Additional Injector Controller

[Bernd Felsche]

steve ravet tapped away at the keyboard with:

> There should be lots of app notes and data sheets for the 555 on
> national semiconductors WWW page.  You can set up a circuit where
> a variable voltage controls the duty cycle output.  synchronizing
> it to another injector might be more complicated.  While you're
> there look for op amp notes also, between the two you should be
> able to get what you want.

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.)

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. 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.

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.

-- 
Bernd Felsche - Innovative Reckoning, Perth, Western Australia
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