5 mm square, more or less.
These need biasing in a similar
manner as the QRB-1134
devices. The datasheet for the
EE-SY124 is a great deal more
difficult to understand but
many of the stated values and
test criteria were very similar,
so I tried our 470 ohm LED
resistor and 47K sensor resistor.
Figure 8. Wheel encoder
I keep a supply of SMT (surface-mount) parts on hand
which looked perfect for this quick lash-up project. This
configuration works quite well. Unlike the QRB-1134, the
EE-SY124 documentation suggests putting the bias resistor
on the emitter side of the sensor so that you get a logic
high when you have high reflection (light). My tests showed
that my “dark” logic low was 0.43V and my “light” logic
high was 4.77V. This sensor, however, was much more
sensitive to the distance from the surface that it is sensing.
It appeared to work well at about 1 mm distance and the
logic high voltage fell off very sharply as you got closer to
or further away from its “sweet” spot. Figure 8 shows what
my quick build encoder sensor looks like. I plan on attaching
these to my hacked hobby servos using R/C servo tape.
That stuff is very thin and VERY strong when used like this.
In case you were wondering, the schematics for the circuits
that I used in researching this question are shown in Figure 9.
Figure 9. Schematics for the two sensors.
I may have answered the question with more
information that what was expected. However, sometimes
you get caught up in the thrill of discovery, or perhaps
the overwhelming urge to be clever just can’t be stopped.
There was information that I discovered during my
experiments that I felt would be useful to everyone.
Finding that postscript encoder wheel program was worth
the time all by itself! Have fun and may you always know
where your robot is.
If you have any questions of your own, please go
ahead and send us an email to roboto@servomagazine.
SERVO 06.2008 17