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.