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



I like digital stuff as much as anyone..  However, have you considered
something as simple as a winding and wiper variable resistance
approach similar to a fuel level sensor?  I believe it would be
relatively simple to build, very compact, low parts count, and
lightweight.  It would be the same technology used in existing
throttle position sensors.  It could probably use parts from a float
sensor.

Another idea would be to make a variable capacitance sensor (also
similar to a fuel level sensor)..  A tube and an insulated rod.
Actuation of the throttle would change the amount rod inserted in the
tube, changing the capacitance between them.  Use the capacitance in
an oscillating circuit, and detect the change in frequency.


Cheers,

Matt-

That would require a analog to digital converter.
With this device all you need is a couple of RS232 ports and
one bidirectional parallel port. I say bidirectional as all printer
ports are not bidirectional. One can get a PCI extender card if
the small PC mother board has only one PCI slot. Most do.

BTW I decided to add  another e-shaft trigger for the second
rotor as that greatly simplifies the software and cuts the software
execution time greatly. No figuring out mathematically when to fire
the second rotor. It is just another hardware interrupt.

The great thing about RS232 is they will accept a raw 12 volt pulse
from the CAS directly on the RXD line pin 2. No nada. Anyway I think.
I have not tested it so far but I am about to.

The DOS-QB command is ON COM(x) GOSUB DealWithR2

Thats it!!! That is the hardware interrupt.

On the advanced level one RES232 port could in theory
handle as many as 8 hardware interrupts as there are
at least 3 input limes. A CMOS 4532 priority encoder running
on 12 vbolts could drive those 3 bits telling the program
which of 8 interrupts occurred. One does this by PEEK ing
the RS232 input ports directly. I first used this trick
about 1975 :)

Paul Lamar