Servo - September 2012

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.