Here is a simple Android Bluetooth Remote Control Project for 4 Relays / Device using 89c2051 Micro-controller and HC-05 Bluetooth Module.

You can download circuit and hex file here http://www.hobbyprojects.com/bluetooth-device-control/

App Instructions:

1. First make sure your HC-05 Bluetooth Module is paired with your mobile. The default password for pairing is "1234" or "0000". Check the manual of Bluetooth module.

2. When you press ON button for Device 1 it sends the data "A" to Bluetooth Module connected with a circuit. Microcontroller turns ON the Device 1 relay when it detects "A".

3. When you press OFF button for Device 1 it sends the data "a" to Bluetooth Module connected with a circuit. Microcontroller turns OFF the Device 1 relay when it detects "a".

4. When you press ON button for Device 2 it sends the data "B" to Bluetooth Module connected with a circuit. Microcontroller turns ON the Device 2 relay when it detects "B".

5. When you press OFF button for Device 2 it sends the data "b" to Bluetooth Module connected with a circuit. Microcontroller turns OFF the Device 2 relay when it detects "b".

6. When you press ON button for Device 3 it sends the data "C" to Bluetooth Module connected with a circuit. Microcontroller turns ON the Device 3 relay when it detects "C".

7. When you press OFF button for Device 3 it sends the data "c" to Bluetooth Module connected with a circuit. Microcontroller turns OFF the Device 3 relay when it detects "c".

8. When you press ON button for Device 4 it sends the data "D" to Bluetooth Module connected with a circuit. Microcontroller turns ON the Device 4 relay when it detects "D".

9. When you press OFF button for Device 4 it sends the data "d" to Bluetooth Module connected with a circuit. Microcontroller turns OFF the Device 4 relay when it detects "d".