MPGuino release one workspace

[MilesPerTank]

Well the Zener is reverse biased.

The zener I used isnt getting enough current to stabilize at 5V.

[dcb]

Why do we care if the zener stabilizes? Is it causing greater than 5v spikes on the atmega (can you scope on the chip?) Would a smaller resistor better protect the chip? And why do you think the zener is reverse biased during the inductive spike?

[dcb]

We really need an oscilloscope on the IO pins in an actual car is what we need.

[MilesPerTank]

Originally Posted by dcb

Why do we care if the zener stabilizes? Is it causing greater than 5v spikes on the atmega (can you scope on the chip?) Would a smaller resistor better protect the chip? And why do you think the zener is reverse biased during the inductive spike?

Well the concern would be solely its high being near the slicer threshold of a 1 versus 0.

Zener diodes are reverse biased by design to operate in the "zener" breakdown region.

Data Point 1992 honda civic cx
#define vssPulsesPerMile 4100ul

MPH was within 2-3 of the gauge cluster. More fine tuning could be done to match them exactly. I'm not running OEM tires so I will probably do that calibration with a GPS unit. I thought of a neat feature to add to the program : basically something that would compensate for different size (diameter) tires than OEM.

I can hook a scope up to the car, what would you like to see?

[monroe74]

Originally Posted by dcb

we should add in the area under the curve where the injector is opening AND when it is closing

I realize that you and Yoshi both see a need for this kind of correction/compensation, and I hesitate to disagree, but I wonder if it's necessary, or correct.

There is mechanical inertia on both ends of the cycle (opening and closing). And I have a feeling these two effects net to zero.

I think your nice drawing provides a way to see this. If you sum the two red regions, it looks like the result is 1ms of full flow. If so, then we're getting the same total flow that we would get in a universe with no mechanical inertia.

[ttoyoda]

Yup, thats why a large value resistor and a zener (which should be forward biased and carrying 650 micro amps at the pulse peak.

I have never looked into this, but do you know if the specific zener that is used with the MPGuino "turns on" fast enough to actually clamp that peak? Obviously for steady state that is true, but the risetime on that peak looks "fast".

[monroe74]

Originally Posted by MilesPerTank

I'm not running OEM tires so I will probably do that calibration with a GPS unit.

Here's another way to do it. Google Earth has a nice Ruler feature. You can use it to find the exact distance between arbitrary landmarks. It seems to offer a lot of precision and accuracy. For example, I can use it to determine that I live on a street that's 268.01 inches wide. Or that my driveway is 10,890.26 inches (0.17 miles) from the corner.

[dcb]

Originally Posted by monroe74

I realize that you and Yoshi both see a need for this kind of correction/compensation

Really I don't see the need for it, I've been questioning it from the start and have never coded for it. There may be some area under the curve that my crude triangulation does not encapsulate, and I would love to hear more details from the "subtract a certain amount from each pulse" proponents though.

[ttoyoda]

Quote:
Originally Posted by MilesPerTank View Post
I'm not running OEM tires so I will probably do that calibration with a GPS unit.

Here's another way to do it. Google Earth has a nice Ruler feature. You can use it to find the exact distance between arbitrary landmarks. It seems to offer a lot of precision and accuracy. For example, I can use it to determine that I live on a street that's 268.01 inches wide. Or that my driveway is 10,890.26 inches (0.17 miles) from the corner.

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. 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. You cannot even resolve where the sloped edge of a curb, or the edge of a road starts from those views.
What is the accuracy of GPS now, +/- 30 feet? So that is 60 feet uncertainty at your start and your end position. That is 1.1% uncertainty if you test over one mile. .11% if you test over 10 miles, but you had better be driving in Kansas to get a flat straight road 10 miles long.

[MilesPerTank]

Originally Posted by ttoyoda

I have never looked into this, but do you know if the specific zener that is used with the MPGuino "turns on" fast enough to actually clamp that peak? Obviously for steady state that is true, but the risetime on that peak looks "fast".

You could wire a pair of Schottky's in a bridge for a lower capacitance (higher speed) solution if you fear the fly back!

I'll probe it and see what it looks like standard.