How to Use Hc 05: Examples, Pinouts, and Specs

The HC-05 is a versatile and powerful Bluetooth module that enables wireless communication between devices. It operates on Bluetooth 2.0 technology and can serve as both a master and a slave device. Common applications of the HC-05 include wireless control systems, serial communication, and remote data logging.

• Bluetooth Protocol: Bluetooth Specification v2.0+EDR
• Frequency: 2.4GHz ISM band
• Modulation: GFSK (Gaussian Frequency Shift Keying)
• Emission Power: ≤4dBm, Class 2
• Sensitivity: ≤-84dBm at 0.1% BER
• Speed: Asynchronous: 2.1Mbps(Max) / 160 kbps; Synchronous: 1Mbps/1Mbps
• Security: Authentication and encryption
• Profiles: Bluetooth serial port
• Operating Voltage: 3.3V (with 3.6V to 6V input voltage via onboard voltage regulator)
• Operating Current: 30mA (when paired and connected)
• Operating Temperature: -40°C to +105°C

1. Power Connections: Connect the VCC pin to a 5V supply, and the GND pin to the ground.
2. Data Connections: Connect the TXD pin of the HC-05 to the RXD pin of your microcontroller, and the RXD pin to the TXD pin.
3. Pairing Mode: To enter the pairing mode, power the HC-05 without setting the KEY pin high. The LED on the module will blink, indicating it's in pairing mode.
4. AT Command Mode: To configure the HC-05, set the KEY pin high upon power-up. This will allow you to send AT commands to the module for various settings.

• Use a voltage divider or a level shifter when connecting RXD to a 5V microcontroller to avoid damaging the HC-05's 3.3V logic.
• Ensure that the HC-05 is not in AT command mode during normal operation.
• Always disconnect the HC-05 from power before making or changing connections.

#include <SoftwareSerial.h>

SoftwareSerial BTSerial(10, 11); // RX | TX

void setup() {
  pinMode(9, OUTPUT);  // KEY pin if needed for AT commands
  digitalWrite(9, HIGH); // Enable AT command mode
  Serial.begin(9600);
  Serial.println("Enter AT commands:");
  BTSerial.begin(38400);  // HC-05 default speed in AT command mode
}

void loop() {
  // Keep reading from HC-05 and send to Arduino Serial Monitor
  if (BTSerial.available())
    Serial.write(BTSerial.read());

  // Keep reading from Arduino Serial Monitor and send to HC-05
  if (Serial.available())
    BTSerial.write(Serial.read());
}

• LED Not Blinking: Ensure the module is properly powered. Check the voltage at the VCC and GND pins.
• Cannot Pair: Make sure the device is in pairing mode and that the correct password (default is usually "1234" or "0000") is used.
• No Response to AT Commands: Confirm that the KEY pin is set high to enable AT command mode and that the baud rate matches the HC-05's default rate.

Q: How do I change the name or PIN of the HC-05 module? A: Enter AT command mode and use the commands AT+NAME=<newname> and AT+PIN=<newpin>.

Q: Can I use the HC-05 with a 3.3V microcontroller? A: Yes, the HC-05 operates at 3.3V logic levels, making it compatible with 3.3V systems.

Q: How can I check if my HC-05 is working? A: Power the HC-05 and use a smartphone with Bluetooth to search for new devices. The HC-05 should appear in the list of available devices.

Q: What is the range of the HC-05? A: The HC-05 is a Class 2 Bluetooth device, typically with a range of about 10 meters (30 feet) without obstructions.

Q: How do I reset the HC-05 to factory settings? A: Enter AT command mode and issue the AT+ORGL command.

This documentation provides a comprehensive guide to the HC-05 Bluetooth module, covering technical specifications, usage instructions, example code for Arduino UNO, and troubleshooting tips. For further assistance, consult the HC-05 datasheet or contact technical support.