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HC-05 / HC-06 Bluetooth Serial Module | Master-Slave | 6-Pin / 4-Pin | Wireless UART Pass-Through | Arduino
HC-05 / HC-06 Bluetooth Serial Module | Master-Slave | 6-Pin / 4-Pin | Wireless UART Pass-Through | Arduino
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HC-05 / HC-06 Bluetooth Serial Module — Master-Slave | 6-Pin / 4-Pin | Wireless UART Pass-Through | Arduino
The HC-05 and HC-06 are the most widely used Bluetooth serial modules in the Arduino and embedded systems community — providing a simple, transparent UART-to-Bluetooth bridge that makes any serial device wireless without changing the application code. Data sent to the module’s UART TX/RX pins is transmitted wirelessly via Bluetooth 2.0 SPP (Serial Port Profile) to a paired device — a smartphone, PC, or another HC-05/HC-06 module. The key difference between the two: the HC-05 supports both master and slave modes (can initiate connections), while the HC-06 is slave-only (waits for connections). Both are configured via AT commands and operate at 5V with a -40°C to +85°C operating range.
Specifications
| Bluetooth Version | Bluetooth 2.0 + EDR (SPP) |
| Supply Voltage | 5V DC |
| Operating Temperature | -40°C to +85°C |
| Package | DIP (through-hole, breadboard compatible) |
| Interface | UART (TX, RX, VCC, GND) |
| Default Baud Rate | 9600 bps (configurable via AT commands) |
| Pairing PIN | 1234 (default, configurable) |
| Range | ~10 metres (Class 2) |
| Application | Wireless serial communication, Arduino wireless control |
| Origin | Mainland China |
HC-05 vs. HC-06 — Which to Choose
| Feature | HC-05 | HC-06 |
|---|---|---|
| Mode | Master + Slave (configurable) | Slave only |
| Can initiate connection | Yes (master mode) | No |
| Pins | 6-pin (includes EN/KEY and STATE) | 4-pin (TX, RX, VCC, GND) |
| AT command mode | Via KEY pin (hold HIGH at power-on) | Via baud rate change |
| Module-to-module | Yes (one master, one slave) | No (slave only) |
| Best for | Module-to-module wireless, master control | Smartphone/PC to Arduino wireless |
Pin Description (HC-05, 6-Pin)
| Pin | Function |
|---|---|
| VCC | Power supply (5V) |
| GND | Ground |
| TXD | UART transmit (connect to Arduino RX) |
| RXD | UART receive (connect to Arduino TX) |
| EN / KEY | AT command mode enable (hold HIGH at power-on) |
| STATE | Connection status indicator (HIGH = connected) |
Key Features
- ✅ Transparent UART bridge — no protocol changes needed, data passes through as-is
- ✅ HC-05 master+slave — can initiate connections to other Bluetooth devices (module-to-module wireless)
- ✅ HC-06 slave — simple slave-only operation for smartphone and PC wireless control
- ✅ AT command configuration — configure baud rate, device name, PIN, and mode via AT commands
- ✅ 5V supply — compatible with Arduino 5V systems (use voltage divider on RX for 3.3V systems)
- ✅ -40°C to +85°C — suitable for industrial and outdoor applications
- ✅ DIP package — breadboard and Dupont cable compatible
- ✅ ~10 metre range — adequate for most indoor wireless control applications
Common Applications
- Arduino wireless control via smartphone app (MIT App Inventor, Bluetooth Terminal)
- Wireless serial monitor for remote debugging
- Robot wireless control (HC-05 master on controller, HC-05 slave on robot)
- Wireless sensor data transmission to PC
- Bluetooth-controlled relay and switch
- Wireless data logger
- RC car and drone Bluetooth control
Arduino Wiring
- Connect HC-05/HC-06 VCC to Arduino 5V, GND to GND.
- Connect HC-05/HC-06 TXD to Arduino RX (pin 0 or SoftwareSerial RX pin).
- Connect HC-05/HC-06 RXD to Arduino TX via a voltage divider (1kΩ + 2kΩ) to reduce 5V TX to ~3.3V for the module RX.
- Pair the module with your smartphone (PIN: 1234 default).
- Use a Bluetooth terminal app to send and receive serial data.
Frequently Asked Questions
Q: Can I use HC-05/HC-06 with an ESP32 or Raspberry Pi?
A: Yes, but note that ESP32 and Raspberry Pi use 3.3V logic. The HC-05/HC-06 RX pin is 5V tolerant, but use a voltage divider or level shifter on the TX line from the module to the 3.3V device to be safe.
Q: What is the difference between “original” and “compatible” variants?
A: The “original” variant uses the genuine HC-05/HC-06 module with the original firmware. The “compatible” variant uses a compatible module with equivalent functionality at a lower price point.
Package Contents
- 1× HC-05 or HC-06 Bluetooth Serial Module (variant as selected)
