[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.

We don’t know if [Hanna Yatco] has a good sense of balance or not, but we do know her Arduino does. Her build uses the ubiquitous HC-SR04 SONAR sensor and a servo. This is a great use for a ...