports results with that level of precision. However, for our purpose, we don't need accuracy down to 1/100 of an inch. We just need a few feet, and GE can definitely do that. For example, it has no trouble telling me that the fire hydrant in front of my house is 22 feet from my driveway. Or that the skylights on my roof are 10 feet apart. I know that these results are correct, within a few inches. If instead of using landmarks 10 feet apart, I use landmarks a mile apart (and GE obviously lets me do that), then I can measure a mile with an accuracy of a few inches. This is very competitive with any other method I know of.

Quote:
You cannot even resolve where the sloped edge of a curb, or the edge of a road starts from those views.
It could be that this varies depending on what part of the world you're looking at. If you look at Times Square, for example, you can zoom in so your eye altitude is about 200 feet, and then it's pretty easy to find out that 45th St is about 33 feet wide, curb-to-curb. Do I have this answer to 1/100th of an inch? Of course not. But I don't need that.

So for the roads I'm looking at, GE definitely lets you clearly see where the curb ends and the road begins. But it could be that for certain areas, GE is using photos with lower resolution, and you might be looking at one of those areas.

For comparison, let's consider the traditional approach to measuring distance: your odometer. We all know that changing tire size will introduce an error. But what about tire wear? If you do some calculations, you realize that worn tires will produce an error of about 1% in your odometer reading. In other words, the error introduced by normal tire wear can very easily exceed the error introduced by using GE and not bothering to account for grades. And it's easy to account for grades and therefore eliminate even that small error.

Quote:
What is the accuracy of GPS now, +/- 30 feet?
Civilian GPS is accurate to about 50 feet. So you're right, GPS is probably not the best way to do a VSS distance calibration. But it's still probably better than the traditional method: your odometer. Unless you have a better idea, but you haven't mentioned what it is.

To summarize, these are the most obvious methods I know about, to calibrate automotive distance, in descending order of what I think the accuracy is:

A) Google Earth
B) Mile markers placed by your highway department (as mentioned by diesel john)
C) GPS
D) your odometer

Regarding D, it should be noted that they are not famous for being accurate, even before you start worrying about things like tire size and wear.

dcb, sorry for the tangent. I know you want to keep this thread focused on development issues, but this seems at least somewhat relevant. Hopefully.


Last edited by monroe74; 06-14-2008 at 04:43 PM..
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