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Posted by Mr. INTJ on August 17, 2008, 6:48 am
Hi,
I'm a software guy groping around in EE-land, and I could use a little
help.
A few old inkjet printers yielded up some nice motors with optical
rotary encoders built in. There are only six wires coming from the
connector on the back of the motor/encoder. Two of the wires go
directly to the DC motor. The other four are for the I-R emitter and
the two I-R detectors. Here are some lovely photos, in case they help:
http://www.minsmithphoto.com/mrintj/encoder-top.jpg
http://www.minsmithphoto.com/mrintj/encoder-back.jpg
http://www.minsmithphoto.com/mrintj/encoder-bottom.jpg
Using a low-voltage diode tester, and squinting at the traces on the
circuit board, I came up with the following circuit diagram...
http://www.minsmithphoto.com/mrintj/schematic.png
I've powered up the emitter, put an ohmmeter on one of the photodiodes
(in forward polarity), and watched the resistance go from high to low
as I slowly turn the motor shaft.
Even though it seems to work, I can't help but feel that something is
wrong. I would have expected the two photodiodes to share a common
anode or cathode, but that doesn't seem to be the case. Also, I'm
puzzled as to why they would be connected in the direction that they
are - so that I'd need a supply greater than +5V to read D1 and a
negative supply to read D3?
Surely, I've made a mistake somewhere, but when I go back through the
process of measuring and visual inspection, I end up with the same
goofy schematic.
What am I doing wrong? I'm assuming that the detectors (on the bottom
of the opto-interrupter assembly, closest to the circuit board) *are*
two individual photo diodes. An EE at work suggested that they may be
ICs with built-in amplifiers, etc...
Can anyone shed some light on this?
Thanks.
Mr. INTJ
San Diego, CA
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Posted by BobH on August 17, 2008, 9:33 am
Mr. INTJ wrote:
> Hi,
>
> I'm a software guy groping around in EE-land, and I could use a little
> help.
>
> A few old inkjet printers yielded up some nice motors with optical
> rotary encoders built in. There are only six wires coming from the
> connector on the back of the motor/encoder. Two of the wires go
> directly to the DC motor. The other four are for the I-R emitter and
> the two I-R detectors. Here are some lovely photos, in case they help:
>
> http://www.minsmithphoto.com/mrintj/encoder-top.jpg
> http://www.minsmithphoto.com/mrintj/encoder-back.jpg
> http://www.minsmithphoto.com/mrintj/encoder-bottom.jpg
>
> Using a low-voltage diode tester, and squinting at the traces on the
> circuit board, I came up with the following circuit diagram...
>
> http://www.minsmithphoto.com/mrintj/schematic.png
>
> I've powered up the emitter, put an ohmmeter on one of the photodiodes
> (in forward polarity), and watched the resistance go from high to low
> as I slowly turn the motor shaft.
>
> Even though it seems to work, I can't help but feel that something is
> wrong. I would have expected the two photodiodes to share a common
> anode or cathode, but that doesn't seem to be the case. Also, I'm
> puzzled as to why they would be connected in the direction that they
> are - so that I'd need a supply greater than +5V to read D1 and a
> negative supply to read D3?
>
> Surely, I've made a mistake somewhere, but when I go back through the
> process of measuring and visual inspection, I end up with the same
> goofy schematic.
>
> What am I doing wrong? I'm assuming that the detectors (on the bottom
> of the opto-interrupter assembly, closest to the circuit board) *are*
> two individual photo diodes. An EE at work suggested that they may be
> ICs with built-in amplifiers, etc...
>
What manufacturer printer did they come out of? Are the motors from the
paper path or the carriage?
Are there any part numbers on the sensor?
I am only familiar with the HP ones, but they did have an internal amp.
Those parts had 4 terminals: +5V, Ground and two phase output signals.
Some of them had logic level phase outputs and some of them had current
mode analog outputs. HP's Opto manufacturing group got renamed to
Agilent when the spinoff happened and then recently to Avago.
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Posted by Mr. INTJ on August 18, 2008, 2:03 am
wrote:
> Mr. INTJ wrote:
> > Hi,
> > I'm a software guy groping around in EE-land, and I could use a little
> > help.
> > A few old inkjet printers yielded up some nice motors with optical
> > rotary encoders built in. There are only six wires coming from the
> > connector on the back of the motor/encoder. Two of the wires go
> > directly to the DC motor. The other four are for the I-R emitter and
> > the two I-R detectors. Here are some lovely photos, in case they help:
> >http://www.minsmithphoto.com/mrintj/encoder-top.jpg
> >http://www.minsmithphoto.com/mrintj/encoder-back.jpg
> >http://www.minsmithphoto.com/mrintj/encoder-bottom.jpg
> > Using a low-voltage diode tester, and squinting at the traces on the
> > circuit board, I came up with the following circuit diagram...
> >http://www.minsmithphoto.com/mrintj/schematic.png
> > I've powered up the emitter, put an ohmmeter on one of the photodiodes
> > (in forward polarity), and watched the resistance go from high to low
> > as I slowly turn the motor shaft.
> > Even though it seems to work, I can't help but feel that something is
> > wrong. I would have expected the two photodiodes to share a common
> > anode or cathode, but that doesn't seem to be the case. Also, I'm
> > puzzled as to why they would be connected in the direction that they
> > are - so that I'd need a supply greater than +5V to read D1 and a
> > negative supply to read D3?
> > Surely, I've made a mistake somewhere, but when I go back through the
> > process of measuring and visual inspection, I end up with the same
> > goofy schematic.
> > What am I doing wrong? I'm assuming that the detectors (on the bottom
> > of the opto-interrupter assembly, closest to the circuit board) *are*
> > two individual photo diodes. An EE at work suggested that they may be
> > ICs with built-in amplifiers, etc...
> What manufacturer printer did they come out of? Are the motors from the
> paper path or the carriage?
> Are there any part numbers on the sensor?
> I am only familiar with the HP ones, but they did have an internal amp.
> Those parts had 4 terminals: +5V, Ground and two phase output signals.
> Some of them had logic level phase outputs and some of them had current
> mode analog outputs. HP's Opto manufacturing group got renamed to
> Agilent when the spinoff happened and then recently to Avago.
These are from HP inkjet printers. You were right about the logic
levels - I just hooked both phase outputs up to individual traces on
my scope, and there they are - textbook logic signals, with a phase
difference according to direction. My mistake seems to have been
assuming that these were individual photo diodes. :-(
Thanks!
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Posted by BobH on August 19, 2008, 12:21 am
Mr. INTJ wrote:
> wrote:
>> Mr. INTJ wrote:
>>> Hi,
>>> I'm a software guy groping around in EE-land, and I could use a little
>>> help.
>>> A few old inkjet printers yielded up some nice motors with optical
>>> rotary encoders built in. There are only six wires coming from the
>>> connector on the back of the motor/encoder. Two of the wires go
>>> directly to the DC motor. The other four are for the I-R emitter and
>>> the two I-R detectors. Here are some lovely photos, in case they help:
>>> http://www.minsmithphoto.com/mrintj/encoder-top.jpg
>>> http://www.minsmithphoto.com/mrintj/encoder-back.jpg
>>> http://www.minsmithphoto.com/mrintj/encoder-bottom.jpg
>>> Using a low-voltage diode tester, and squinting at the traces on the
>>> circuit board, I came up with the following circuit diagram...
>>> http://www.minsmithphoto.com/mrintj/schematic.png
>>> I've powered up the emitter, put an ohmmeter on one of the photodiodes
>>> (in forward polarity), and watched the resistance go from high to low
>>> as I slowly turn the motor shaft.
>>> Even though it seems to work, I can't help but feel that something is
>>> wrong. I would have expected the two photodiodes to share a common
>>> anode or cathode, but that doesn't seem to be the case. Also, I'm
>>> puzzled as to why they would be connected in the direction that they
>>> are - so that I'd need a supply greater than +5V to read D1 and a
>>> negative supply to read D3?
>>> Surely, I've made a mistake somewhere, but when I go back through the
>>> process of measuring and visual inspection, I end up with the same
>>> goofy schematic.
>>> What am I doing wrong? I'm assuming that the detectors (on the bottom
>>> of the opto-interrupter assembly, closest to the circuit board) *are*
>>> two individual photo diodes. An EE at work suggested that they may be
>>> ICs with built-in amplifiers, etc...
>> What manufacturer printer did they come out of? Are the motors from the
>> paper path or the carriage?
>> Are there any part numbers on the sensor?
>> I am only familiar with the HP ones, but they did have an internal amp.
>> Those parts had 4 terminals: +5V, Ground and two phase output signals.
>> Some of them had logic level phase outputs and some of them had current
>> mode analog outputs. HP's Opto manufacturing group got renamed to
>> Agilent when the spinoff happened and then recently to Avago.
>
> These are from HP inkjet printers. You were right about the logic
> levels - I just hooked both phase outputs up to individual traces on
> my scope, and there they are - textbook logic signals, with a phase
> difference according to direction. My mistake seems to have been
> assuming that these were individual photo diodes. :-(
>
> Thanks!
Sure, glad to help.
Photo diodes would only be used in very high speed applications I think.
Normal low cost opto-interrupters use photo-transistors or
photo-darlingtons with open collector outputs. The fancier ones have
amplifiers and logic level outputs.
The HP sensors are pretty sophisticated, there are a number of detectors
at the proper spacing for the chopper wheel pitch, so that you still get
a clean output if there is junk on the chopper wheel or the sensor.
Bob
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Posted by Curt Welch on August 17, 2008, 12:56 pm
> Hi,
> I'm a software guy groping around in EE-land,
Me too.
> and I could use a little
> help.
> A few old inkjet printers yielded up some nice motors with optical
> rotary encoders built in. There are only six wires coming from the
> connector on the back of the motor/encoder. Two of the wires go
> directly to the DC motor. The other four are for the I-R emitter and
> the two I-R detectors. Here are some lovely photos, in case they help:
> http://www.minsmithphoto.com/mrintj/encoder-top.jpg
> http://www.minsmithphoto.com/mrintj/encoder-back.jpg
> http://www.minsmithphoto.com/mrintj/encoder-bottom.jpg
> Using a low-voltage diode tester, and squinting at the traces on the
> circuit board, I came up with the following circuit diagram...
> http://www.minsmithphoto.com/mrintj/schematic.png
> I've powered up the emitter, put an ohmmeter on one of the photodiodes
> (in forward polarity), and watched the resistance go from high to low
> as I slowly turn the motor shaft.
> Even though it seems to work, I can't help but feel that something is
> wrong. I would have expected the two photodiodes to share a common
> anode or cathode, but that doesn't seem to be the case. Also, I'm
> puzzled as to why they would be connected in the direction that they
> are - so that I'd need a supply greater than +5V to read D1 and a
> negative supply to read D3?
I don't know much of anything about these, but reading the wikipedia
article on photo diodes, it points out that a common mode of operation is
to reverse bias the diodes. As they are connected, they would be reverse
biased so it doesn't look backwards to me. You seem to be assuming they
must be forward biased to work.
I can only guess they are wried that way to drive some type of differential
sensor circuit.
> What am I doing wrong? I'm assuming that the detectors (on the bottom
> of the opto-interrupter assembly, closest to the circuit board) *are*
> two individual photo diodes. An EE at work suggested that they may be
> ICs with built-in amplifiers, etc...
Do they act like photo diodes when you test them without applying the power
to the +5 and GND? Maybe by shining a bright light or sunlight (to get IR
wavelengths) on them? If so, your schematic is probably correct. If it
needs the power to operate, it might be some type of receiver circuit
instead of the dual diodes you are assuming.
--
Curt Welch http://CurtWelch.Com/
curt@kcwc.com http://NewsReader.Com/
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>
> I'm a software guy groping around in EE-land, and I could use a little
> help.
>
> A few old inkjet printers yielded up some nice motors with optical
> rotary encoders built in. There are only six wires coming from the
> connector on the back of the motor/encoder. Two of the wires go
> directly to the DC motor. The other four are for the I-R emitter and
> the two I-R detectors. Here are some lovely photos, in case they help:
>
> http://www.minsmithphoto.com/mrintj/encoder-top.jpg
> http://www.minsmithphoto.com/mrintj/encoder-back.jpg
> http://www.minsmithphoto.com/mrintj/encoder-bottom.jpg
>
> Using a low-voltage diode tester, and squinting at the traces on the
> circuit board, I came up with the following circuit diagram...
>
> http://www.minsmithphoto.com/mrintj/schematic.png
>
> I've powered up the emitter, put an ohmmeter on one of the photodiodes
> (in forward polarity), and watched the resistance go from high to low
> as I slowly turn the motor shaft.
>
> Even though it seems to work, I can't help but feel that something is
> wrong. I would have expected the two photodiodes to share a common
> anode or cathode, but that doesn't seem to be the case. Also, I'm
> puzzled as to why they would be connected in the direction that they
> are - so that I'd need a supply greater than +5V to read D1 and a
> negative supply to read D3?
>
> Surely, I've made a mistake somewhere, but when I go back through the
> process of measuring and visual inspection, I end up with the same
> goofy schematic.
>
> What am I doing wrong? I'm assuming that the detectors (on the bottom
> of the opto-interrupter assembly, closest to the circuit board) *are*
> two individual photo diodes. An EE at work suggested that they may be
> ICs with built-in amplifiers, etc...
>