A 28-minute build
Control lights and a fan from your phone
You'll build a mini smart home: three lights and a fan, switched on and off from an Android phone over Bluetooth. You add one part at a time and test it before moving on.
📱 You need an Android phone. The HC-05 Bluetooth module uses
“classic” Bluetooth, which does not work with iPhones.
Safety first
- This is low voltage only: one 3.7 V battery and the USB cable. Never connect anything to a wall socket. The “Live (red)” and “Neutral (black)” labels in the kit are just wire colours.
- Unplug the USB cable before you add or move any wires.
- Don't short the battery: never let its + and − wires touch. If the battery gets hot, take it out of the holder and tell your teacher.
How it works
Phone app→HC-05 Bluetooth→Arduino UNO→Relays→Lights & fan
The phone sends a letter, like B. The Arduino reads it and flips a relay. The relay switches the battery's power to a light or the fan.
Parts
- Arduino UNO + USB cable (must be a data cable, not charge-only)
- HC-05 Bluetooth module
- 4-channel relay module (blue)
- Short breadboard and jumper wires
- 3 LEDs and 4 × 220 Ω resistors (you use 3; one is spare)
- Mini fan motor
- Red and black wires
- 18650 battery (3.7 V) in its holder
- A Windows PC with Arduino IDE 2.x, and an Android phone
The steps
- 0Check the board uploads5 min
- 1Relay module only4 min
- 2First light4 min
- 3Lights 2 and 34 min
- 4Fan3 min
- 5Bluetooth5 min
- 6Final code3 min