| Pin # | Name | Type | Function (Full Description) | | :--- | :--- | :--- | :--- | | 1 | VCC | Power | 3.3V DC input. Do not exceed 3.6V | | 2 | GND | Ground | System ground | | 3 | UART_TX | Output | Serial data transmit (3.3V logic) | | 4 | UART_RX | Input | Serial data receive (3.3V logic) | | 5 | RTS | Output | Request to Send (hardware flow control) | | 6 | CTS | Input | Clear to Send | | 7 | RESET | Input | Active-low hardware reset (pull high through 10k resistor) | | 8 | STATUS | Output | LED indicator (blinks on connection) | | 9 | PCM_CLK | I/O | Pulse-code modulation clock (for digital audio) | | 10 | PCM_SYNC | I/O | PCM frame sync | | 11 | PCM_IN | Input | PCM data input from codec | | 12 | PCM_OUT | Output | PCM data output to codec | | 13 | GPIO0 | I/O | Configurable – often used for pairing button | | 14 | GPIO1 | I/O | Configurable – used for mute or LED | | 15 | GPIO2 | I/O | Configurable – power control | | 16 | USB_DP | I/O | Direct USB 2.0 D+ (optional – not always populated) | | 17 | USB_DN | I/O | Direct USB 2.0 D- | | 18 | ANT | RF | Antenna output (if external antenna needed) | | 19 | NC | – | No connect | | 20 | GND | Ground | Secondary ground plane |
The UART pins operate at 3.3V logic . Connecting them directly to 5V (e.g., an Arduino Uno's RX/TX) without a level shifter will permanently destroy the BL12A3. 4. Full Communication Protocol (AT Command Set) Unlike modern BLE modules that use complex GATT profiles, the BL12A3 uses a legacy AT command set over UART. Once powered on, the module defaults to 115200 baud, 8 data bits, 1 stop bit, no parity. bl12a3 bluetooth full
| Command | Function | Full Response Example | | :--- | :--- | :--- | | AT+NAME=<text> | Set device name | +NAME: "BL12A3_Audio" | | AT+ADDR? | Query MAC address | +ADDR: 00:1A:7D:DA:71:0A | | AT+ROLE=M | Set as Master | OK | | AT+ROLE=S | Set as Slave (default) | OK | | AT+CONN=<MAC> | Connect to specific device | +CONN: SUCCESS or +CONN: FAIL | | AT+DISC | Disconnect current link | OK | | AT+UART=<baud>,<stop>,<parity> | Change UART settings | Examples: AT+UART=9600,1,0 | | AT+AUTH=<0/1> | Enable/disable pairing authentication | AT+AUTH=1 (enable PIN) | | AT+PIN=<code> | Set pairing PIN (default 0000) | AT+PIN=1234 | | AT+RESTORE | Factory reset (full nvram clear) | OK (module reboots) | | Pin # | Name | Type |
If you are repairing a vintage Bluetooth speaker or building a wireless serial bridge where audio quality matters more than power consumption, the BL12A3—with its feature set of A2DP, HFP, and SPP—is a robust, proven workhorse. | Command | Function | Full Response Example
This article provides a complete, technical breakdown of the BL12A3 Bluetooth module—its architecture, pinout, programming specifications, real-world applications, and troubleshooting tips. Whether you are integrating it into a PCB design or troubleshooting a faulty connection in a consumer device, this guide covers the specification set. 1. Introduction: Decoding the BL12A3 The BL12A3 is not a consumer-grade USB dongle; rather, it is an embedded HCI (Host Controller Interface) Bluetooth module commonly found in legacy portable speakers, wireless headsets, and automotive hands-free kits. The "BL" prefix typically denotes a Broadcom (now acquired by Cypress/Infineon) or a licensed compatible chipset, while "12A3" refers to a specific firmware and hardware revision.
Always verify the voltage (3.3V only!), confirm the PCM pinout for audio, and use a AT+RESTORE before deployment to clear any latent OEM customizations. Have a specific BL12A3 question not covered here? Check the legacy Broadcom forums or use a USB logic analyzer to capture the full boot-up sequence from your device.