This is very important.
The PWM freg must be low enough to give the
time necessary turn an injector on and off.
This is done in the back ground in the Arduino
and the MM.

No direct program action is required once it is set
up. The longest  the MM will do is 50 msec.
As far as I can tell the longest the Arduino will do
is 33.3 msev. Said another way the max time available
for the injector pulse width.

This circuit does the same thing but as long as
you want to what ever you want.

It requires an 8 bit port  for two injectors
but as I recall the same D to A is available
in a 4 channel version that will handle 4 injectors.

The fuel injectors will continue to work if it
still has power even though the computer dies.

It requires a 10 HZ oscillator (100 msec injector
window) but that could be done with another
555 or come from a Pin on the MM. The injector
pulse width can be updated ten time a second
or less often at your option.

The 8 bit port sets the pulse width to one part
in 256 but once that is done this circuit handles
the injectors from then on in the back ground.

This is a classic example how sometimes it is better to add hardware rather than software on low volume computer based products. Software cost and programming time becomes the greatest  expense.



Paul Lamar

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