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sensitivity/max load of IGN output

Posted: Tue Oct 06, 2009 8:54 am
by pigga
Hi all,
I would like to convert a SPI injected engine to MS, using the new microsquirt module.
I am a little bit hesitating about how to hook up the ignition coil to the system:
I am using an "active driven coil" Bosch type, something similair to
Image
The module should provide a "logic output". But as I have seen, the "Ign out" pin of the Mircosquirt module nearby directly leads to an output pin of the MS cpu.
The imprint on the Module says "max load 5mA". 0.005A are really, really low value (or do you mean 0,5A?). Further more I suppose that the Bosch module provides a 12V logic output. The MS CPU is running at 5V.
Can I hook up the module to the "Ign out" of the module, or is this to risky? As an alternative, I would put a tiny transistor in between as "Amplifier", just to keep high loads or voltages away from the CPU.
Any help is appreciated!
Thx a lot,
Thomas

Re: sensitivity/max load of IGN output

Posted: Wed Oct 07, 2009 6:26 am
by Matt Cramer
5 mA is not a misprint. Many ignition modules can work with this as it is since the signal is just triggering a transistor inside the module. But there's no harm in building a transistor buffer circuit to get a stronger signal.

Re: sensitivity/max load of IGN output

Posted: Wed Oct 07, 2009 7:40 am
by pigga
I was a little bit confused about the "5mA". But you are totally right: This is fairly enough to trigger a transistor's base.
In my further applications I always used a 1k Pull-Up to provide a clean square signal to the ignitor module. Probably some kind of overkill, bit this works fairly well. I never tried to hook it up as a "logical port".
I have a slight headache so lead up some wire from the µC's pin directly (ok with a serial resistor in between) so somwere outside the ECU. If something outside the ECU goes wrong (any short circuirt with 12V leading wires for example) the µC might get fried. I think it will be the best to use a simple resistor as an amplifier and as a cheap life-ensurance for the Motorolla cpu.
Thanks a lot for your support!
Thomas

P.S.: To prevent other users from doing unsensible things, it could make sense to point it out more clearly in the manual? At the 1st glance it isn't 100% obvious if its the documentation of microsquirt or of the module. At least some unexperienced userd could get confused.

Re: sensitivity/max load of IGN output

Posted: Thu Oct 15, 2009 11:20 am
by pigga
Hi all,
I just took a 2N2222 with a 1kOhm pull up and it works fine.
Thx for the response.
Thomas