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.
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