Winter Warm Heart Box

I. Function Description:
After plugging in the power, the default startup mode is music mode. Pre-store desired songs on the memory card. Insert the memory card, press the first button to start playing songs, the second button is for previous track/volume down (press once to skip to the previous track, press and hold volume down), the third button is for next track/volume up, and the fourth button starts/stops recording. When a memory card is present, recordings are stored on the SD card; otherwise, they are stored in external FLASH memory. I have also brought out the chip's serial port, allowing various functions to be achieved by sending commands to the chip via a microcontroller or other modules.
II. Schematic Design Description:
This is the SD card
circuit. I used a 24MHz crystal oscillator and a 4-pin
N8900 main control circuit. I designed a Bluetooth onboard antenna and an FM port.
I used an 8002A power amplifier chip to amplify the signal.
I used Type-C for power supply, mainly because this type of charger is becoming increasingly common, and other types are less suitable. Of course, I also have a serial port and a USB port, which can also provide power.
This is the microphone circuit;
I won't go into detail about the others, you can refer to the project files.
III. PCB Design Description:
This mainly concerns the Bluetooth antenna. I revised it twice, and this is the final version. Fortunately, it works.
I didn't do copper plating on the entire PCB because I tested it once after doing so and found that the sound quality became very poor.
IV. Software Description:
This is ready to use as soon as it's soldered; no program download is required. However, it has serial communication functionality, so those familiar with microcontrollers can control it.
V. Physical Demonstration:
It looks pretty good. The back is nice, and I used a colored finish
. I soldered the microphone on the back. During installation, I found that the outer shell wouldn't install, so I had to use needle-nose pliers to cut off a portion and then apply glue. It's not noticeable unless you look closely. The panel design is also good; it fits perfectly.
Here is the final product. It looks pretty good; I personally think it's quite beautiful and compact. Note that if you want to use it, it's best to design your own outer shell. Mine is too cheap.
VI. Precautions:
The panel, colored silkscreen, and 3D shell can all be designed by yourself, but it's best to design a new 3D shell. Chips were sold on Taobao, but they're no longer available and probably out of stock. Other items can be bought at LCSC Mall and are more affordable.