[Diy_efi] Direct fire from wasted spark?

[steve ravet]

Derek wrote:
> 
> My fuel management computer only has 4 coil outputs, and I have 6 cylinders. Is
> it possible to made some sort of electrical circuit, that will switch the
> ignition outputs between two coils, based upon a signal from the cam sensor? So
> basically, given the firing order (1-5-3-6-2-4), and outputs from the ECU of
> IGN1, IGN2, IGN3, it would go like this:
> 
> IGN1-Coil1
> IGN2-Coil5
> IGN3-Coil3
> 
> Then the box switches the outputs, so that they go like this:
> 
> IGN1-Coil6
> IGN2-Coil2
> IGN3-Coil4
> 
> It would switch every crank rotation.

It's certainly possible to multiplex the ignition outputs, but the exact
circuit is going to depend  on the waveforms you need to fire the coils,
and the waveform you get from the crank sensor.  You could do it all
with CMOS logic, or you could use a small PIC microcontroller and do it
in software.  
You'll need a circuit like this duplicated 3 times:

              _____
IGN1  -------|     |-----Coil1
bank  -------|_____|
              _____
IGN1  -------|     |-----Coil6
!bank -------|_____|

Where the box is an AND gate, and bank is a signal that toggles for
every revolution of the crank, and !bank is the inverted version of
bank.  The easiest way is to probably use a J-K type flipflop on IGN3. 
It will need to incorporate the cam sensor, though, to make sure the
circuit stays synchronized.

--steve


-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com

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