# Sixth Lichuang Electric Competition #Bluetooth 5.0 Desktop Amplifier

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* 1. Introduction to project functions

This is a small desktop power amplifier based on the KCX_BT003 Bluetooth 5.0 chip . The Bluetooth module comes with a wealth of peripheral modules: TF card, USB sound card, infrared remote control, Bluetooth call, AD button. Since there is no TF card and the computer does not support the typec interface, Therefore, the USB sound card and TF card modules have not been tested, but there should be no major problems. The power supply uses a PD decoy circuit. The output power of this amplifier is: 2X15W; so the speaker requirements: 4 ohms or 8 ohms, about 15W, and the speakers are not very Expensive, attached is a pair of Harman Kardon bought on Taobao for 17.2:

Power adapter requirements: supports PD15V3A protocol. Attached is a gallium nitride power adapter I picked up at the 80 block of a fish store. By the way, I want to check whether the power adapter supports the protocol. We can find out whether the power adapter output has PD protocol. Then find out whether it supports 15V3A.

The measured Bluetooth effective distance is about 10 meters, and a Bluetooth device name is attached.

The board has two audio input methods, AUX and Bluetooth. The audio input mode can be switched through the mode switch SW7. Here are a few pictures of the board.

This is a case made from a Jialichuang box. It can contain power adapters, data cables, and AUX audio cables. The copper pillars at the bottom of the board have been fixed with M3 screws. It is very compact and portable. After testing, the temperature of the internal components of the amplifier remains unchanged after long-term use. It’s not too high. In addition, TPA3130 drives a 2X15W speaker without a heat sink, so you don’t need to consider the heat dissipation of the single board. The shell is a bit crude and there are no professional tools hh. I will share the shell when I learn how to draw the shell in the future.

*2. Project attributes

The project is public for the first time and is original. It has not won any prize in other competitions and has not participated in any defense in school.

* 3. Open source agreement

GPL 3.0

*4. Hardware part

The Bluetooth module uses KCX_BT003 (part of the peripheral description of the Bluetooth module comes from the KCX_BT003 user manual), Bluetooth 5.0 protocol, and supports multiple functions. The Bluetooth module power supply uses an LC filter circuit to make the power supply purer. The filter circuit layout needs to be close to the module power supply lead. Pin, layout: Note that the inductor cannot be close to the antenna, and copper cannot be laid under the Bluetooth module antenna. It is best to use slotting, otherwise it may affect the sound quality and Bluetooth distance. Other peripheral circuits of the Bluetooth module are drawn with reference to the KCX_BT003 user manual, so some modules are I won’t introduce too much.

For the status indication part, I personally like to use a green LED for the power indicator, and the blue LED for the Bluetooth module to indicate the status. Turn on the power switch and the power indicator will work. If it does not work, please check whether the power supply is normal or whether the board is welded correctly.

Bluetooth instructions:

Pairing: LED flashes quickly (on and off for 250ms each)

MP3 playing: LED flashes slowly (on for 500ms and off for 500ms)

Pause state: LED is always on

Bluetooth playback: LED flashes twice every 2s

AD button detection module description:

VOL- key; short press: volume-, long press: volume continuous-

VOL+ key: short press: volume + long press: volume continuous +

PREV key: short press: previous song, long press: rewind

NEXT key: short press: next song, long press: fast forward

ON/OFF key: Short press to pause playback/double click to call back/long press to switch modes (when the U disk, TF card, and USBAUDIO are not online, only press this button in the dental cover mode without switching modes)

When a call comes in; short press to answer/long press to reject

During a call: Short press to hang up the current call

In Bluetooth mode: double-click to call back the last incoming call

In addition to Bluetooth audio input, this circuit also has AUX audio input. It uses a six-pin toggle switch to switch the input mode. The input mode selected by the switch direction has been marked with silk screen printing on the PCB.

In order to meet the desktop and convenient use of the power amplifier, the power input method adopts a PD decoy circuit. C10 is mainly used to eliminate the shutdown POP sound. R14 is to prevent the instantaneous current from breakdown of the MUTE pin of the power amplifier IC. R12 and R13 are used for subsequent upgrades of the power amplifier. It is reserved for power and debugging. Do not weld R12 and R13 , otherwise it may cause a short circuit or damage the op amp. The detailed function is attached to the screenshot of the manual in the picture below.

Since the two operational amplifier circuits are the same, I will omit the explanation. The preamplifier circuit uses high-performance and low-noise NE5532. I personally think that this operational amplifier is cost-effective. The adjustable resistors R21 and R23 can be adjusted according to the speaker power. Both of them can be replaced by potentiometers. If I like the compact design, I use an adjustable resistor. Refer to the NE5532 manual for the operational amplifier circuit. Since it is powered by a single power supply, a reference voltage is required. The 7.5V reference voltage uses a large capacitor and a The parallel connection of small capacitors makes the reference voltage more stable.

Finally, we have arrived at the most critical and last circuit. There may be a lot of nonsense. After consulting many forums, information and TI data manuals, we finally chose this TPA3130 as the rear output chip. Others were due to factors such as the need for dual power supplies or insufficient power. The fit is out. The speaker interface uses a VH3.96 connector, which is convenient for speaker replacement and storage.

*5. Software part

There is no software part involved in this circuit.

*6. BOM list

The BOM list of this project has been uploaded to the attachment. For C1, C14, C15, C16, and C17, I personally use nichicon 10UF BP stepless audio capacitors purchased from Xobao for audio coupling. You can choose the appropriate audio coupling capacitor according to personal preferences. Try changing the sound quality effect. If you have any questions, please leave a comment below and we will reply as soon as possible.

*7. Contest LOGO verification

Because the washing water is not used in some places or the washing water remains, the visual effect of the single board is affected.

* 8. Demonstrate your project and record it as a video for uploading

Video requirements: Please shoot horizontally, with a resolution of no less than 1280×720, in Mp4/Mov format, and the size of a single video is limited to 100M;

Video title: Lichuang Electric Competition: {Project Name}-{Video Module Name}; such as Lichuang Electric Competition: "Autonomous Driving" - Team Introduction.

More details: https://diy.szlcsc.com/posts/06c94d90c2c447dfbd9ed7339ff4a5b1