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Karri's "Wildcat" EMS for ModICE enclosure 
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Fred wrote:
Use FET-drivers for ignition outputs, and keep the voltage supply to them configurable in hardware, too.
KW1252 wrote:
Anyway, the actual transistor for the ignition module driver is going to be a FET and not some odd throughhole BJT. The provided schematic was a nice gesture from Bosch, it eliminates a bit of guessing.

Karri, with all due respect, please read my posts, and pay me some respect in these matters. While you've been off in a cardboard box looking for your old TA card, Andy, Dan and I have been doing some heavy-duty R&D and have most of this stuff nailed down hard.

I really need to start on the FreeEMS hardware compliance documents such that I can just point at them.

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Tue Dec 03, 2013 8:44 am
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Yeah, I read and acknowledged that FETs should be used. If it didn't come out in the text correctly I apologize.

I'm a bit at loss here. Bosch datasheet states +5v signal on the darlington base. Then again I've read about the +12 volt needed on darlington here. So is the manufacturer wrong with the numbers?


Tue Dec 03, 2013 12:07 pm
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The Bosch ignition drivers are Darlingtons the same way a VND5N07 is a MosFET - lots of extra circuitry for protection etc. There have been tests done on the MSExtra site, and the BIP373 simply shuts down at 6v on the gate.

Edit - Fred's comment on the ignition output was not to use a FET, but rather a FET driver. Different beast.

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Tue Dec 03, 2013 2:54 pm
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I think the key difference is the Bosch unit is a triple-tier darlington vs. the regular two-tier; 22mA vs excess of 300.

I guess the question boils down to this: I understand the reasons behind maximum flexibility, but it too is a coin with two faces. It increases the board complexity, it adds to the overall single points of fault and introduces the chance of a configuration error. These have to be weighed against the hardware choices available for each function. The merits and drawbacks need to be considered. The older ignition components are plentiful and not expensive, but again, it does pose certain compromises to the design and the bottom line is, they are all there to do the same job. There are already a number of designs with incredible flexibility, and it's a good thing. As a whole, FreeEMS covers a huge range of different engine setups. In my design the goal is to have a selection of hardware, which, while "focused", would not limit functionality. Having less variables to consider will also help in the inevitable troubleshooting in development and use. This is how I distinct my design from the others. I hold each of them in great esteem. Each of them is the product of their own designer and a pursue of their own goals.


Tue Dec 03, 2013 4:48 pm
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DonTZ125, thank you, your edit nailed it.

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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!


Tue Dec 03, 2013 5:54 pm
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I don't think a 150 dollar ignition module should be a deal breaker in a performance engine build, but just for the benefit of those wanting to keep the original equipment, I guess a concession could be made. How about an ORing schottky for +5v and an externally switched FET driver for +12v(ground a pin in the header for +12V or left unconnected for 5v) to switch between levels? At logic level a schottky diode does not have to dissipate a lot of energy and the few hundred mV drop is manageable.


Thu Dec 19, 2013 12:53 pm
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