If you need to change the device name, baud rate, or enter configuration mode, you must use AT Commands.

How to enter AT Mode:

Common AT Commands:

| Command | Function | Example Response | | :--- | :--- | :--- | | AT | Test connection | OK | | AT+VERSION | Query firmware version | Version=... | | AT+NAMEyourname | Change BT Name | OK (Sets name to "yourname") | | AT+BAUD4 | Set Baud Rate | OK (4 = 9600, 5 = 19200, etc.) |

Best Practice Tips:

| JDY-40 Pin | Arduino Pin | Notes | | :--- | :--- | :--- | | VCC | 3.3V (Not 5V!) | Using 5V will eventually kill the module. | | GND | GND | Common ground is mandatory. | | TX | Pin 2 (SoftwareSerial) | Do not use hardware Serial (Pins 0/1) for data. | | RX | Pin 3 (SoftwareSerial) | Use a voltage divider (3.3V logic is safer). | | SET | Pin 4 (Optional) | Pull LOW to enter AT command mode. |

Critical Best Practice: Add a 100µF capacitor across VCC and GND on the JDY-40. This filters noise from the Arduino’s regulator and doubles the effective range.

The JDY-40 module provides a beginner-friendly way to add wireless serial communication to Arduino projects. With auto-pairing and transparent UART interface, a functional link can be implemented in less than 10 lines of code. Its limitations (half-duplex, moderate range) are acceptable for many educational and hobbyist applications.