This project is very easy but useful.
Prepare 1 D-duino
Step 1: Follow Github Project
Then follow this project ESP8266 QRcode
Step 2: Check With Your Smartphone
Do not forget change SDA,SCL pin to D1, D2. D-duino can show a lot of information from WiFi.
You can add useful information to your code.
Then check with your smartphone.
See, I can read Helloworld.