Cargo Features

[dependencies]
hcsr04_async = { version = "0.3.1", default-features = false, features = ["blocking_trigger"] }
default = blocking_trigger

The blocking_trigger feature is set by default whenever hcsr04_async is added without default-features = false somewhere in the dependency tree.

blocking_trigger default

blocking trigger pulse, recommended for most use cases. Much more accurate trigger pulse length.