Make sure jumper cap connected E_TX to D4 and E_RX to D5.
Connect the HC-SR04 with UNO as following diagram:
| UNO Board |
HC-SR04 |
| 5v |
VCC |
| GND |
GND |
| D8 |
Trig |
| D7 |
Echo |
Software Installation
Step A）Install latest Arduino IDE (If you have Arduino IDE version after 1.1.16, please skip this step).Download Arduino IDE from https://www.arduino.cc/en/Main/Software?setlang=en, then install the software.
Step B) Connect the Arduino UNO board to computer via USB cable,
Step C) Open the Arduino IDE and choose corresponding board type and port type for you project.
- Board:”Arduino/Genuino UNO”
- Port: Choose your own Serial Port for your UNO board
Step D) Download the sketch file fromhttps://osoyoo.com/driver/Esp8266_Arduino_IOT/lesson9/esp8266-lesson9.zip
unzip the file and double click the esp8266-lesson9.ino file, load the sketch into Arduino IDE, find following lines:
char ssid[] = "******"; // your network SSID (name)
char pass[] = "******"; // your network password
please replace the ****** with your correct wifi SSID and password, otherwise your project can
not connect to Internet.
Step E) After change above lines, load the sketch into Arduino IDE.
Open your Serial Monitor, you can see your router will assign an IP address to your Arduino as following: 
In above example, 192.168.50.116 is the IP address of my Arduino.
Now put an obstacle in front of the sensor and use another computer or your cell phone’s browser to visit url : http://192.168.50.116 Your browser will show following result which tells you the distance between sensor and obstacle:
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