HCSR04 Ultrasonic Transducer

Shows how to use an HCSR04 module to measure distances.

Warning

Ultrasonic_HCSR04 modules usually work with 5v power and TTL levels, so You need voltage divider or level shifter for ECHO pin.

Trigger pin is tolerant for 3.3v and in my case work without problems

By nik.sharky http://esp8266.ru/forum/members/sharky.396/

References