I bought a Trav-A-Dial from a fellow poster here. It's one of the ones
with a built in encoder. Southwestern Industries can't or won't tell
you what signals it outputs or what voltage it uses. With help from US
Digital and from Ned Simmons telling me how to use an oscilloscope to
watch the encoder working and google I have been successful in
figuring out how to hook up one of these. The operate from 5 volts. On
the unit I have the black wire is +5 volts and the white wire is GND.
The red and yelow wires are one pair of Nand and And outputs and the
violet and green wires are the other pair. The encoder disc has 250
lines on it. Using a digital readout from US Digital, #ED3, configured
to read in quadrature, will give the Trav-a-Dial .0001" resolution.
From the ED# connect the +5 volts to black, GND to white, channel A
to red and channel B to violet. Configure ithe ED3 so that one count
equals .0001 and that it counts in quadrature. You will now have a
..0001" resolution digital display from your Trav-A-Dial.
ERS

I don't have much interest in Travadial, but that sounds like
a GREAT hacking job you've done there. Congratulations!

DOC


"Eric R Snow" wrote in message
...
I bought a Trav-A-Dial from a fellow poster here. It's one of the ones
with a built in encoder. Southwestern Industries can't or won't tell
you what signals it outputs or what voltage it uses. With help from US
Digital and from Ned Simmons telling me how to use an oscilloscope to
watch the encoder working and google I have been successful in
figuring out how to hook up one of these. The operate from 5 volts. On
the unit I have the black wire is +5 volts and the white wire is GND.
The red and yelow wires are one pair of Nand and And outputs and the
violet and green wires are the other pair. The encoder disc has 250
lines on it. Using a digital readout from US Digital, #ED3, configured
to read in quadrature, will give the Trav-a-Dial .0001" resolution.
From the ED# connect the +5 volts to black, GND to white, channel A
to red and channel B to violet. Configure ithe ED3 so that one count
equals .0001 and that it counts in quadrature. You will now have a
.0001" resolution digital display from your Trav-A-Dial.
ERS

Eric,
Did you ever resolve the encoder problem you were fighting with a few
weeks ago? If yes, what did it work out to be? Sorry if I missed it at
the bottom of one of the threads.

Bob

On Sun, 30 Oct 2005 15:38:06 GMT, MetalHead
wrote:

Eric,
Did you ever resolve the encoder problem you were fighting with a few
weeks ago? If yes, what did it work out to be? Sorry if I missed it at
the bottom of one of the threads.

Bob
Bob,
I'm still working on it. I have made a new pulley with a thread cut
into it for the cable to wrap around. I have also made a mirror holder
for the laser. But some other more important things had to be done
first and I won't be able to get back to it until next week. But I
will post the results.
Eric

Eric R Snow wrote:
On Sun, 30 Oct 2005 15:38:06 GMT, MetalHead
wrote:


Eric,
Did you ever resolve the encoder problem you were fighting with a few
weeks ago? If yes, what did it work out to be? Sorry if I missed it at
the bottom of one of the threads.

Bob

Bob,
I'm still working on it. I have made a new pulley with a thread cut
into it for the cable to wrap around. I have also made a mirror holder
for the laser. But some other more important things had to be done
first and I won't be able to get back to it until next week. But I
will post the results.
Eric

Thanks Eric, I am curious about that one.

Bob

On Sun, 30 Oct 2005 19:23:31 GMT, MetalHead
wrote:

Eric R Snow wrote:
On Sun, 30 Oct 2005 15:38:06 GMT, MetalHead
wrote:


Eric,
Did you ever resolve the encoder problem you were fighting with a few
weeks ago? If yes, what did it work out to be? Sorry if I missed it at
the bottom of one of the threads.

Bob

Bob,
I'm still working on it. I have made a new pulley with a thread cut
into it for the cable to wrap around. I have also made a mirror holder
for the laser. But some other more important things had to be done
first and I won't be able to get back to it until next week. But I
will post the results.
Eric

Thanks Eric, I am curious about that one.

Bob
Bob,
One of the things I'm not sure about is how to determine the length of
an unwrapped helix. If the radius and pitch are known then that should
be enough info to calculate the length exactly but I haven't been
satisfied with the answers I have come up with. Do you know how to do
this? I think that if a right triangle is wrapped around a cylinder
then the hypotenuse would be the length of the unwound helix. Do you
know if this is correct?
Eric

Eric R Snow wrote:
On Sun, 30 Oct 2005 19:23:31 GMT, MetalHead
wrote:


Eric R Snow wrote:

On Sun, 30 Oct 2005 15:38:06 GMT, MetalHead
wrote:



Eric,
Did you ever resolve the encoder problem you were fighting with a few
weeks ago? If yes, what did it work out to be? Sorry if I missed it at
the bottom of one of the threads.

Bob

Bob,
I'm still working on it. I have made a new pulley with a thread cut
into it for the cable to wrap around. I have also made a mirror holder
for the laser. But some other more important things had to be done
first and I won't be able to get back to it until next week. But I
will post the results.
Eric

Thanks Eric, I am curious about that one.

Bob

Bob,
One of the things I'm not sure about is how to determine the length of
an unwrapped helix. If the radius and pitch are known then that should
be enough info to calculate the length exactly but I haven't been
satisfied with the answers I have come up with. Do you know how to do
this? I think that if a right triangle is wrapped around a cylinder
then the hypotenuse would be the length of the unwound helix. Do you
know if this is correct?
Eric

My college Calc book says that is correct:

for a cylinder of radius A, with a pitch of C, the arc length will be
2 * pi * sqrt(A^2 + C^2)

If you weren't trying for tenths of a mil, I would say ignore the pitch
contribution. As it is, probably not. Two other contributers that I
don't know the answer to a cable diameter and wrapping accuracy.

Do you calculate the radius of the pulley at the surface of the pulley,
the center of the cable or the outside of the pulley plus the cable?

Wrapping accuracy, does that cable really lay down on the pulley
repeatably enough? What kind of tension is required to get that
assumption to be valid?

There have been a number of times that I wish I had gone for an
Mechanical Engineering degree instead of a Computer Engineering one. As
it is, this would be an experimentation project for me. Sorry I can't
give you a better answer on that one.

Bob