One of the drawbacks to mass air flow sensors
  is the voltage is more or less proportional
  to the cube of the mass air flow while engines
  need fuel directly proportional to the mass air
  flow. This is handled in most modern  EFI's by the look
  up table.

  As far as I can tell the ZBasic function Exp()
  can get the cube root so in theory no look
  up table is required. It is similar to a manifold
  pressure based EFI system were manifold pressure
  is more or less proportional to the mass air
  flow. Unfortunately therein lie the problems
  we see in tuning as manifold pressure can be
  affected by a lot of things.

  Here is the ZBasicexp() function.

  Type  Function returning Single
  InvocationExp(arg)
  ParameterMethod Type Description
  argByVal  Single  The power of e to be computed.

  This function returns the Single value corresponding
  to the value e raised to the specified power. The
  transcendental value e, upon which the natural
  logarithm is based, is approximately 2.718.
  This function is the inverse of the Log() function.

  A "Single" data type is in the range of
  approximately ±1.4e-45 to ±3.4e+38 and 0.0

  In QB the form is (xxxx)^.5 is the square root
  of xxxx.

  (xxxx)^.333 is the cube  root of xxxx.

  .5 and .3333 are the exponents.

  So the exponent can be selected to linearize
  the mass air flow sensor voltage out put.

  I'll try this in ZBasic shortly,

  I intend to use MAF as the basic means of
  determining the correct fuel flow adjusted
  by EGT based auto tune.

  This is going to make tuning simple if not entirely
  automatic if it works.

  Paul Lamar

  This is a clever approach. I believe you need a differential pressure
  sensor with a static reference in the same environment as the pressure
  probe.  If an absolute pressure sensor is used, you will be
  taking thecube root of (MAP + ram pressure). MAP is normally very
  much largerthan ram pressure. Using a differential sensor (i. e.
  MPX 2050) wouldallow you to subtract MAP before taking the root.

  Victor Roberts

  Thanks Victor. We don't have a choice as the absolute pressure sensors
  are built into Tracy's computer box.

  BTW all standard aircraft
  air speed indicators and air data systems work this way. Static pressure
  is on one side of a diaphragm and dynamic pressure on the other.
  The movement of the diaphragm turns the needle that indicates
  air speed. Dynamic pressure is the square of forward speed.

  Also there is an error in my message above. Can anyone find it?

  Paul Lamar

 cube

 Cary

 And?

 Paul Lamar

  Paul, about "and?"  Actually it is not the cube of the voltage it is
  to the fourth power of the voltage plus an adder. Using the table
  posted yesterday I suggest the following. Add .85 to the voltage and
  take that to the fourth power to get CFM. Note the ,85 constant is
  to provide a slightly larger Cfm at higher airflows making a small
  leaning adjustment. The manual mixture control or wide band O2
  sensor will tune the  output.  If you divide the above by 13.352 you
  have pounds of air per minute. Multiply that by 60 and you have
  pounds of air per hour. divide that by 14.1 and you get pounds of
  fuel per hour. Divide that by injector pounds per hour 39 in my case
  to get percent of on time of the injector. That is then translated
  to pulse width by the flywheel teeth count.

  The math part of the above would look as follows

  Using variable Va as the amplitude of the MAF output voltage

  CFM= (Va+.85)*(Va+.85)*(Va+.85)*(Va+.85)

  Pounds per minute =CFM/13.352

  Pounds per hour = Pounds per minute X 60

  Substituting I get ( ((Va+.85)*(Va+.85)*(Va+.85)*(Va+.85))/13.352)*60

  Simplifying,Set Vb=Va+.85 and deviding 60 by 13,352 to get 4.4937

 And define Pa =Pounds of air per hour

  Pa=Vb^4*4.4937

  Step 2, calculate pounds of fuel per hour Pf= Pa/14.7

  Step 3. Calculate %  injector open time for a 39 pound per hour ford
  injector  = Pf/39

  For an example say the flywheel has 100 teeth on the ring gear, then
  pulse width is the %open time above teeth count. If the flywheel has
  137 teeth multiply the tooth count by 137/100 for the tooth count .

  The assorted constants for injector pounds per hour, baseline
  mixture and flywheel teeth can be defined by their equivalent
  constant which I will call Ce

  ultimately Pulse width is (Va+.85)^4Ce  which is the tooth
  count of the flywheel

  I view this as a conversion factor like changing  inches to  millimeters.
  With one analog to digital conversion for the MAF sensor, A second
  one for the potentiometer for manual leaning (using a  similar
  conversion factor for flywheel teeth) added to the above tooth count,
  and a counter for the ABS sensor.

  So what do you
  think
  george grimes

  I am happy to know that somebody is actually reading this stuff :)

  This is the error I made:
  "voltage is more or less proportional to the cube of the mass air flow"

  It should read:
  "voltage is more or less proportional to the cube root of the mass
  air flow"

  Therefor you have to cube the voltage out of the MAF sensor to
  get the proper injector pulse width. Piece of cake in ZBasic.

  Actually it could be anywhere between the cube root and the fourth
  power. ZBasic does not care. What ever the mass airflow sensor
  curve does that is the exponent you use. Say 3.5. It might not
  be a perfect curve but it will be close enough.

  In QB the syntax is "Pulse width times your constant = (Voltage)^ 3
  to 4"

  This is all opposed to a look up table which is a pain in
  the butt to tune. EGT based auto tune will do the final adjustments.

  The problem with counting the flywheel teeth for ignition purposes
  with the ZBasic is it is not fast enough. That is why I am using an
  external fly wheel teeth counter that updates the RPM count every .6
  seconds. That give the RPM in four digits to the nearest single
 revolution.

  ZBasic could count each tooth if that was all it had to do.

  Using the hardware interrupts in ZBasic to get around that
  is problematic as all sorts of routines and instructions disable
  the hardware interrupts. One of the critical ones is:

  ---------------------------------------------------------
  PWM
  Type Subroutine
  Invocation PWM(channel, dutyCycle)
  PWM(channel, dutyCycle, status)
  ParameterMethod TypeDescription
  channel  ByVal  ByteThe channel to use for PWM generation.
  dutyCycleByVal  Single or integral The desired duty cycle.
  statusByRef  BooleanThe variable to receive the
  status value.

  This subroutine begins or modifies the generation of
  a 16-bit PWM signal on the specified channel. The
  channel must have been previously prepared for PWM
  generation by calling OpenPWM(). PWM
  generation is performed using one of the [WINDOWS-1252?]CPU?s
  16-bit timers, the number of which varies depending on
  the ZX model. The table below indicates the output
  pin for each PWM supported channel.
  The PWM free runs with a given width and frequency until the next
  time it is changed. That frees the processor for other
  jobs.
  -------------------------------------------------------

  Hard ware interrupts  rapidly gets to be a real can of worms.
  That is why I am doing the critical real time stuff like determining
  RPM with the flywheel teeth and firing the ignition with simple
  external hardware like two Hall Effect sensors for a two rotor and
  three for a 3 rotor. The ignition can be advanced with an old
  fashion push pull cable like the Ford Model T. Easy to understand
  and fix.

  Here are some 3D's. I am going to use Hall effect sensors for the ignition
  rather than the traditional mag crank angle sensor as they are much
 cheaper
  and smaller. Therefor I can fire the ignition every ten degrees for
  40 or 50 degrees to improve the fuel burn is it works. I have
  already done a skematic and some R&D on that.

  The RPM flywheel sensor will be the same as the stock CAS or
  the ABS equivalent as hall effect sensors require rotating
  magnets.

  We are still in the planning stages here so a lot of suggestions
  for improvement will arrive once people start thinking about it.

  The $90 Atmel 1290 100 pin board is making it practical and it is
  working to the point where ZBasic software changes are now trivial.

  Tracy does this in assemble language software which is much faster
  but it takes years to be good at it. I want to make this simple
  enough so anybody can learn how to do it in a matter of weeks.

  Paul Lamar


 Hi Paul,
 Suppose you used two trigger wheels spaced say 1/4 to 3/8 inch apart, each
 with two or three "pins" on them. The pins could be 20 degrees apart and
 space
 the two wheels 10 degrees apart. You would have multi spark and redundancy
 in
 firing two ignition systems. The trailing firing off the 10 degrees
 "retarded" system. One par of pickups for each rotor.

 Dale Davies

 Of course we are talking here about simple mechanical  systems
 that do not use the processor for firing the ignition.

 If you mean pins are the same as tits that won't work.
 You need one tit and three Hall Effect sensors to fire
 a 3 rotor correctly. Each rotor fires 120 degrees apart.
 Both plugs fired at the same time.

 In the case of two trigger wheels you would
 need six hall effect sensors. The first set
 firing the leading plugs. The second
 set of three firing the trailing plugs.

 One tit on each trigger wheel.

 Other than that it is a good idea. Hall effect
 sensors are cheap. Adds ignition redundancy
 like dual mags.

 BTW As far as anybody has been able to determine
 there is no HP advantage to split timing
 the leading and trailing spark plugs so this system
 could be set up to fire both plugs at nearly
 the same time.

 Paul Lamar

 Paul,

By firing the leading and trailing together, I would think that would
significantly simplify the design.  Not sure how to do this, but couldn't
you use a repeater circuit to do multi-spark ignition?  Or, better yet, do
it with software.

Mark

Software is out of the question with ZBasic.
You cannot get accurate timing due all the stuff
going on the back ground. Four or five  Hall effect
sensors per rotor 10 degrees apart are the hot tip.
One rotating magnet is all you need.

This is a homebuilt MSD system with one spark
every 10 degrees starting at 20 degrees BTDC.
400 watts ought to be plenty. No guarantee on
spark plug life however. Try iridium.

I need to update 555 crank angle sensor 3 dwg to show
more HE sensors.

Paul Lamar