Schematic as drawn has several  errors:

1) 1N2004 should be 1N4002 ??

2) Gain control on Op-Amp between Mass Airflow Sensor is miss drawn.
     Pot does nothing, gain of circuit is fixed at +1.

3) Output for GPH gauge needs to be an integrator, not a peak detector.
You want measure the "average of the on time" to get GPH.

4) There has to be some sort of snubber circuit across the injector coil,
otherwise the turn off voltage spike will destroy the FET.

JCP

--- On Wed, 4/8/09, Rotary Engine <rotaryeng@earthlink.net wrote:
From: Rotary Engine <rotaryeng@earthlink.net
Subject: FI Control
To: "AAA Put this in the To box" <rotaryeng@earthlink.net
Date: Wednesday, April 8, 2009, 10:09 PM

I went to some of the RX 7 groups online to find out the best way to
control
FI.  I am looking at Megasquirt as a plan B or C if the 555 analog system
does
not work out.  I guess there is manifold pressure which is not stable on a
P
Port.  Ther is  Mass air flow which is being proposed for the 555 system
and
is
supported by Megasquirt.  The RX 7 guys seem to think the MAF sensor could
impead the air flow to make big horse power.  200 to 250 HP does not seem
to
be
big HP when they are getting a lot more out by turning the engine faster.
How
does TPS or throttle position sensor fit into this?  Thanks for any help

Joe Berki
Limo EZ 13b P Port



As long as the mass airflow sensor is around 5.5 square inches it should
be
fine.
That is something about 2.625 or 2.75 inches in diameter will give around
250 HP. The throttle position sensor will not work with the 555 system
not is it needed.
--Paul

Paul

How would the  mass flow sensor work with a turbo charger on the front
end?  I Think that the MAF sensor would be calibrated for ambient
pressure N/A applications.

Doug in Japan

The 555 system has a provision for scaling the airflow signal.
The gain of the op amp can be adjusted.
It responds to mass flow only and not pressure per se.

Paul Lamar


Schematic as drawn has several  errors:

1) 1N2004 should be 1N4002 ??

2) Gain control on Op-Amp between Mass Airflow Sensor is miss drawn.
      Pot does nothing, gain of circuit is fixed at +1.

3) Output for GPH gauge needs to be an integrator, not a peak detector.
You want measure the "average of the on time" to get GPH.

4) There has to be some sort of snubber circuit across the injector coil,
otherwise the turn off voltage spike will destroy the FET.

JCP

Thanks John. Do you have a suggestion for fixing the op amp circuit?
If you don't mind use ms paint to draw in the proper resistors. I think
the
10K resistor is mis drawn to the output pin instead of the input pin.

I also think the snubber is built into the FET. I just failed to draw in
the diode.  At least I have not failed one yet. I added it to the
schematic.
I forget to fix the 1N4001 diode number as that came up already.

Here is the schematic again with the diode and the snubber fixed.

Paul Lamar

Hi Paul

Is this what JCP means on moving the 10K to the input?
I hope the attachment size is ok.
Any chance of a component list with current values?

Clive C

JCP has not responded yet.
I made a mistake in the op amp dwg. The 10K was supposed to be connected
to the minus input on the op amp. I need to fool with it
a bit more to get the resistor values right. Same with the list.
Most are on the schematic.

Here it is fixed.

I have the mass air flow sensor set up on the bench.
Works like a charm. Very stable and changes slowly
along with the speed of the blower. Works great.
I need to get a more powerful blower to test it further. I only
get a volt or so by blowing on it. It is zero volts
just sitting there powered up with 12 volts no airflow.

Paul Lamar

Paul,
If you up date the schematic could you include the digikey part number for
components?  I think it will help those that are making this their first
electronics project.

Joe