OT, but kinda on topic - optical encoder elex
 

I found a small DC motor at the dump with an optical encoder on it. I'd
like to be able to use it, but I have no specs on the encoder. It's a
Rae Corp motor, but the sticker is stamped "Aug 27 1976", so I have no
hope of finding specs for it.

There are 2 micro ckt bds, but glued in place so ckt tracing is out. I
can see 2 emitter/sensor pairs & there are 4 wires. My best guess is
that the ckt looks like this:


Blk Y Blue
| | |
+-+--+ | |
| | | |
+++ +++ +++ +++ Photo
LEDs | | | | | | | | Detectors
| | | | | | | |
+++ +++ +++ +++
| | | |
|____|_________|_____|
|
|
|
R

(based upon using a VOM & seeing that Y-Blue = Y-R + R-Blue). The LED
pair is 600k in 1 direction & 1.8M in the other. The detectors are
about 2k in both directions. There are also 4 resistors: 2 fixed & 2
trim. Does this make sense? In particular, does it make sense that the
detectors would have the same resistance in both directions?

Then, how would I hook it up?
- voltage to apply to Blk (LEDs)?
- a resistor on each of Y & Blue in series to voltage, signal taken at Y
& Blue?
- if so, voltage & resistance values?

Thanks,
Bob

--
Nota for President

OT, but kinda on topic - optical encoder elex
 

Bob Engelhardt wrote:
I found a small DC motor at the dump with an optical encoder on it. I'd
like to be able to use it, but I have no specs on the encoder. It's a
Rae Corp motor, but the sticker is stamped "Aug 27 1976", so I have no
hope of finding specs for it.

There are 2 micro ckt bds, but glued in place so ckt tracing is out. I
can see 2 emitter/sensor pairs & there are 4 wires. My best guess is
that the ckt looks like this:


Blk Y Blue
| | |
+-+--+ | |
| | | |
+++ +++ +++ +++ Photo
LEDs | | | | | | | | Detectors
| | | | | | | |
+++ +++ +++ +++
| | | |
|____|_________|_____|
|
|
|
R

(based upon using a VOM & seeing that Y-Blue = Y-R + R-Blue). The LED
pair is 600k in 1 direction & 1.8M in the other. The detectors are
about 2k in both directions. There are also 4 resistors: 2 fixed & 2
trim. Does this make sense? In particular, does it make sense that the
detectors would have the same resistance in both directions?

Then, how would I hook it up?
- voltage to apply to Blk (LEDs)?
- a resistor on each of Y & Blue in series to voltage, signal taken at Y
& Blue?
- if so, voltage & resistance values?

Thanks,
Bob

It is quite odd that the detectors should be 2K in both directions,
unless the circuit is designed to have a supply voltage connected
between red & black, and let you pick signal off of yellow and blue
without needing any pullup resistors.

Which direction do the LEDs read low? From the color code I would
assume that red is +5V and black is ground, but black & red aren't
always - and +.

I'd hook up black & red in the direction that seems favored for current
to flow through the LEDs, through a current limiting resistor, and see
if I could get it up to no more than 50mA at 5V. That's high enough to
damage something, and I'd be cautious, but I'll be damned if I can
describe it step by step -- "looks like a forward biased LED" is what
I'd look for. Once there, I'd see if there's output on the yellow and blue.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

OT, but kinda on topic - optical encoder elex
 

Tim Wescott wrote:
Bob Engelhardt wrote:
...


Blk Y Blue
| | |
+-+--+ | |
| | | |
+++ +++ +++ +++ Photo
LEDs | | | | | | | | Detectors
| | | | | | | |
+++ +++ +++ +++
| | | |
|____|_________|_____|
|
|
|
R
....


It is quite odd that the detectors should be 2K in both directions,
unless the circuit is designed to have a supply voltage connected
between red & black, and let you pick signal off of yellow and blue
without needing any pullup resistors.


That occurred to me right after I sent it. I.e., that there are
built-in pull ups & yellow & blue are read directly. That doesn't
explain to me why the resistance would be the same - unless the pull up
resistor is the back resistance of the detector.

...

I'd hook up black & red in the direction that seems favored for current
to flow through the LEDs, through a current limiting resistor, and see
if I could get it up to no more than 50mA at 5V. ...
... I'd see if there's output on the yellow and blue.


I did & there is. There must be a limiting resistor in there, 'cause I
forgot it & it followed the applied voltage, kinda. At about 5v (red
+), the emitters draw 30 ma & I get about .7v on yellow & blue. Not a
square wave, as I expected it would be. More sinusoidal than anything.

The 4 resistors that are there must be 2 current limiting on the LEDs
and 2 pull ups on the detectors. Wait - this was made in 1976: did they
have LEDs then?

Thanks for your help,
Bob

--
Nota for President

OT, but kinda on topic - optical encoder elex
 

On Tue, 09 Sep 2008 17:50:35 -0400, Bob Engelhardt wrote:


The 4 resistors that are there must be 2 current limiting on the LEDs
and 2 pull ups on the detectors. Wait - this was made in 1976: did they
have LEDs then?


Yes. Commercial red LEDs were avialble in the 60's; I think by the 70's
they were on to other colours and higher output levels.

OT, but kinda on topic - optical encoder elex
 

Fairchild Semi Optical was in full swing.

My former - through my sister - uncle-in-law (I suppose) was the
executive VP of Semi and had that operation to himself.

I suspect you have a servo with sensing.

Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


_ wrote:
On Tue, 09 Sep 2008 17:50:35 -0400, Bob Engelhardt wrote:


The 4 resistors that are there must be 2 current limiting on the LEDs
and 2 pull ups on the detectors. Wait - this was made in 1976: did they
have LEDs then?


Yes. Commercial red LEDs were avialble in the 60's; I think by the 70's
they were on to other colours and higher output levels.


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OT, but kinda on topic - optical encoder elex
 

On 2008-09-09, Bob Engelhardt wrote:
I found a small DC motor at the dump with an optical encoder on it. I'd
like to be able to use it, but I have no specs on the encoder. It's a
Rae Corp motor, but the sticker is stamped "Aug 27 1976", so I have no
hope of finding specs for it.

There are 2 micro ckt bds, but glued in place so ckt tracing is out. I
can see 2 emitter/sensor pairs & there are 4 wires. My best guess is
that the ckt looks like this:


Blk Y Blue
| | |
+-+--+ | |
| | | |
+++ +++ +++ +++ Photo
LEDs | | | | | | | | Detectors
| | | | | | | |
+++ +++ +++ +++
| | | |
|____|_________|_____|
|
|
|
R

(based upon using a VOM & seeing that Y-Blue = Y-R + R-Blue). The LED
pair is 600k in 1 direction & 1.8M in the other. The detectors are
about 2k in both directions. There are also 4 resistors: 2 fixed & 2
trim. Does this make sense? In particular, does it make sense that the
detectors would have the same resistance in both directions?

Hmm ... the detectors could be photo-resistive -- which would
mean that they are fairly slow response. Or it could be two detectors
in parallel -- one facing each way, so you could connect either way
around.

Then, how would I hook it up?

How *I* would try it:

BLK to ground
RED to +5V

Yellow and Blue to transistor base connections -- perhaps with a
series resistor to limit the maximum current through the base-emitter
junctions to something reasonable. (There may be one built in to each,
but until you are sure, it is safer to protect it.)

1976 could be designed to drive TTL or CMOS, but most TTL would
not want the pull-up current which your sketched design would give it.

BTW The two LEDs could be in series instead of in parallel, since
5V is more than you need to drive one LED.

The LEDs may be visible (red) or may be IR LEDs. You can try
applying the +5V to red and the GND to black and see whether it is
visible in low light levels. If you have an older digital camera, you
can probably detect IR with it -- and let its screen display a visible
light color for you.

- voltage to apply to Blk (LEDs)?

Common color code is BLACK for ground, and RED for +5V. It is
unlikely that you will have a lower voltage required on that old a
device, assuming that there are resistors in series with the LEDs.

- a resistor on each of Y & Blue in series to voltage, signal taken at Y
& Blue?

A resistor on each to ground (BLACK), with signal taken at Y and
Blue.

- if so, voltage & resistance values?

Voltage -- 5V DC.

Resistance (for starters) of perhaps 4.7 K Ohms to check things
out with a voltmeter or a 'scope.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

OT, but kinda on topic - optical encoder elex
 

Bob Engelhardt wrote:
Tim Wescott wrote:
Bob Engelhardt wrote:
...


Blk Y Blue
| | |
+-+--+ | |
| | | |
+++ +++ +++ +++ Photo
LEDs | | | | | | | | Detectors
| | | | | | | |
+++ +++ +++ +++
| | | |
|____|_________|_____|
|
|
|
R
...


It is quite odd that the detectors should be 2K in both directions,
unless the circuit is designed to have a supply voltage connected
between red & black, and let you pick signal off of yellow and blue
without needing any pullup resistors.


That occurred to me right after I sent it. I.e., that there are
built-in pull ups & yellow & blue are read directly. That doesn't
explain to me why the resistance would be the same - unless the pull up
resistor is the back resistance of the detector.

...
I'd hook up black & red in the direction that seems favored for
current to flow through the LEDs, through a current limiting resistor,
and see if I could get it up to no more than 50mA at 5V. ...
... I'd see if there's output on the yellow and blue.


I did & there is. There must be a limiting resistor in there, 'cause I
forgot it & it followed the applied voltage, kinda. At about 5v (red
+), the emitters draw 30 ma & I get about .7v on yellow & blue. Not a
square wave, as I expected it would be. More sinusoidal than anything.

A chopper wheel will give you a trapazoidal to outright triangular
output waveform, because the transitions on the wheel wipe across the
sensor in a noticeable amount of time. I worked on a motion control
system where we used the analog edges to provide a fractional part of an
encoder count. It was kind of hairy to implement in assembly language,
but it worked well. We got about 6 extra bits of resolution for the effort.

The 4 resistors that are there must be 2 current limiting on the LEDs
and 2 pull ups on the detectors. Wait - this was made in 1976: did they
have LEDs then?


As a wild guess, could those sensors be Cadmium Sulfide sensors? I
always thought that they would be too slow for this task, but I believe
that they are effectively photo-resistive and not polarity sensitive.
All of the CdS cells I have seen have a good sized window on them and
and a noticeable squiggly line dividing the sensor in half.

Curious,
BobH

OT, but kinda on topic - optical encoder elex
 

I was looking at my 1976 Linear data book - and recalled that I built a
7 segment LED clock for my beloved in '77. And I just pulled out my
1975 TI Optoelectronics Data book I bought for $2.95.

So that was likely a class part 40 years ago.

Martin

Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


Martin H. Eastburn wrote:
Fairchild Semi Optical was in full swing.

My former - through my sister - uncle-in-law (I suppose) was the
executive VP of Semi and had that operation to himself.

I suspect you have a servo with sensing.

Martin
Martin H. Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
TSRA, Endowed; NRA LOH & Patron Member, Golden Eagle, Patriot's Medal.
NRA Second Amendment Task Force Charter Founder
IHMSA and NRA Metallic Silhouette maker & member.
http://lufkinced.com/


_ wrote:
On Tue, 09 Sep 2008 17:50:35 -0400, Bob Engelhardt wrote:


The 4 resistors that are there must be 2 current limiting on the LEDs
and 2 pull ups on the detectors. Wait - this was made in 1976: did
they have LEDs then?


Yes. Commercial red LEDs were avialble in the 60's; I think by the 70's
they were on to other colours and higher output levels.


----== Posted via Pronews.Com - Unlimited-Unrestricted-Secure Usenet
News==----
http://www.pronews.com The #1 Newsgroup Service in the World! 100,000
Newsgroups
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---= - Total Privacy via Encryption =---

OT, but kinda on topic - optical encoder elex
 

On Sep 9, 2:40 pm, Bob Engelhardt wrote:
I found a small DC motor at the dump with an optical encoder on it. I'd
like to be able to use it, but I have no specs on the encoder....

Bob

An ohmmeter doesn't tell you enough about active devices. You get much
more useful information from a curve trace, which is easy to do with
two meters, a power supply and some current-limiting resistors or
pots. Push measured currents through the circuit and record the
voltage drop. 10V and 10mA max should be safe for most transistors and
diodes but don't let it feed through to TTL chips. I bought four of
the $4 - $5 digital meters from Harbor Freight for this type of
setup.

The LEDs should drop about 1.5V - 2V at 10mA unless they have internal
limiting resistors. Other diodes and transistor base-emitter junctions
drop 0.5V - 0.7V at currents from 100uA to 10mA. For resistors the
drop is proportional to the current while diode drop is logarithmic.
If you have both in series, make a plot of voltage and current and
draw a line through the points. The slope of the line gives
resistance, the voltage at zero current is the diode. Reverse-biased
base-emitter junctions may break down like a sloppy Zener diode at
around 6V.

Jim Wilkins

OT, but kinda on topic - optical encoder elex
 

BobH wrote:
....
As a wild guess, could those sensors be Cadmium Sulfide sensors? I
always thought that they would be too slow for this task, but I believe
that they are effectively photo-resistive and not polarity sensitive.
All of the CdS cells I have seen have a good sized window on them and
and a noticeable squiggly line dividing the sensor in half.

Ah, I can't see them - they're buried in an assembly with just a slit
for the wheel. Bob

--
Nota for President

OT, but kinda on topic - optical encoder elex
 

On Sep 9, 4:38*pm, Tim Wescott wrote:
Bob Engelhardt wrote:
It is quite odd that the detectors should be 2K in both directions,
....
Tim Wescott

Unless the resistor is in parallel with the photo detector?

OT, but kinda on topic - optical encoder elex
 

Jim Wilkins wrote:
An ohmmeter doesn't tell you enough about active devices. You get much
more useful information from a curve trace, which is easy to do with
two meters, a power supply and some current-limiting resistors or
pots. Push measured currents through the circuit and record the
voltage drop. 10V and 10mA max should be safe for most transistors and
diodes but don't let it feed through to TTL chips. ...

The LEDs should drop about 1.5V - 2V at 10mA unless they have internal
limiting resistors. Other diodes and transistor base-emitter junctions
drop 0.5V - 0.7V at currents from 100uA to 10mA. For resistors the
drop is proportional to the current while diode drop is logarithmic.
If you have both in series, make a plot of voltage and current and
draw a line through the points. The slope of the line gives
resistance, the voltage at zero current is the diode. Reverse-biased
base-emitter junctions may break down like a sloppy Zener diode at
around 6V.

Jim Wilkins

Good stuff! I'll file it for future use. Meaning for now I'm just
going to hook up the 5v & run the detector outputs into some high
impedance something & let it be a black box. That is, when I get around
to it G.

Thanks,
Bob

--
Nota for President