The HC-05 is a Bluetooth module manufactured by BLUETOOTH, with the part ID HC-05. It is a versatile and widely used component for enabling wireless communication between devices. Operating in the 2.4 GHz frequency range, the HC-05 supports both master and slave modes, making it suitable for a variety of applications. It is commonly used in embedded systems to connect microcontrollers, such as Arduino boards, to smartphones, laptops, or other Bluetooth-enabled devices.
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This circuit features a Raspberry Pi Pico microcontroller interfaced with an HC-05 Bluetooth module for wireless communication, an HMC5883L compass module for magnetic field measurement, and a GPS NEO 6M module for location tracking. The Pico is configured to communicate with the HC-05 via serial connection (TX/RX), with the compass module via I2C (SCL/SDA), and with the GPS module via serial (TX/RX). Common power (VCC) and ground (GND) lines are shared among all modules, indicating a unified power system.
This circuit connects an HC-05 Bluetooth module to an Arduino UNO for wireless communication. The HC-05's VCC and GND are connected to the Arduino's 5V and GND, respectively, for power. The TXD pin of the HC-05 is connected to the Arduino's D1 (RX) pin, and the RXD pin of the HC-05 is connected through a voltage divider made of two resistors to the Arduino's D0 (TX) pin, allowing for serial communication between the two devices.
This circuit features an Arduino UNO microcontroller interfaced with an HC-05 Bluetooth module for wireless communication. It also includes two 5V two-channel relay modules, which are connected to the Arduino for controlling external devices. The setup allows for remote control of devices via Bluetooth.
This circuit connects an HC-05 Bluetooth Module to an Arduino UNO for wireless communication. The HC-05's VCC and GND are connected to the Arduino's 5V and GND for power. The HC-05's TXD and RXD pins are connected to the Arduino's D11 and D10 pins, respectively, allowing for serial communication between the two devices.
The HC-05 module has six pins, as described in the table below:
Pin
Name
Description
1
EN (Key)
Enables AT command mode when pulled HIGH. Defaults to LOW for normal operation.
2
VCC
Power supply input (3.3V to 5V).
3
GND
Ground connection.
4
TXD
Transmit data pin (connects to RX of microcontroller).
5
RXD
Receive data pin (connects to TX of microcontroller).
6
STATE
Indicates connection status (HIGH when connected, LOW when disconnected).
Usage Instructions
How to Use the HC-05 in a Circuit
Power Supply: Connect the VCC pin to a 3.3V or 5V power source and the GND pin to ground.
UART Communication: Connect the TXD pin of the HC-05 to the RX pin of your microcontroller, and the RXD pin of the HC-05 to the TX pin of your microcontroller. Use a voltage divider if your microcontroller operates at 5V logic levels to avoid damaging the RXD pin.
AT Command Mode: To configure the module, pull the EN (Key) pin HIGH and communicate with the module using AT commands via a serial terminal.
Normal Operation: Leave the EN (Key) pin LOW for standard Bluetooth communication.
Important Considerations and Best Practices
Voltage Levels: Ensure the RXD pin does not receive more than 3.3V. Use a voltage divider or level shifter if necessary.
Baud Rate: The default baud rate is 9600 bps. Ensure your microcontroller's UART settings match this value.
Connection Status: Use the STATE pin to monitor the connection status of the module.
Range: Keep the module within 10 meters of the paired device for optimal performance.
Example: Connecting HC-05 to Arduino UNO
Below is an example of how to use the HC-05 module with an Arduino UNO to send and receive data via Bluetooth.
Circuit Connections
HC-05 VCC → Arduino 5V
HC-05 GND → Arduino GND
HC-05 TXD → Arduino RX (Pin 0)
HC-05 RXD → Arduino TX (Pin 1) (use a voltage divider if needed)
Arduino Code
#include <SoftwareSerial.h>
// Define RX and TX pins for SoftwareSerial
SoftwareSerial BTSerial(10, 11); // RX = Pin 10, TX = Pin 11
void setup() {
Serial.begin(9600); // Initialize hardware serial for debugging
BTSerial.begin(9600); // Initialize Bluetooth serial communication
Serial.println("HC-05 Bluetooth Module Test");
Serial.println("Send data via Bluetooth to see it here.");
}
void loop() {
// Check if data is received from Bluetooth
if (BTSerial.available()) {
char data = BTSerial.read(); // Read data from HC-05
Serial.print("Received: ");
Serial.println(data); // Print received data to Serial Monitor
}
// Check if data is sent from Serial Monitor
if (Serial.available()) {
char data = Serial.read(); // Read data from Serial Monitor
BTSerial.write(data); // Send data to HC-05
Serial.print("Sent: ");
Serial.println(data); // Print sent data to Serial Monitor
}
}
Troubleshooting and FAQs
Common Issues and Solutions
Module Not Responding to AT Commands
Ensure the EN (Key) pin is pulled HIGH.
Verify the baud rate is set to 9600 bps (or the configured value).
Check the wiring and ensure the TX and RX pins are correctly connected.
Bluetooth Device Not Discoverable
Ensure the module is powered on and in pairing mode (LED blinking rapidly).
Check for interference from other devices operating in the 2.4 GHz range.
Data Transmission Issues
Verify the TX and RX connections between the HC-05 and the microcontroller.
Ensure the baud rate matches on both the HC-05 and the microcontroller.
Short Range or Unstable Connection
Ensure there are no physical obstructions or interference sources between the HC-05 and the paired device.
Check the power supply for stability.
FAQs
Q: Can the HC-05 module be used with 5V logic microcontrollers?
A: Yes, but you must use a voltage divider or level shifter for the RXD pin to avoid damage.
Q: How do I reset the HC-05 to factory settings?
A: Enter AT command mode and send the command AT+ORGL to reset the module to its default settings.
Q: Can the HC-05 connect to multiple devices simultaneously?
A: No, the HC-05 supports only one connection at a time.
Q: How do I change the module's name or PIN?
A: Use AT commands in command mode:
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