Paul,
        A better mass air sensor to use is the unit found in ford V8
trucks from 97 and up. Many of them in salvage yards. They were for
     engines of
        220 to 260 hp putting them in the flow range we need. Also very
light and reliable. Just don't get one from the supercharged trucks, as
     they
        are 90mm diam. Larry

        Thanks for the tip Larry. Are they mechanical like the Mazda or
        electronic? The electronic are harder to use as they are
tougher to interface with the 555. The Mazda unit is just a trap door
     connected to
        a pot.

        --
        Paul Lamar ...No rotor no motor.


        Paul,
        Pin out attached.
        Larry

        The problem is 5 volts is high airflow and the 555 fed 5 volts
     would be
        narrow pulse. Zero volts would be a wide pulse out of the 555.
     What you
        one must do is come up with a circuit that reverses that and
probably increases it to 12 volts. Using the Mazda simple device you
just wire the pot backwards.

        I am not saying it can't be done. Just more trouble.
        --
        Paul Lamar ...No rotor no motor.

        I would call such a circuit an op-amp.  Inversion and scaling
in one step.

        Bob W.


        --
        N93BD - Rotary Powered BD-4 - http://www.bob-white.com
        3.8 Hours Total Time and holding
        Cables for your rotary installation -
http://roblinstores.com/cables/


        Sounds like you are the man for the job Bob. Care to do a
     schematic and
        make a prototype on a plug board?

        Here is what the Mazda unit would look like along with the
original Chaparral 2D  ram air box from 1965.

        --
        Paul Lamar ...No rotor no motor.

        OK, I'll draw up something 0-5V in, 12-0V out and build a
breadboard circuit.  It may be a few days as I'm trying to finish up a
couple of other projects.

        Bob W.

        --
        N93BD - Rotary Powered BD-4 - http://www.bob-white.com
        3.8 Hours Total Time and holding
        Cables for your rotary installation -
http://roblinstores.com/cables/


        Great Bob.
        Thanks.

      ------------------------------------------------------------------------

        Here are the pin outs and resistance data on the Mazda
mechanical air flow sensor if you want to keep it as simple as possible.
        The sensor air flow area is about 5 square inches so it is a
bit of a restriction
        on a P-port engine with two... 1 7/8 ID runners have 5.52 square
     inches
        total  area. How much that is going to affect the power is hard
     to say.
        I intend to get the prop dyno working with the P-port RX8
engines so perhaps I will find out.

        The resistance varies between 50 and 500 ohms so the 555 pulse
width with a 100 uF cap should be in the right range (1 ms to 50 ms) I
am not sure this
        is going to work. It would be better if the pot was higher
     resistance.
        I'll have to mock it up on the bench.

      ----------------------------------------------------------------------------

        I am coming around to the hot wire and op amp approach.
        I suspect that a 100uF cap may not be practical for drift
reasons and temperature
        change reasons.

        Here is a great little opamp calculator. http://www.bcae1.com/
        Scroll down to about the middle of the page.

        It will also work with a FreeScale MAP sensor if you don't want
     to use
        a mass airflow sensor.

        Here are hot wire sensor pictures from a Ford Escort.
        --------------------------------------------------------

        Bob, what do you think of this idea? Small daughter PC boards
50 mm (2") by 26 mm (1") with
        the op-amp, the 555 and the FET on them for each injectors.
Modular. If one fails
        you carry a spare and plug it in.  Makes things easier to
trouble shoot as well.

        The 50 by 170 mm (7") 3 rotor motherboard can have the pilot
        controls on it such as the start
        enrichment switch and the leaning pot. The whole works can be
        mounted behind the instrument
        panel. This should drastically reduced the wiring the installer
     must do.

        Also I am thinking that coax cable could be used for all other
        wiring. Coax is shielded
        and if it is Teflon it is hard to burn through in a fire.
Nothing says you cannot
        use coax for DC. Also BNC connectors are cheap and they are
shielded.

        It is about a buck a foot but cheap insurance against RF
     interference.
        Lots of people have had problems with that lately.



        Paul Lamar ...No rotor no motor.


     I don't think coax is necessary as I don't think any other part of
the circuit is going to be a controlled impedance environment.  Coax is
     useful (required) where power transfer is critical from one device
to another (antenna systems and other high frequency systems (MHz+).
     Tefzel (standard Aircraft Spruce) shielded wire should be perfectly
     suitable for the signaling in this kind of system.  The power and
ground don't need shielding - but the wire needs to be plenty big, and
there should be some filtering on these leads.  It might be a good idea
to shield the signal (sensor) and injector wires.  Ground the shield
only at the control box.


     Regards,

     Matt-

     All true Matt but I like the sledge hammer approach to RF
interference. Do IT all in coax :) Using BNC connectors it is easy to
disconnect things
     for trouble shooting and the grounding is built in. Cost is the
only drawback but this is an airplane for heavens sake :)

     With the simple 555 system you have two wires coming from
     the two mag pick ups and four wires going to the injectors. Of
     course the top
     of the injectors are connected to 12 volts. The FET's merely ground
     the bottom
     side of the injector coils.

     BTW it is very very simple to mechanically change the injector
     timing by rotating the
     mag pick up steel plate relative to TDC.

     --
     Paul Lamar ...No rotor no motor.


I don't like fat coax because it's heavy and bulky...  I have seen
plenty of improperly installed BNC connectors.  DB (15,25) connectors
are easy to install and remove as well.  But, it's your airplane..  :)


Matt-

RG59/RG58  coax is only about .2 inch in diameter.
Probably a dozen people have had trouble trying to solder a zillion
wires to DB connectors. Yes I know you can get crimp on style but the
wires are two small for the current levels we are running. The shock
and hold injectors require about six amps. People building airplane are
not necessarily electronic technicians. We must keep it very robust and
very very simple. You want DB buy Tracy.