Features
- Wireless communication module for easy and reliable Bluetooth connectivity
- Compact and lightweight design for easy integration in embedded systems, robotics, and other applications
- Six pins for easy integration with other components
- Frequency of 2.4GHz ISM band, allowing for high-speed wireless communication
- Modulation of GFSK (Gaussian Frequency Shift Keying) for reliable and efficient data transfer
- Emission power of ≤4dBm, Class 2, for a range of up to 10 meters, depending on the environment
- Sensitivity of ≤-84dBm at 0.1% BER, ensuring reliable communication in noisy environments
- Speed of up to 2.1Mbps (Max) for asynchronous communication, and up to 1Mbps for synchronous communication
- Authentication and encryption for secure communication
- Profiles for Bluetooth serial port, allowing for easy integration with other devices
- Operates on a supply voltage range of +3.3V to 6.0V, compatible with a wide range of microcontrollers and other electronic devices
- Low supply current of 30mA for efficient power consumption
- Working temperature range of -20 ~ +75 Centigrade for use in a variety of environments
- Follows IEEE 802.15.1 standardized protocol, allowing for building wireless Personal Area Networks (PANs)
- Uses frequency-hopping spread spectrum (FHSS) radio technology for reliable and efficient data transfer over the air
Principle of Work
The Bluetooth HC-05 Module operates on the principle of wireless communication using Bluetooth technology. When connected to a device, the module uses frequency-hopping spread spectrum (FHSS) radio technology to send and receive data over the air. The module communicates with other Bluetooth-enabled devices using a standardized protocol, IEEE 802.15.1 and employs a Gaussian Frequency Shift Keying (GFSK) modulation scheme to efficiently transfer data. The module supports both asynchronous and synchronous communication, with a maximum speed of up to 2.1Mbps for asynchronous communication, and up to 1Mbps for synchronous communication. To ensure secure communication, the HC-05 module provides authentication and encryption mechanisms. This makes it a reliable and secure option for wireless communication needs.
Pinout of the Module

- VCC: Power supply pin (typically 5V, has onboard regulator)
- GND: Ground pin
- TXD: Transmit pin (data out)
- RXD: Receive pin (data in, not 5V tolerant)
- KEY: Enables AT command mode when pulled high
- STATE: Indicates connection state (high in AT mode, low in data mode)
Note: Use a voltage divider or level shifter to connect RXD to 5V logic.
Applications
- Wireless data transfer
- Wireless control (e.g., robots, home automation)
- IoT applications
- Wireless audio streaming
- Wearable devices
- Automotive applications
Circuit
- LED anode → Digital Pin 8
- LED cathode → 220Ω resistor → GND
- HC-05 VCC → Arduino 5V
- HC-05 GND → Arduino GND
- HC-05 TXD → Arduino Pin 2
- HC-05 RXD → Voltage divider → Arduino Pin 3
- HC-05 KEY → 3.3V

Library
Uses the built-in SoftwareSerial
library. No external installation required.
Example Code
#include <SoftwareSerial.h>
#define LED_PIN 8
#define HC05_RX_PIN 2
#define HC05_TX_PIN 3
SoftwareSerial mySerial(HC05_TX_PIN, HC05_RX_PIN);
void setup() {
pinMode(LED_PIN, OUTPUT);
Serial.begin(9600);
mySerial.begin(9600);
}
void loop() {
if (Serial.available() > 0) {
char data = Serial.read();
if (data == '1') {
digitalWrite(LED_PIN, HIGH);
} else if (data == '0') {
digitalWrite(LED_PIN, LOW);
}
}
}
How to Connect with Android
- Install “Serial Bluetooth Terminal” or “Bluetooth Terminal HC-05”
- Turn on phone’s Bluetooth
- Search and pair with “HC-05” using code “1234” or “0000”
- Open terminal and send '1' to turn ON LED, '0' to turn OFF
Technical Details
- Frequency: 2.4GHz ISM band
- Modulation: GFSK
- Emission Power: ≤4dBm (Class 2)
- Sensitivity: ≤-84dBm at 0.1% BER
- Speed: 2.1Mbps (async) / 1Mbps (sync)
- Security: Authentication and encryption
- Profiles: Bluetooth serial port
- Voltage: +3.3V to 6.0V
- Current: 30mA
- Temperature: -20°C to +75°C
- Dimensions: 26.9mm x 13mm x 2.2mm
Comparison with HC-06
- Role: HC-05 (Master/Slave), HC-06 (Slave only)
- Pin Count: HC-05 (6), HC-06 (4)
- Default Mode: HC-05 (Transparent), HC-06 (Command)
- Price: HC-05 is more expensive
- Range: HC-05 (up to 100m), HC-06 (around 10m)
Features
- Wireless communication module for easy and reliable Bluetooth connectivity
- Compact and lightweight design for easy integration in embedded systems, robotics, and other applications
- Six pins for easy integration with other components
- Frequency of 2.4GHz ISM band, allowing for high-speed wireless communication
- Modulation of GFSK (Gaussian Frequency Shift Keying) for reliable and efficient data transfer
- Emission power of ≤4dBm, Class 2, for a range of up to 10 meters, depending on the environment
- Sensitivity of ≤-84dBm at 0.1% BER, ensuring reliable communication in noisy environments
- Speed of up to 2.1Mbps (Max) for asynchronous communication, and up to 1Mbps for synchronous communication
- Authentication and encryption for secure communication
- Profiles for Bluetooth serial port, allowing for easy integration with other devices
- Operates on a supply voltage range of +3.3V to 6.0V, compatible with a wide range of microcontrollers and other electronic devices
- Low supply current of 30mA for efficient power consumption
- Working temperature range of -20 ~ +75 Centigrade for use in a variety of environments
- Follows IEEE 802.15.1 standardized protocol, allowing for building wireless Personal Area Networks (PANs)
- Uses frequency-hopping spread spectrum (FHSS) radio technology for reliable and efficient data transfer over the air
Principle of Work
The Bluetooth HC-05 Module operates on the principle of wireless communication using Bluetooth technology. When connected to a device, the module uses frequency-hopping spread spectrum (FHSS) radio technology to send and receive data over the air. The module communicates with other Bluetooth-enabled devices using a standardized protocol, IEEE 802.15.1 and employs a Gaussian Frequency Shift Keying (GFSK) modulation scheme to efficiently transfer data. The module supports both asynchronous and synchronous communication, with a maximum speed of up to 2.1Mbps for asynchronous communication, and up to 1Mbps for synchronous communication. To ensure secure communication, the HC-05 module provides authentication and encryption mechanisms. This makes it a reliable and secure option for wireless communication needs.
Pinout of the Module

- VCC: Power supply pin (typically 5V, has onboard regulator)
- GND: Ground pin
- TXD: Transmit pin (data out)
- RXD: Receive pin (data in, not 5V tolerant)
- KEY: Enables AT command mode when pulled high
- STATE: Indicates connection state (high in AT mode, low in data mode)
Note: Use a voltage divider or level shifter to connect RXD to 5V logic.
Applications
- Wireless data transfer
- Wireless control (e.g., robots, home automation)
- IoT applications
- Wireless audio streaming
- Wearable devices
- Automotive applications
Circuit
- LED anode → Digital Pin 8
- LED cathode → 220Ω resistor → GND
- HC-05 VCC → Arduino 5V
- HC-05 GND → Arduino GND
- HC-05 TXD → Arduino Pin 2
- HC-05 RXD → Voltage divider → Arduino Pin 3
- HC-05 KEY → 3.3V

Library
Uses the built-in SoftwareSerial
library. No external installation required.
Example Code
#include <SoftwareSerial.h>
#define LED_PIN 8
#define HC05_RX_PIN 2
#define HC05_TX_PIN 3
SoftwareSerial mySerial(HC05_TX_PIN, HC05_RX_PIN);
void setup() {
pinMode(LED_PIN, OUTPUT);
Serial.begin(9600);
mySerial.begin(9600);
}
void loop() {
if (Serial.available() > 0) {
char data = Serial.read();
if (data == '1') {
digitalWrite(LED_PIN, HIGH);
} else if (data == '0') {
digitalWrite(LED_PIN, LOW);
}
}
}
How to Connect with Android
- Install “Serial Bluetooth Terminal” or “Bluetooth Terminal HC-05”
- Turn on phone’s Bluetooth
- Search and pair with “HC-05” using code “1234” or “0000”
- Open terminal and send '1' to turn ON LED, '0' to turn OFF
Technical Details
- Frequency: 2.4GHz ISM band
- Modulation: GFSK
- Emission Power: ≤4dBm (Class 2)
- Sensitivity: ≤-84dBm at 0.1% BER
- Speed: 2.1Mbps (async) / 1Mbps (sync)
- Security: Authentication and encryption
- Profiles: Bluetooth serial port
- Voltage: +3.3V to 6.0V
- Current: 30mA
- Temperature: -20°C to +75°C
- Dimensions: 26.9mm x 13mm x 2.2mm
Comparison with HC-06
- Role: HC-05 (Master/Slave), HC-06 (Slave only)
- Pin Count: HC-05 (6), HC-06 (4)
- Default Mode: HC-05 (Transparent), HC-06 (Command)
- Price: HC-05 is more expensive
- Range: HC-05 (up to 100m), HC-06 (around 10m)