Homemade chassis 12x12cm fan position speaker (supports USB decoding)

The chips used
are still considering using PCM2912A USB decoding chip and NS4225 dual-channel amplifier. Why not use I2S DAC? Because I am too lazy to design it. The DAC that comes with PCM2912A is pretty good, better than the one that comes with PCM2706. NS4225 is very cheap now. Then pay attention to not buying polished chips of PCM2912A, which will not be used for a long time; PCM2912A needs to be configured through a resistor network. I also did some processing on the differential input of NS4225 to support single-ended input.
The speaker part and the installation
use the speakers of Samsung TV, 10W 6Ω, which is not expensive, and the sound is quite loud.
Tip: pay attention to the installation polarity of the speaker! (Especially important! Please consult the seller to distinguish the polarity)
Next are the parts needed to fix the speaker on the board: double-pass round brass column M3*4, flat head screw M3*16, double-pass hexagonal brass column M3*4.
The double-pass round brass column is mainly responsible for the electrical connection between the speaker and the board. It must be tightened to ensure good contact. The flat head screw and double-pass hexagonal brass column play a fixing role. You can see my real photos or videos here. It is best to tighten two hexagonal brass columns together to prevent loosening! ! !
Schematic design description
In fact, I have retained the full set of functions of this part of the PCM2912A circuit, and the microphone function is also retained. If you want to do something else, just delete the power amplifier part.
First of all, the configuration circuit of PCM2912A is as follows:
Here you can see a bunch of 0 ohm resistors, but the actual configuration of the POWER and MAMP pins only allows one level to be turned on at the same time! VCCP is the high level 3.3V provided by the chip. Don't connect all of them to GND directly with 0 ohm resistors. Only one of GND and VCCP is allowed to happen, not at the same time! ! (Again, it must be a one-or-the-other connection! !); POWER is the power consumption determination pin. The chip current limit is 100mA when the level is low, and the chip current limit is 500mA when the level is high. Adjust according to the situation; MAMP pin is the microphone preamplifier gain control. The preamplifier is turned off when the level is low, and the preamplifier is turned on +20 dB when the level is high. Configure according to the needs.
If the microphone function is not needed, the circuit shown in the following figure needs to be modified:
it is best to solder 0 ohm resistors to R12 and R14 of the circuit, and D3, D4, buttons and MIC1 do not need to be soldered, so that the microphone function can be disabled.
Attention! ! Attention! ! If you need to use the microphone function, please do not solder R12 and R14 0 ohm resistors, and complete the circuits in the above two figures! ! (Key points!!)
The configuration circuit of NS4225 is as follows:
Here PBTL is the setting of the amplifier operation mode, we just need to connect it to the ground directly; Similarly, the /SD pin of the chip is the enable pin of the chip, and the low level means it is off. Here, the circuit is still a two-choice connection. Connecting VCCP means it is normally open, and some small noise may occur; if SSPND is connected, NS4225 will be turned on only when PCM2912A has an audio signal to transmit, which can avoid the situation of small noise when it is not working, but, but!! When some computers start and shut down, they will send a verification message to PCM2912A, and then PCM2912A will process it and send it to NS4225, so there will be a puff sound, which is normal!! This is a problem with the chip itself.
The voltage configuration of the step-down module is as follows:
Here I have left a R20 three-pin sliding rheostat and an R27 chip resistor, but I still recommend that you use the chip resistor to configure the voltage after calculation, because the sliding rheostat may cause a certain change in resistance due to vibration or aging factors; Here comes the key point! ! Here comes the point! ! The circuit I chose here is LM2576S-5.0, the feedback pin is directly connected to the output for 5V step-down, and it is adjusted here, so the output voltage of this circuit is determined by resistors R27 and R50, Vout = [5x(R50 + R27)] / R50, here I use 10V voltage so R27 is 1K ohm, and R20 is calculated in the same way. Later I added a lot of capacitors and a linear regulator in series to ensure that the voltage after step-down is stable enough. The computer power input interface uses a large 4PIN, and the 5V power supply also uses a large 4PIN. Do not use USB power supply to ensure sufficient power. Some motherboards USB2.0 current can't run more than 500mA.
USB transfer instructions: (Emphasis!! Emphasis!!)
If you want to connect to the USB2.0 interface of the motherboard, then buy a nine-pin USB connector and make a XH2.54 4PIN terminal at the other end according to the interface order of the board. You will know it by looking at the physical picture; if you want to connect to the USB interface, use a USB cable to cut the four wires inside and make a XH2.54 4PIN terminal according to the interface order of the board!
PCB design instructions
Here I divided the GND into three pieces, all of which were isolated in different ways, and I hollowed out the bottom of the inductor to prevent the magnetic field from affecting the GND when the inductor works at high frequency. Although there is a shielding cover, I still feel relieved to dig it out. The board in the PCB picture is the board I corrected the error, and the physical picture is my first generation of problematic board, which may look different. In addition, you need to pay attention to the voltage resistance of the capacitor used! ! It is best to choose a capacitor with a high voltage resistance connected to the speaker! ! The link of the demonstration video
of the actual display is: https://www.bilibili.com/video/BV1b14y1M7sa/ The sound quality of the video may be a little compressed. In addition, the noise in the video all comes from my chair. The sound quality and loudness are still good. You can take a closer look at how to install it.