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coil ignitor noise 
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Joined: Sun Oct 30, 2011 8:57 pm
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I've got a COP setup for my tractor, and it all seems to work fine, except when it is all hooked together.
I created a disk with 8-1 magnets on it, and use a hall-effect sensor to read it.
The magnets are setup such that as they approach the sensor it goes high (3v),
and as it passes it goes low (0v). This works great, my only issue was at higher RPM,
it was running out of time to do the spark, but turns out a floating point calc took ages using the GNU emulation,
and I just eliminated it and now I have forever to setup the spark.

So what I'm using to ignite the coils are two Duraspark ignition modules.
I'm using those because I had one already, and I wanted to avoid the high voltage issues with triggering the coil.
The duraspark module can be fired using the "orange" wire by pulling it to ground for .5 msec,
when it goes back high (.6-.9v) the coil will fire.

To pull the orange wire low, I use a darlington transistor, driven by a pin on the MSP430.

My problem is when running it the coil is firing "spuriously", which appears to be noise coming from
firing the coil at is normal time, following that it can fire another 2-3 times sometimes.
I'm certain that it is a noise issue with the back EMF, but I thought using the duraspark I would not
get this kind of issue.

My thoughts are I will need to use an opti-isolator to drive the orange wire transistor,
and then I can isolate the power supply of the MSP430 from the 12v battery.
I don't happen to have one handy, is that my only solution?


Sun Nov 06, 2011 1:10 am
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Quote:
The duraspark module can be fired using the "orange" wire by pulling it to ground for .5 msec, when it goes back high (.6-.9v) the coil will fire.

This sounds very very wrong to me. I'm 99% sure (I DON'T know, but this is a GOOD guess) that you will need to use a pull up on that input. Pull it to 5v with the lowest value resistor your darlington can ground out continuously without overheating. 1k would be a good start. I bet this is your problem. Other than that, you might consider using coax and rerouting wiring if you've not done so already. There is something resembling a guide here:

viewtopic.php?f=54&t=1349

Let us know how you get on!

Also, LOL @ doing FP calcs. You want to use fixed point math on these little toys :-)

Fred.

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Sun Nov 06, 2011 11:46 am
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DIP8 - Involved

Joined: Sun Oct 30, 2011 8:57 pm
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Not sure where you get 5v to fire the duraspark, I scoped the signal coming from the distributor pickup,
and it doesn't get near 5v. I have no problem firing the coil, a test setup fires it fine from the micro
at any rpm.
The problem is that the hall-effect signal that the micro sees is disturbed, but if I scope the signal
that comes from it the sensor, it is normal, but the micro is getting the interrupts triggered anyway,
and then it is firing the coil inappropriately.

I'm wondering if the duraspark is putting noise on the orange wire that comes back into the microboard,
and it isn't isolated as I thought, because the noise wouldn't matter to the distributor pickup,
although I have not seen it on the scope.
I'm quite frustrated.


Sun Nov 06, 2011 5:44 pm
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I see! Well, that is definitely not how your original post read at all. In light of this new and more thorough information, I would recommend a few things:

1) Make sure your power is very clean, ground included.
2) Make sure that you're using coax cable for your RPM input as per the thread that I linked.
3) Make sure you present a suitable input impedance to the RPM signal source to help eliminate stray noise with weak energy content.
4) If it's a hall effect output, make sure it is pulled high as they are usually done in open collector style
5) To be clear, if your coil is firing at wrong times and you claim it's coming from the micro, then you NEED to add some sort of concept of sync/loss into the code such that if it gets a stray signal it just stops running rather than bending a rod or blowing a head gasket.
6) RFI can trigger the micro pins directly. Make sure you have the device housed in a metal enclosure, aka partial faraday cage.

And probably other stuff too.

Fred.

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Sun Nov 06, 2011 8:55 pm
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DIP8 - Involved

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I dug up an opto-isolator transistor, connected it to the micro output pin,
and have it drive the darlington to pull down the orange wire, and now it appears to
work without issues.

I agree some safety/sync issue would be nice, but frankly there isn't much you can do if you
don't have a reliable hall-effect sensor input. I check for the missing tooth every time around to sync,
so if it isn't found it isn't firing the coil, but this is no help if it appears to have missing tooth when it doesn't.
I could add a second sensor/magnet to the disk that is only one TDC, so it would be effectively is a check against
the missing tooth, but it would have to be much closer to the center (not even sure I have room), so its accuracy
would not be as good with less travel around the magnet.
One thought I did have was to add another magnet between the two before the missing tooth, so now we have half-time
followed by double time. That would be harder to create with noise, but no doubt still possible.

I'm not sure how fast the engine can accelerate, such that checking the time between magnets to verify
they are within a reasonable range would help. I know the engine can slow down fairly quickly when its
got a load on it.


Sun Nov 06, 2011 10:57 pm
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I've done some work on this recently, and except while cranking, the acceleration isn't much, even WOT in neutral. So yes, it's worth checking each pulse relative to what it should be compared to last time (ie, approx same or appox double), definitely.

As for the sync, just count the number of non missing and make sure you are never under or over the correct count when you get the missing one. if so, dont reset sync, reset counts and try again to find it from scratch.

You're right that you need a good signal, but you also need to know that when some wire comes loose and starts causing issues that you don't fuck the engine in the process of finding the wiring fault.

Fred.

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Mon Nov 07, 2011 3:07 am
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DIP8 - Involved

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http://www.youtube.com/watch?v=Nngf38B-jaY

here is video showing the parts and it working!


Tue Nov 08, 2011 4:37 pm
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LOL! I love it, so tiny! :-) That PCB is about the same size as our CPU! And the fact that it's

Image

Powered by duracell is absolutely hilarious/awesome :-)

Fred.

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Wed Nov 09, 2011 12:32 am
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The 9v battery was just for testing, you really think I'd need a 9v to run the tractor? that is funny.

I built the completed board with a 10-16v-5v isolated DC-DC, with the opto and darlingtons.
I still got noise with this, and it turns out the orange wire isn't the issue, but the ground.
However, in the testing video, you can see I've got an open spark about an inch long,
which just invites massive noise, so once I connected it to a spark plug inside an engine,
it appears to work without issues now.

My final concern is the coils. While the Duraspark ignitor was cheap and easy, it wasn't designed for COP,
it has no dwell control, so the power to the coils is aways on.
I need to use a resistor to control the coil amps. A 1.2ohm gets really hot running one coil at about 4amps.
What amps do the Dodge 2.7L coils need?

Fred, it looks like you are one man show here, where is everyone else?


Mon Nov 14, 2011 3:07 am
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nimblemotors wrote:
The 9v battery was just for testing, you really think I'd need a 9v to run the tractor? that is funny.

No, but it's funny, even in a test context :-p

Quote:
I still got noise with this, and it turns out the orange wire isn't the issue, but the ground.

No big surprise there :-)

Quote:
My final concern is the coils. While the Duraspark ignitor was cheap and easy, it wasn't designed for COP,
it has no dwell control, so the power to the coils is aways on.

That's nothing to do with COP... you're supposed to control the dwell yourself! I take it your code is very simple and doesn't do that? There might be some systems that can sync with your ignition edge and do the dwell for you, not sure what, though. Otherwise, add code to handle that...

Quote:
I need to use a resistor to control the coil amps.

That's not really an acceptable solution for a variety of reasons...

Quote:
A 1.2ohm gets really hot running one coil at about 4amps.

This being one of them. Also, feeding a coil 4 amps continuous will probably cook it eventually, and drain your battery/load your alternator in the process.

Quote:
What amps do the Dodge 2.7L coils need?

About 4 milli seconds of amps :-p You have to do it with time. You switch a coil to ground for X ms (2.5 - 8) and then release, when you release, it fires. then it gets a rest before you do it again. it needs the rest... :-)

Quote:
Fred, it looks like you are one man show here, where is everyone else?

In the FreeEMS and SECU-3 sections getting shit done! :-)

Fred.

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FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Mon Nov 14, 2011 11:10 am
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