The JSN has a blind zone of roughly 20-25 cm. Anything closer and it either returns nonsense or nothing. HC-SR04 goes down to 2 cm, that’s why the bench test lies to you.
Modbus is just registers until it isn't.
The JSN has a blind zone of roughly 20-25 cm. Anything closer and it either returns nonsense or nothing. HC-SR04 goes down to 2 cm, that’s why the bench test lies to you.