QCC303X Bluetooth Receiver

   Basic overview:   
          This Bluetooth receiver uses the BTM334 Bluetooth module, uses the module's I2S as audio output, and uses TI's PCM5121 for DAC, which supports USB sound card function.
      The block diagram of the Bluetooth receiver is as follows: Specific details:
        The chip used in the Bluetooth module is Qualcomm's QCC3034, which supports ordinary SBC, AAC encoding, and also supports Qualcomm's own aptX, aptX-HD, aptX-LL encoding, ensuring the quality of Bluetooth audio; it can also be connected to a computer via USB as a USB sound card, driver-free, and supports up to 16bit/48k. The DAC (digital-to-analog converter) uses a PCM5121 from TI (Texas Instruments), which features a built-in charge pump to generate a negative power supply, can achieve output without coupling, supports hard control/SPI/I2C, has fixed audio processing functions, supports up to 32bit/384k, 2VRMS output, and personally feels good. (But I only used H/W Mode, wasting most of the functions of this chip, what a pity) Two LDOs are used for power supply. AZ1117 is responsible for part of the power supply of the Bluetooth module, and ME6211, a high-speed and high-PSRR LDO, is responsible for the power supply of the DAC to ensure the purity of the DAC power supply. The USB interface uses an extremely convenient type-c, and you can choose between power supply only and power supply + USB sound card function according to the insertion direction (Note: If the receiver is already connected to the computer and the Bluetooth is connected to the mobile phone, you need to press and hold the Play/Pause key for a few seconds to disconnect the Bluetooth connection to enable the USB sound card function). There are 3 touch switches on the board, and the functions are play/pause, previous song/volume-, next song/volume+. Long press the play key to cut off the Bluetooth connection. The board also reserves an I2S interface (lead out through the ZH1.5-5pin connector, see the schematic diagram for definition).
Connecting a computer
to a mobile phone
About listening/sound quality:
        almost no bottom noise, clear sound, high resolution, no dragging, better than the CODEC built into the computer/mobile phone, quite touching.
Problems/improvements encountered during production:
        1. The definition of the headphone socket was a trap, resulting in only the left channel sounding. I had to do a small operation on the board and fly a wire to the right channel of the headphone socket. After the wire was flown, the sound of the left and right channels was normal.
The modified schematic diagram of the headphone interface is as follows:
         2. In addition to PCM512x (PCM5121, 5122), the DAC chip can also be PCM510xA (such as PCM5102A). The latter has the same functions except that it does not have SPI, I2C, and DSP. When soldering, the pin1 of PCM510xA should be aligned with the pad pointed to by the triangle on the PCB (that is, the pin1 of PCM512x and PCM510xA).
         3. In addition to BTM334, the Bluetooth module can also be replaced with the following modules, which are completely pin-to-pin, except that there are differences in some functions.
Link: http://www.tianjiarun.com/post/40.html
 
*The datasheet and other reference materials used in the design of this Bluetooth receiver will be placed in the attachment