HCSR04 Ultrasonic Transducer¶
Shows how to use an HCSR04 module to measure distances.
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/