Re: Help with DRO

>
> From: Joe Vicars <jvicars@...>
>
> I have a picture of a servo encoder that was broken and I removed it
> from it's motor. Can someone tell me which wires do what? I have 6
> more of these encoders (unbroken) that I would like to use for DRO.
> If you think you can help I will email you a Word document with the
> pictures in it. I will also include the wiring schematic for Lindsay's
> DRO.
> Help is appreciated.

What Joe has are quadrature decoders, with glass disks.

There is no magic answer to your question, but I think this should
give you enough info to figure your exact wiring diagram out.

First off, I'd test on your broken unit.

I don't know how much you know wabout how these encoders work, so I'll
be extra descriptive, you could also look on the web.
the robotics guys use these, and there are some good tutorials
out there.

Your picture shows the lower housing, the wheel, and 6 wires.
There are red, orange, black & brown going to the lower housing.
There are green & black wires going to a removed part.
That part is an LED. IT may very well be Infrared, if so you
won't be able so see that it is on.

The short description is this:
That LED shines light thru slots or holes, thru the disk, and is
picked up by the sensors in the bottom housing.

The sensors are spaced so that when one is dead center over a black
line on the glass, the other one is at an edge.

As you rotate the wheel, the light will shine thru or be blocked
as each line passes by the sensors.

You will get a signal, for now we will assume positive logic, so
the signal will be 5 volts.

It would look like this:

5V ---- ---- ---- ---- ---- ----
| | | | | | | | | | | | chanel A
0V -- ---- ---- ---- ---- ----
5V---- ---- ---- ---- ---- ----
| | | | | | | | | | | | chanel A
0V- ---- ---- ---- ---- ---- --

By watching the order the signals change, and by counting the
number of changes, you can determine which direction the wheel is
turning, and how far it has moved.

judging from the picture, I say the next step would be to trace
the 4 remaining wires, break it open if necesary.

The green and black wires run the light source, you will need to
determine the correct polarity. from looking at the tab on the
case of the LED, I bet the black is ground and the green is
positive. @ 5V, these will probablt need a limiting resistor, to
prevent them from burning up, how big, and how to determine that
is a whole post in and of itself.

presuming the bottom housing comes apart like the top, and the
sensors are wired the same way it should be easy to figure the
rest of the connections out.

If I were to guess, the wires go to photo-transistors.
they will look similar to the part you have out, but may have
3 leads.

There may be 2 or 3, they MAY also be combined into one sensor,
although I've never seen it.

If there are 3 one is probably an index pulse, this gives you
a known location on the shaft to start from if the actual
rotation from a given point is of interest.

I'd go get some LEDs, to practice, and test this, once you
think you have it figured out.

when it is wired correctly, you should be able to connect the
wires the diagram shows going to the parallel port pins 2 & 3
to a couple of LEDs with resistors, and see them alternately
turn on and off as the shaft is rotated.