This is an array of standard .2 inch diameter infrared
 photo transistors and LEDs.  There is a slot in the slide
 that allows the light to travel from one LED to its corresponding
 photo transistor. Very simple and straight forward. These parts
 are about 80 cents each.  This gives slide throttle position
 to one part in 16 or 1/8th of an inch. Two $2 chips called a
 8 bit priority encoders are used to out put  a 4 bit
 (1 part in 16) binary number to a parallel input port.

 The advantage of this approach is you know
 where the throttle is and you know if it has moved quickly
 so an enrichment pulse can be sent to the injectors to
 prevent stumble. It is possible one could do away with
 the manifold pressure sensor and just use this information
 along with RPM to adjust the mixture.

 This is a piece of cake for a DOS-QB EFI system.
 The parallel port is read by one statement called
 a PEEK in QB. QB can tell how fast the throttle
 is moving by recording the last time it was moved
 and subtracting that time from the next time it moves.
 If it is less than a .1 second than somebody jammed
 the throttle open :)

 Paul Lamar

 Paul.

 O.2 inch is about 5mm.  I have seen 3mm ones and their might be smaller
 ones available.  You could also accomplish the same thing  with one
 optical reader like my torque sensor idea.  Have it read dots, or
 patterns that correspond to binary numbers.

 Doug in Japan

 I was just going on what DigiKey was offering. It would be nice if they
 were smaller. I could not find any. Got any data on your optical reader?
 I have had problems with optical readers in the past and I have
 found the interrupter design to be more reliable. The one side optical
 readers is sensitive to ambient light level. The other advantage to this
 approach is the current slide throttle covers provide the package and
 holders for LEDs, photo transistors and the PC boards. No device needs
 to be mounted or attached to the throttle cable. I might offer a kit
 way down the road if enough people are interested in the PC DOS-QB EFI.
 It can be retrofitted to current slide throttles that are out there.

 Paul Lamar


 How about this:

 4 photo diodes, 4 LED's.  Mount them in a single line perpendicular to
 the axis of the slide.  Binary encode the position by drilling lines
 of grey code holes across the array.  Grey code so that transitioning
 from one position to the next only changes one bit of the code -
 eliminating spurious glitching.  As the slide moves, a different count
 is made present across the photo diodes - no other encoding required.
 At one end of the slide, only one hole, at the other end of the slide,
 4 holes (16 counts).

 To deal with radiation contamination (that's DC offset/drift), the
 emitters (LED's) should be modulated at something like 20kHtz, and the
 photo diodes should have a simple high pass filter driving a follower
 (buffer) driving a rectifier and low pass filter, driving a
 comparator.  Have to look at the datasheets to see the response curves
 to pick a good frequency.  It might be helpful to turn on only one
 emitter at a time and read only that emitter's photo diode at that
 time - to reduce the chance of contamination from one to the next.
 The computer can easily switch between them fast enough to not miss
 any movement.


 Matt-

 Draw it up Matt. I would like to look at it.
 If there is any width to the place where the holes go that could
 interfere with blocking the intake ports. I explored that and gave up
 on it for that reason. I drew it out to scale.  The current scheme
 needs only one narrow slot in the slide.

 Paul Lamar


 Why not just build it up as a unit separate from the slide throttle and
 place it in the cockpit and mechanically connect it to the throttle cable?

 Joe Berki

 More work. More time.

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

 OK I found some smaller transistors. This reduced the
 area needed on the slide throttle.

 Here is a pdf on the transistors and a few 3Ds of the
 slide throttle position sensor.

 I can use the MTIME function in PB to tell when somebody has slammed
 the throttle open.

 Paul Lamar


  Paul,

  My drawing skills are quite rusty, but attached is a picture with the
  basic idea..  The slots are the additional openings that would be
  added to the existing throttle plate.  The round objects are the holes
  that would be added to the existing throttle housing - sensors in
  holes on on one side, LED's on the other.

  The slots could/should be narrower.

  And the sensors/slots don't have to be right next to each other..
  They could be arrayed along the top of the throttle plate, one sensor
  for each series of slots.  Just so long as the corresponding
  sensor/LED and slot are moved together.


  Matt-

  Yes I see what your doing now. That will work. IMHO it has two drawbacks.
  It needs to be done in a mill and it won't fit between the tubes with
  out leaking air when the slide is wide open. It must be two inches
  long so one would have to increase the length of the slide by one or
  2 inches or so to fit it between the aft tube and the throttle cable.
  I would like to be able to retrofit to current slide throttles.
  The old scheme can be done in a drill press.

  Paul Lamar


  Concur on the need for milling.  However, I believe my approach can be
  applied to existing parts.   If the slide movement is two inches, and
  the length is eight inches, there's room for four evenly spaced
  sensors arranged in series along the top edge of the slide.

 Each of
  the sensors will see the same slots as depicted in my drawing - just
  arranged in series instead of parallel.


  Matt-


 One other comment: The slots (or for your case, round holes) can be
 much smaller than the diameter of the LED's or sensors - preserving
 material for sealing and strength.


 Matt-


Oh wait..  The holes on yours may need to be nearly as large as the
sensor/LED because yours depends on not having any place where no
sensor is lit..  If you had small holes, I think there would end up
being blank spots between where LED lines up with sensor.

Matt-

True the limitation is the diameter of the photo tx.
I found some that were only .116 in diameter instead of .2.
Also the gray code would be a problem for me.
Mors software over head.

Paul Lamar