DC isolated power supply for noise reduction: designed to be integrated with speakers, power amplifiers, and carmounted Bluetooth units to mitigate ground current noise and audible noise in the audio path, improving clarity and reducing hum. Dualdevice Bluetooth pairing: can connect two mobile phones simultaneously. After powering on, it automatically reconnects to the most recently paired device; to connect a second phone, you may need to select it in the phone's Bluetooth pairing list. Hands calling with low power consumption: uses the CSRA64215 platform for efficient operation. On powerup, the default volume is set to maximum, and hands calling is supported. Clear compatibility and applications: suitable for audio systems that require Bluetooth input, including speakers, power amplifiers, and car audio setups. Practical use scenarios: 1) Incar audio upgrade: integrate into the car stereo or amplifier to enable Bluetooth input with reduced ground noise, while allowing two family members to pair their phones. 2) Home DIY speaker project: add Bluetooth streaming and hands calling to a custom speaker or amplifier with minimal noise interference. 3) DIY audio electronics: use in projects requiring an isolated power supply and Bluetooth connectivity for reliable wireless audio and call functionality. Key performance attributes: DC isolation to minimize ground loop noise, CSRA64215 based lowpower Bluetooth solution, supports twodevice pairing, and immediate default volume behavior on powerup.