HC-05 Bluetooth Module – Normal

Introduction

• It is used for many applications like wireless headsets, game controllers, wireless mouse, wireless keyboards, and many more consumer applications.
• It is IEEE 802.15.1 standardized protocol, through which one can build wireless Personal Area Network (PAN). It uses frequency-hopping spread spectrum (FHSS) radio technology to send data over air.
• It uses serial communication to communicate with devices. It communicates with a microcontroller using serial port (USART).

Specification

• Voltage: 3.6 V-6 V connected to the VCC pin
• Communication leads are working with voltage 3.3 V (tolerate 5 V)
• Current consumption: approx. 50 mA
• Class 2 – maximum transmitter power + 4 dBm
• Range: up to 10 m
• The password for pairing: 1234
• Standard: Bluetooth 2.0 + EDR
• The SPP profile with the possibility to configure via AT commands
• Communication: UART (RX, TX)
• Small dimensions: 39 x 16 mm

HC-05 Bluetooth Module Pin Diagram
Bluetooth serial modules allow all serial-enabled devices to communicate with each other using Bluetooth.

It has 6 pins:

1. Key/EN: It is used to bring Bluetooth module in AT commands mode. If Key/EN pin is set to high, then this module will work in command mode. Otherwise by default it is in data mode. The default baud rate of HC-05 in command mode is 38400bps and 9600 in data mode. HC-05 module has two modes:
   1. Data mode: Exchange of data between devices.
   2. Command mode: It uses AT commands which are used to change setting of HC-05. To send these commands to module serial (USART) port is used.
2. VCC: Connect 5 V or 3.3 V to this Pin.
3. GND: Ground Pin of module.
4. TXD: Transmit Serial data (wirelessly received data by Bluetooth module transmitted out serially on TXD pin)
5. RXD: Receive data serially (received data will be transmitted wirelessly by Bluetooth module).
6. State: It tells whether module is connected or not.

HC-05 module Information

• HC-05 has red LED which indicates connection status, whether the Bluetooth is connected or not. Before connecting to HC-05 module this red LED blinks continuously in a periodic manner. When it gets connected to any other Bluetooth device, its blinking slows down to two seconds.
• This module works on 3.3 V. We can connect 5V supply voltage as well since the module has on board 5 to 3.3 V regulator.
• As HC-05 Bluetooth module has 3.3 V level for RX/TX and microcontroller can detect 3.3 V level, so, no need to shift transmit level of HC-05 module. But we need to shift the transmit voltage level from microcontroller to RX of HC-05 module.

Pair HC-05 and Smartphone:

1. Search for new Bluetooth device from your phone. You will find Bluetooth device with “HC-05” name.
2. Click on connect/pair device option; default pin for HC-05 is 1234 or 0000
3. After pairing two Bluetooth devices, open terminal software (e.g. Teraterm, Realterm etc.) in PC, and select the port where we have connected USB to serial module. Also select default baud rate of 9600 bps.
4. In smart phone, open Bluetooth terminal application and connect to paired device HC-05.
5. It is simple to communicate, we just have to type in the Bluetooth terminal application of smartphone. Characters will get sent wirelessly to Bluetooth module HC-05. HC-05 will automatically transmit it serially to the PC, which will appear on terminal. Same way we can send data from PC to smartphone.

Command Mode

• When we want to change settings of HC-05 Bluetooth module like change password for connection, baud rate, Bluetooth device’s name etc.
• To do this, HC-05 has AT commands.
• To use HC-05 Bluetooth module in AT command mode, connect “Key” pin to High (VCC).
• Default Baud rate of HC-05 in command mode is 38400bps.
• Following are some AT command generally used to change setting of Bluetooth module.
• To send these commands, we have to connect HC-05 Bluetooth module to the PC via serial to USB converter and transmit these command through serial terminal of PC.