As an obstacle detector, this sensor has range issues
with black or dark objects, so it would be wise to have a
companion sensor; either ultrasonic or Sharp IR sensors,
which are less color sensitive. Personally, I see more
potential in using it as a long-range Scotchlite reflector
sensor.
My outdoor tests to sense a Scotchlite retroreflective
sticker in sunny conditions showed a working range of over
60 feet in my wiggly handheld tests. Probably more if the
sensor and reflector are firmly fastened down. You could
easily make a long distance break-beam sensor system,
either a perimeter alarm, or (as my drone-racing buddy Jon
suggested) a finish line timing sensor. There are many
possible applications.
In the toy business, when a
product has a quirk, we often say “if
you can’t fix it, feature it.” This
sensor’s color sensitivity may work
against it as an obstacle detector,
but in the right situation it brings
something new to the party. My
first order of business was to try it
on a line following robot.
Using just one sensor seeing
black or white, it would have to be
an edge detector. I built the small
tricycle robot shown in the opening
shot and Figure 6. The front drive
wheel is steered via servo and the
sensor is mounted overhead to steer
along with the wheel. It is used
without the lens and looks
downward at the line about an inch
ahead of the wheel. The tiny
PICAXE program in Figure 7 follows
the right edge of a
wide black line quite
simply by zigging left
when white is seen and
zagging right when
black is seen.
My video
demonstration at
https://www.youtube.com/watch?v=
Q5tBp2_Ya0Y shows the line follower steering
system is in constant oscillation; somewhat like
the old “galloping ghost” control system used in
the earliest days of radio control:
https://www.youtube.com/watch?v=
IBxXsRwRn1M.
That wiggling is the price you pay for such a
minimalist one-sensor edge following system. If
we could add more sensors, it would help reduce
oscillation. Unfortunately, these laser sensors
interfere if they overlap each other’s field of view,
so we’re stuck with using one sensor — unless you
want to multiplex several sensors so only one laser
is on at a time. I did that on an S6986 based laser tracker
project you can see at https://www.youtube.com/
watch?v=5IvkHokhZsQ.
Back to the single laser sensor, vehicle dynamics could
be improved by adding a second servo and decoupling the
sensor from the wheel. In this system, the extra servo
would oscillate/scan the sensor across the line edge while
the steering servo holds a more stable position.
There are much faster line following robots out there;
my “waddling duck” (as someone named it in the PICAXE
I’ve taught students in college
and I know it’s easier to engage
whole classes when projects are
simple and seemingly obvious.
When people say “even I could build
that,” I’ve done my job.
In similar fashion, I wanted to
make a simple optical scanner using
this laser sensor. Its sensitivity to
color makes it a low resolution
digitizer of sorts. There’s no
electronic sensitivity or contrast
adjustment for what’s detected as
black versus white; it triggers at a
preset value of reflected laser signal.
That signal will vary based on
the color and reflectivity of the
object seen, as well as the distance
to the object. I settled for scanning
a simple B/W image of our
12 SERVO 04.2017
Figure 9.
Figure 8.
Figure 7.
Figure 6.