HC-05 Bluetooth Module Pinout

Overview

The HC-05 is a serial Bluetooth module built for transparent wireless serial communication, it acts as a cable replacement, letting a microcontroller send and receive data over Bluetooth using plain UART. It comes in two formats: the bare module, exposing all 34 pins for custom PCB designs, and the breakout board, which simplifies things down to 6 pins for prototyping.

Getting started

Check your specific breakout board’s VCC rating before powering it, some accept 5V thanks to an onboard regulator, others need 3.3V directly onto the bare module.

Hello World: talk to it over serial

The HC-05 equivalent of “Hello World”: send AT commands over a software serial port and read the module’s replies. Hold EN/KEY high while powering on to enter AT command mode first.

#include <SoftwareSerial.h>

SoftwareSerial bt(2, 3); // RX, TX
void setup() {
  Serial.begin(9600);
  bt.begin(38400); // AT command mode baud rate  bt.println("AT");
}

void loop() {
  if (bt.available()) Serial.write(bt.read());
  if (Serial.available()) bt.write(Serial.read());
}

Open the Serial Monitor at 9600 baud, you should see “OK” back from the module. AT command mode uses 38400 baud by default, normal communication mode uses whatever baud rate you last configured (9600 out of the box).

Breakout board pins

The 6 pins exposed on almost every HC-05 breakout board, this is what most people actually wire up.

Bare module pinout diagram

For anyone designing their own PCB around the bare 34-pin module rather than using a breakout board.

Dimensions

The bare module (13 by 27 mm, 28 castellated pads at 1.27 mm pitch) alongside the common breakout board it usually ships on (15 by 37 mm, 6-pin header at 2.54 mm pitch, with the onboard pairing button).

34-pin reference

Most projects only ever need the 6 breakout pins above, this table is for the bare module.

Safety notes