Bl12-a3 | Bluetooth

One hidden feature of the BL12-A3 Bluetooth speaker is USB charge-out. You can plug your phone into the speaker’s USB-A port (using the speaker’s battery) for an emergency top-up. While the speaker’s 1800mAh battery won’t fully charge a modern smartphone, it adds 30-40% life—enough for critical calls.

// Simple Bluetooth echo example
void setup() 
  Serial.begin(9600);   // Monitor PC
  Serial1.begin(9600);  // BL12-A3 connected to Arduino’s Serial1 (pins 19(RX),18(TX) for Mega)
void loop() 
if (Serial1.available()) 
Serial.write(Serial1.read()); // Forward from BT to PC
if (Serial.available()) 
Serial1.write(Serial.read()); // Forward from PC to BT
 bl12-a3 bluetooth

Wiring for Arduino Uno:

Because it uses USB-C, you only need one cable for your phone, laptop, and the BL12-A3. The compact size (roughly 7 inches tall, 3 inches wide) fits in a water bottle holder. One hidden feature of the BL12-A3 Bluetooth speaker

The BL12-A3 acts as a wireless serial bridge. Any data sent via UART from your microcontroller is transmitted over Bluetooth to a paired device (e.g., smartphone, PC, or another BL12-A3). Similarly, data received via Bluetooth is output through the TX pin. Wiring for Arduino Uno: Because it uses USB-C,