M
Mr. INTJ
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 six are for the I-R emitter and
the two I-R detectors. Here are some lovely photos, in case it helps:
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 done something wrong, but when I go back through the
process of measuring and visual inspection, I get 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
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 six are for the I-R emitter and
the two I-R detectors. Here are some lovely photos, in case it helps:
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 done something wrong, but when I go back through the
process of measuring and visual inspection, I get 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