18. IoT Case 09: Smart House door control

Level: level auto_fit

18.1. Goal

Use app inventor to create an APP to control the door of the house.

18.2. Background

What is app inventor?

App Inventor allows user to develop their own app for Android phones or IOS device(iphone, ipad) by simple programming and design work.

Smart House door operation

When the micro:bit receives the signal “opendoor” from the app, the 180o servo will turn for 180o to open the door. When the micro:bit receives the signal “closedoor” from the app, the 180o servo will turn back 180o to close the door.


18.3. Part List


18.4. Assembly step

Step 1

Attach the L-shaped stand with M3 screws and nuts to the model H1. Make a small hole to fix into the stand securely.


Step 2

Attach the servo to the model H1.


Step 3

Straighten the paper clip and cut it to 6.5 cm. Use pilers to fix the paper clip into the L-shaped stand.


Step 4

Put together all the cardboard parts (H1-H2)


Step 5

Assembly completed!


18.5. Hardware connect

Connect the 180ᵒ servo to P2 port of IoT:bit

Micro:bit P2 Servo
S (yellow) S (orange)
V (red) V (red)
G (black) G (brown)


18.6. Programming (MakeCode)

Step 1. Initialize OLED, IoT:bit and connect to WiFi

  • Snap Initialize OLED with width:128, height: 64 to on start

  • Snap Initialize IoT:bit TX P16 RX P8 from IoT:bit to on start

  • Snap Set Wi-Fi to ssid pwd from IoT:bit

  • Enter your Wi-Fi name and password. Here we set smarthon as SSID and 12345678 as password pic_60

Step 2. Set servo initial position

  • Snap Turn Servo to degree from SmartCity > Output

  • Turn servo to 180 degree at pin P2 (the servo will control the door to be closed initially) pic_60

Step 3. Show icon “tick” after WiFi connection

  • Snap show icon from basic to On WiFi connected and select icon tick

  • Draw the Device ID variable from On WiFi connected to the show string block placeholder pic_60

Step 4. Receive WAN command

  • Go to OLED

  • Snap the clear OLED display to On WiFi received to avoid overlap

  • Snap the show string to On WiFi received

  • Draw the WAN_Command variable to show string placeholder pic_80

Step 5. Open/close door by WAN command

  • If Wan command opendoor is received, turn servo to 45 degree at P2 (open door angle)

  • If Wan command closedoor is received, turn servo to 180 degree at P2 (close door angle) pic_80

Full Solution



18.7. IoT (App Inventor)

* For more details, please refer to “Chapter 3: Direct control micro:bit by App Inventor 2”

Step 1

Create the page with the components

  • On Designer:

  • Drag the components from the left menu – we will need buttons to open or close the door and a textbox for input the Device ID number.

  • Also, add the invisible component “Web” under connectivity, we will need it for WAN connection. auto_fit

Step 2

Make the programming part

  • On Blocks:

  • The WAN control command URL is: http://control.smarthon.cc/publish?id=DeviceID&msg=ControlCommand

  • When Button1 is clicked, it will direct to the URL with given device ID and command “opendoor”. auto_fit

  • When Button2 is clicked, it will direct to the URL with given device ID and command “closedoor”. auto_fit

  • Download the App in your phone to by .apk or scan QR code. auto_fit

18.8. Result

Input your device ID number in the textbox, then click button “opendoor” to send command “opendoor”. Click button “Close Door” to send command “closedoor”.



With app inventor and micro:bit, you can control the door open/close by mobile app!


18.9. Think

Q1. How can we add password authentication to open the door?

Q2. We can install the servo to different position in the house (tips: modify the turning angle of the servo)