Introduction The SRF05-HY is an evolutionary step from the SRF04-HY, and has been designed to increase flexibility, increase range, and to reduce costs still further. As such, the SRF05-HY is fully compatible with the SRF04-HY (HC-SR04). Range is increased from 3 meters to 4 meters. A new operating mode (tying the mode pin to ground) allows the SRF05-HY to use a single pin for both trigger and echo, thereby saving valuable pins on your controller. When the mode pin is left unconnected, the SRF05-HY operates with separate trigger and echo pins, like the SRF04. The SRF05-HY includes a small delay before the echo pulse to give slower controllers such as the Basic Stamp and Picaxe time to execute their pulse in commands.