WIRING UP THE SRF-05.
The Cobra Strikes Again
READY FOR THE DOHYO.
together a driving base to carry it around. Having a
driving base ready and waiting for such a task allows us to
focus on the sensors or mechanism, making the entire
process less tedious and more productive.
If the Cobra was to be suitable as a platform for
experimentation, we could envision some unique
advantages based on its design. The Cobra — by its nature
— is a competitive bot. The powerful motors and durable
base distinguish it from the LEGO or VEX bases that we
would often put together when we needed a driveable
platform. Especially when a new sensor or mechanism
might make its eventual home on a competitive bot, an
experimental platform more closely approximating the
final product could be beneficial.
With this in mind, we wanted to see if the Cobra
chassis could provide such a platform, and we had just the
sensor for the job — the SRF-05 ultrasonic sensor from
Devantech. We’ve always thought that ultrasonic sensors
have something of an exotic allure to them. IR sensors are
a classic solution to giving your bot the ability to avoid (or
track) obstacles, and even though the theory behind an
ultrasonic sensor is similar on the most general level,
giving your bot a sense of hearing
carries its own sense of excitement.
The SRF-05 is an upgrade from
the popular SRF-04 ultrasonic
sensor, and it works by sending out
an ultrasonic ping, receiving the
reflected ping, and using the time
difference to calculate the distance
to an obstacle. The SRF-05 improves
upon the SRF-04 in a number of
ways. It has an increased range of
up to 13 feet; it has modest power
requirements with a 5V input and
only 4 mA operating current; and it
can be wired up in a four- or five-wire configuration. In interests of
wiring economy, we elected to go with the four-wire
configuration which requires a wire for power, one for
ground, a second for a chassis ground, and a final wire
that we refer to for convenience as the signal wire.
PROGRAMMING THE COBRA.
SERVO 09.2012 71