Cheap stuff gets our creative juices flowing. Case in point? [Andy Grove] built an eight-sensor HC-SR04 breakout board, because the ultrasonic distance sensors in question are so affordable that a … ...

Using a Raspberry Pi mini PC together with inexpensive HC-SR04 ultrasonic sensors as inputs, the system generates MIDI notes which can be played through a synthesizer on the Pi to output high ...

It uses a Raspberry Pi and an HC-SR04 ultrasonic sensor to monitor the water level in a sump pit, log the readings and send SMS e-mail alerts if the water rises above a predefined level.