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Old 06-12-2008, 08:52 AM   #251 (permalink)
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RuHaSs, thanks man, PM sent.

MPT, try unplugging and plugging in the power, or do like I just did and connect LCD pin 2 to arduino pin 15, instead of directly to the 5v bus, so it can reset the LCD properly. You need the latest code for that (see latest updates a few posts back). The problem, if it is what I think it is, is that the LCD likes to be initialized once and only once after being powered up. Resets and code updates to the duino result in the LCD getting a new set of initialization when the duino reboots, even though the LCD didn't reboot. It isn't a problem if you can power cycle the whole unit but it has been enough of a PITA in development that I finally took a pin for it.

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Old 06-12-2008, 09:45 AM   #252 (permalink)
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Quick update: Modified the instant mpg function so it better corresponds with the trip mpg.
Labeled as v0.61, code updated.
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Old 06-12-2008, 04:46 PM   #253 (permalink)
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I took some measurements on the currents with a current probe and scope.

brightness zero 37mA
brightness one 55mA
brightness two 73mA
brightness three 90mA

I can see that base pin is being PWM'd at 500Hz. Peak current is 90mA for all but brightness zero (no base current pulses). Above I just wrote out the mean currents.

So at full brightness you're looking at :
*65 C/W for junction to air unheatsinked 7805 TO220 package

(( Vin - Vdiode - 5V ) * 90mA ) * 65C/W = rise over ambient

Plugging in Vin =14V, Vdiode = 0.7V you get 48.55C. Max junction is 125C. As long as you're under (125C-49C =) 76C / 166F ambient you will be Ok.




I also hooked up a function generator for a variable pulse width square wave to make sure the pulse is being detected properly. What is your idea behind the IC or rpm variable? I fed it a 10Hz signal and the IC was 20. 50Hz the IC was 100. Etc....

Last edited by MilesPerTank; 06-12-2008 at 06:11 PM.. Reason: .
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Old 06-13-2008, 09:34 AM   #254 (permalink)
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Nice MPT, I hope to get it to shut off the backlight again when it is unattended so hopefully we will be at 37mA by the time the car interior ramps up. Still 165, that is pretty hot

re: injPulses (count), I haven't really looked at it, but eventually we can compute RPM from it, at least for many cars, but I would expect a number equal to the number of rising edges in a half second? So if you gave it a 10hz signal it should say 5, and a 100hz signal IC should say 50.

...
attachInterrupt(1, processInjClosed, RISING);
...

void processInjClosed(void){
tmpTrip.injHius += elapsedMicroseconds(injHiStart);
tmpTrip.injPulses++; //IC incremented here, and displayed and reset every .5 second
}
...
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Old 06-13-2008, 10:59 AM   #255 (permalink)
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If its ever 166F I think I'll have larger problems on my hands then the MPG computer going into thermal shutdown. I've never run peak brightness outside of testing anyways.

From what I saw regarding the IC its off by a factor of 2. May as well just multiply it by 60 (seconds) and display it as an RPM. We can see if its correct pretty quick.
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Old 06-13-2008, 11:27 AM   #256 (permalink)
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Quote:
Originally Posted by MilesPerTank View Post
May as well just multiply it by 60 (seconds) and display it as an RPM. We can see if its correct pretty quick.
It's worse than that (and rpm has to wait). You have to factor in the number of cylinders, weather or not it is TBI or MPFI, if it is bank fire MPFI, or if there even exists a correlation between the number of injector pulses and the number of engine revolutions for a particular vehicle. The nice thing about trying to deduce RPM from the injector signal is that it simplifies hookup, but I really don't know at this point how may cars it won't work on, and we have to ask some unintuitive questions during setup.

If Yoshi is right though, we will need to make sure we get the number of injector pulses right, because there is a mechanical delay in opening the injector (but no mechanical delay in closing the injector?!?)
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Old 06-13-2008, 12:09 PM   #257 (permalink)
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http://www.msextra.com/manuals/MS_Ex....htm#constants

That gives you a bit of an idea of what injector opening time is like. You can pretty much just say 15msec to open the injectors and be close enough for most cars. When the injector closes you could just subtract that amount from the calculated open time.

I really need to get the stuff to build one of these, closest chip I have right now is an atmega32 chip and I don't feel like trying to recompile everything to run on it. I do have several 16x2 displays as well as some 40x4
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Old 06-13-2008, 12:41 PM   #258 (permalink)
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Ok, I need a picture. So I think the way this works is that we should add in the area under the curve where the injector is opening AND when it is closing, and that looks like it adds up to roughly 1mS. Yoshi came up with .5 mS, would like to understand that discrepancy.

But FIRST, we need to make certain that we can calculate the number of injector pulses correctly.

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Old 06-13-2008, 12:49 PM   #259 (permalink)
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http://www.automotivetestsolutions.c...rWaveforms.htm

Look at the size of the kick back when the inductor inside the injector flys up.

65V!
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Old 06-13-2008, 12:56 PM   #260 (permalink)
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Yup, thats why a large value resistor and a zener (which should be forward biased and carrying 650 micro amps at the pulse peak.

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