[Emil] got his hands on a dozen HC-SR04 ultrasonic sensors, but wasn’t too happy with their performance. Rather than give up, he reverse engineered the sensor and built an improved version. H… ...

You can choose between the one or two pin approach with the HY-SRF05 Ultrasonic sensors which cost roughly the same as the HC-SR04, so it seems a little odd to hack the SR04 instead of picking up ...