Additional Injector Controller

[Ian Habicher]

>You can run the 555 as a mono-stable timer with the external signal
>used to start the timer. An ignition signal could be as convenient
>to use as any if the injector is a long way upstream.
>If you have a distributor ignition, you might want to feed the
>trigger signal through a "divider" so that the injector fires only
>once per rev or even two revs.  (A 4017 decade counter is cheap and
>simple.)

It's a twin-rotor Wankel with batch-firing plugs that fire every half rev.  
So the leading ignition signal would be perfect.


>Injector characteristics will determine the operating cycles
>(e.g. min/max open times) as much as the engine speeds.
>
>The duty cycle is relatively easy to set by altering the voltage
>levels that the 555's comparator sees.

Cool, I don't know much about the 555 so that's what I need to learn. I have 
access to a pile of books on it that are hard to digest and tie my brain in 
knots more than the price lists of commercial AICs :)

I believe it's the 'threshold' pin voltage that's varied to control pulse 
length right?


The "standard" 555
>application uses resistors to provide those levels.
>Look at the block diagram of the 555 closely and you'll see that
>there's a great deal of flexibility when playing with these circuit
>building-blocks.

Yeah it's great that's why I want to use it.  Actually driving the injector 
sounds easy, I'll just use a big ass MOSFET and resistor and one of those 
Nat Semi injector drivers.  Or even just the MOSFET itself if it works.  
Simplicity is king if it helps reliability!

>You probably want to suppress the output below certain manifold
>pressure levels; an analogue comparator can be used to hold to the
>RESET on the 555 when the MAP sensor's output is too low. i.e. you
>"clip" the output before the open-time on the injector becomes
>useless.

Exactly, my stock fuel system gives up at 8 PSI boost, I think about 3.7 
volts on the MAP sensor, and I want the AIC to pick up there.  Of course, 
I'd like to make this on-threshold adjustable with a pot.

Can I set up the 555 itself to provide this?  If the circuit produces a 
lengthening pulse with increasing MAP voltage, then I should be able to set 
a threshold voltage where no pulse is generated... right?


Thanks to everyone on the list for their help, you guys rock!

Ian
87 RX-7 Turbo II


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