The Sensor Olympics 2 — Going the Distance
ubiquitous GP2D12 sensors, with comparatively
improved range and reduced output
fluctuations. The 2YOA21 sensors can sense
obstacles in the range between 5 cm and 150
cm. The output voltage from the sensor can be
converted into a range in centimeters using a
simple calculation. The comprehensive
datasheet for the sensor comes with all of this
information and more, just as much a font of
useful physics info and unsolicited trivia as Dr.
To compare this sophisticated sensor to
the Scribbler’s more rudimentary array seemed
like comparing apples to oranges. It seemed
like a foregone conclusion that the 2YOA21
would have a better range, which was the
intuitive metric for comparison. However, that
very conflict inspired us as to what a useful
comparison would be. The 2YOA21 was the
type of top shelf sensor one might order
specifically for a project, knowing that it will be
up to snuff and super effective but the
mysterious phototransistors in the Scribbler
were more akin to the type of sensors that
you might find buried in your toolbox –
incidental discoveries when you are looking
for something just good enough to get the
It seemed like a useful question to have
answered – can random toolbox sensors
compete with cutting-edge improvements on
popular designs? We wouldn’t necessarily look
at range and other metrics often covered in
datasheets, but rather we wanted to see how
these sensors dealt with non-ideal conditions.
Sure the Scribbler and Mark III can avoid bright
walls well enough, but what about more ephemeral
PROGRAMMING THE SCRIBBLER WITH AN OBSTACLE AVOIDANCE PROGRAM.
PROGRAMMING THE MARK III WITH AN OBSTACLE AVOIDANCE PROGRAM.
No Block on the Horizon
Before we moved on to more whimsical obstacles, we
wanted to get a baseline for performance using a standard
obstacle – something bright, something solid, something to
bring relief on those sniffly days. A tissue box suited our
purposes perfectly. To accurately track when our bots saw
the obstacle, we marked distances in centimeters on the
back of our line following track, and then we were ready
to let the arch rivals duke it out once again. We started
with the Scribbler. The LEDs and sudden backtracking
made it obvious when the bot saw the box, and we marked
off the distance over a number of trials. The Scribbler
sensed the obstacle at distances ranging from 35 cm to 45
cm away, but showed a lot of variation within that range.
The Scribbler did, however, always sense the obstacle and
did not make the embarrassing gaffe of running headlong
into the box.
THE MARK III'S RANGEFINDERS ARE LOOKING SHARP.
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