“HC-SR04 ultrasonic sensor modules, also commonly called ping sensors, are practically a dime a dozen, with many Asia online retailers selling them in the $2 to $3 dollar range each. While possibly not intended for an end solution or product, these sensors offer a more affordable option for prototyping and application development compared to the original and possibly more well-known ping sensor sold by Parallax, or transducers sold by Maxbotix. “