> Do we have any 555 experts on here?
> I am feeding the control voltage into pin 5
> and the duty cycle seems to be limited to 0% to 50%.
> Over 50% and the pulse width jumps to max.
> --
> Paul Lamar ...No rotor no motor.
Paul
Check your input signal carefully to ensure it is not going more negative
than gnd. This can forward bias the substrate junctions. Also input pulse
width at the upper threshold level must be shorter than the output pulse.
regards, Robert
Thanks Robert. I did that. Did not help. I have some TI TLC555IP CMOS 555
on order
from Digikey. In my experience CMOS are less prone to glitches.
--------------------------------------------------------------------
Bingo!!! The 79 cent TI TLC555IP CMOS 555 is the hot tip.
A bonus for a CMOS chip is it's high output drive current of
15 ma source and 150 ma sink. It is not your grandfather's 555 or even
your dad's for that matter. That should be enough to drive the injector
FET
directly.
The control voltage is perfectly linear from 1 volt to 9 volts 1 ms to 9
ms.
which is exactly the range we need. Perfect!!!!!
Next step is getting it to work with Bob's op amp
and we will have a two buck 555 fuel injection system :)
Just about any 0 to 5 volt mass airflow sensor will work.
To be continued after OSH.
-----------------------------------------------------------
I was near Fry's after supper so I picked up a NTE 67 FET.
Worked like a charm. The stock Mazda yellow injector clicks between 1 msec
and 9.5 msec which is about 95% duty cycle at 6000 RPM.
Of course I am not feeding it with fuel yet but that will
be the last bench test. That stock Mazda injector is actually made
by Denso. Its pretty good. I don't know the flow yet of course.
We will pee into a calibrated measuring cup to find out.
That NTE 67 cost about seven bucks at Fry's but I am sure Digikey
or Mouser has them for less than half.
Not counting the injector total cost so far is under about
six bucks per injector. We still need the op amp and mass airflow
sensor but only one for all four injectors. The op amp will
have to wait until after OSH.
Hard to beat this system for low cost.
An Ellison or Weber is about $1000.
Paul Lamar ...No rotor no motor.
Paul,
Do you have a schematic for the Op AMp circuit? What kind of gain are you
looking for?
Joe Berki
Limo EZ
Yes we do. Bob White did it. We need a gain of two.
The 555 pulse varies from 1 msec to 9.5 msec
while the mass airflow sensor puts out 0 to 5 volts.
We will make the gain adjustable for tuning purposes.
Maybe one pot is all we need for leaning. The same pot that
changes the gain. The 20K feed back resistor would become the leaning
pot.
--
Paul Lamar ...No rotor no motor.
Paul,
We may want to incorporate a circuit to richen the mixture above a certain
load point. In other words, using a voltage comparator, and a multiplier,
add in additional fuel at the upper end of the mass air flow readings. Using
this trick you can get a non linear fuel amount related to the mass air
flow. We need to make sure the system auto richens a little on the upper
power band to keep the engines safe at WOT. As the plane climbs, the mass
air voltage lowers based on the air density and the circuit returns to
normal. Give it full throttle at low altitude and it will fatten up and be
safe.
Larry
That is pretty easy to do. When the Mass airflow sensor voltage gets over say
4.5 volts a zener diode kicks in with some more fuel.
Paul Lamar ...No rotor no motor.
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