Bluetooth Module (HC-05) Symbol
Definition: The Bluetooth Module (HC-05) symbol represents a serial-to-Bluetooth bridge IC module used in circuit diagrams to show a wireless communication peripheral that translates UART serial data to Bluetooth 2.0 Classic RF signals operating at 2.4 GHz, commonly depicted as a rectangular block with VCC, GND, TXD, RXD, and STATE pins.
Also known as: HC-05 module, Bluetooth serial module, BT module, wireless UART module, HC-06, serial Bluetooth adapter.
What the Bluetooth Module (HC-05) symbol means
The Bluetooth Module (HC-05) symbol marks the location of a small PCB-mounted module containing a Bluetooth SoC (typically CSR BC417 or equivalent) that provides wireless serial communication between a microcontroller and a Bluetooth-capable device such as a smartphone, PC, or another microcontroller. In wiring diagrams the module appears as a labelled rectangle with its key interface pins: VCC (3.3–5 V power), GND (ground), TXD (module transmit data out), RXD (module receive data in), and STATE (link status indicator).
The HC-05 module is specifically a master/slave configurable Bluetooth 2.0 + EDR (Enhanced Data Rate) module, while the HC-06 is a slave-only variant. Both operate over a standard UART interface at configurable baud rates (default 9600 baud) and are widely used in robotics, Arduino projects, and IoT prototyping. The symbol helps designers plan UART level shifting (the HC-05 RXD pin is 3.3 V tolerant, not 5 V), power supply routing, and antenna clearance.
How to identify the Bluetooth Module (HC-05) symbol
The Bluetooth Module symbol is drawn as a rectangle labelled 'BT MODULE' or 'HC-05' with five pins along the bottom edge: VCC, GND, TXD, RXD, and STATE (from left to right). Some diagrams add a small antenna icon or Bluetooth logo inside the rectangle. The module outline may also show a KEY/EN pin used for AT command mode on HC-05 boards.
Function and usage boundary
The HC-05 Bluetooth module receives serial UART bytes on its RXD pin from a host microcontroller and wirelessly transmits them to a paired Bluetooth device; it simultaneously receives Bluetooth RF data and forwards it as UART bytes on its TXD pin to the host. Baud rate, device name, PIN code, and master/slave role are configured via AT commands sent over the UART when the KEY pin is held high. The STATE pin outputs a pulsed signal when searching for a connection and a steady high signal when connected.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 does not define a specific Bluetooth module symbol. In IEC-compliant block diagrams, the module is shown as a rectangle with a communication-function qualifier and the label 'BT' or 'Bluetooth' per IEC 60617-02 (signal sources and signal processing) general-purpose block conventions. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 does not define a Bluetooth module symbol. North American schematics use a labelled rectangular block. The IEEE 802.15.1 standard governs the Bluetooth protocol itself, not the schematic symbol. |
| Key difference | No standardised unique glyph exists in IEC 60617 or ANSI Y32.2 for a Bluetooth module; both conventions use a labelled rectangle. The Bluetooth logo (a stylised 'B' rune) is sometimes added inside the block for clarity but is a trademark symbol, not a standards-defined glyph. |
The displayed SVG is the live editor implementation, not a licensed reproduction or certification of an IEC or IEEE database glyph. Verify the exact official entry and project edition before issuing work.
Logical terminals
| Logical ID | Editor terminal name |
|---|---|
| vcc | VCC |
| gnd | GND |
| txd | TXD |
| rxd | RXD |
| state | STATE |
Where the Bluetooth Module (HC-05) symbol is used
- Arduino and microcontroller projects requiring wireless UART communication with a smartphone app for data logging or remote control
- Robotics platforms that receive Bluetooth joystick or phone-app commands to control motors and servos wirelessly
- DIY IoT sensors that transmit temperature, humidity, or other sensor data to a PC or phone over Bluetooth serial
- Wireless firmware debugging and serial monitor replacement — replacing the USB cable with a Bluetooth link during embedded development
- Home automation prototypes where Bluetooth serial bridges relay commands between a microcontroller and a central hub
- Educational electronics kits demonstrating wireless communication principles in STEM curricula
Key facts
- The HC-05 Bluetooth module symbol represents a Bluetooth 2.0 + EDR serial bridge that communicates with a host microcontroller over UART using pins TXD (module TX), RXD (module RX), VCC, GND, and STATE.
- The HC-05 RXD pin is 3.3 V logic — a voltage divider or level shifter is required when connecting to a 5 V microcontroller UART TX to avoid damaging the module.
- Default UART settings are 9600 baud, 8N1; AT command mode (accessed by holding the KEY pin HIGH at power-up) allows changing baud rate, device name, PIN code, and master/slave role.
- The HC-05 can act as Bluetooth master or slave; the HC-06 is slave-only — this role difference is not visible from the schematic symbol and must be noted in the part label.
- Operating frequency is 2.4–2.485 GHz in the ISM band; the antenna requires at least 3 cm clearance from metal objects for reliable range.
- Supply current during active Bluetooth connection is approximately 35–40 mA; designers must include a 100 µF decoupling capacitor near the VCC pin to handle RF burst current demands.
- IEEE 802.15.1 (derived from Bluetooth SIG core specification) governs the Bluetooth protocol; the schematic symbol is based on general rectangular block conventions per IEC 60617-02 and ANSI Y32.2.
Frequently asked questions
What does the Bluetooth module HC-05 symbol look like in a circuit diagram?
The HC-05 Bluetooth module symbol is a rectangle labelled 'BT MODULE' or 'HC-05' with pins along the bottom: VCC (power), GND (ground), TXD (transmit out), RXD (receive in), and STATE (connection status). Some diagrams include a small Bluetooth antenna icon inside the block. No unique standardised IEC or ANSI glyph exists; a labelled rectangle is universally used.
What does the Bluetooth module symbol mean on a schematic?
The symbol indicates the presence of a serial-to-Bluetooth wireless bridge module. It tells the designer that a UART interface (TXD/RXD) connects the host microcontroller to the module, which wirelessly pairs with smartphones, PCs, or other Bluetooth devices. The VCC and GND pins must receive stable 3.3–5 V supply with adequate current (35–40 mA).
What are the pins on the HC-05 Bluetooth module symbol?
The five main pins shown in the schematic symbol are VCC (3.3–5 V supply), GND (ground), TXD (module transmit output, connect to host RX), RXD (module receive input, connect to host TX via 3.3 V level shifter), and STATE (open-drain status output: pulsing = searching, steady HIGH = connected). A KEY or EN pin enables AT command configuration mode.
Do I need a level shifter for the HC-05 with an Arduino?
Yes. The HC-05 RXD pin is 3.3 V tolerant; connecting a 5 V Arduino TX signal directly will damage the module over time. A simple resistor voltage divider (1 kΩ series + 2 kΩ to GND) reduces the 5 V signal to ~3.3 V. The HC-05 TXD output is 3.3 V, which most 5 V microcontrollers read as a valid logic HIGH without modification.
What is the difference between HC-05 and HC-06 Bluetooth modules?
The HC-05 can operate as either Bluetooth master or slave and has an AT command mode accessible via the KEY pin, making it suitable for creating Bluetooth connections to other devices. The HC-06 is slave-only and has a simpler AT command interface. Both use the same UART serial interface and share a similar schematic symbol, differentiated by the part label.
What standard defines the Bluetooth protocol used by the HC-05 module?
The Bluetooth Classic protocol (version 2.0 + EDR) is governed by IEEE 802.15.1, which is derived from the Bluetooth Special Interest Group (SIG) core specification. The operating frequency is 2.4–2.485 GHz ISM band. The HC-05 module supports Serial Port Profile (SPP), the Bluetooth profile that emulates a serial cable connection.
What is the maximum range of an HC-05 Bluetooth module?
HC-05 modules are typically Bluetooth Class 2 devices with a nominal range of up to 10 metres in open air with no obstructions. Class 1 variants rated to 100 m also exist but are less common. In practice, walls, RF interference, and antenna orientation reduce effective range to 5–8 m indoors.
Related symbols
- Antenna symbol
- ESP32 symbol
- LoRa Module symbol
- nRF24L01 RF Module symbol
- Resistor symbol
- Shift Register (8-bit) symbol
Physical breadboard, PCB, and panel mapping
No universal physical profile is published for this symbol yet. Create a versioned custom part from the exact manufacturer dimensions and terminal map before fabrication.
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