#DebuggingRecord

[blevoice]

KT1025A BT201 Audio Bluetooth Module: Debugging Record of Bluetooth Audio Chip Recording Noise Issues

Recently, we received feedback from a Hungarian customer that there was a "buzzing/humming noise" when playing back recorded audio files (copied from the TF card to a computer) using the KT1025A BT201 test board. We collaborated with the client to debug and identify the issue, and finally solved it perfectly. Here is the record of the process.

Feedback

The customer reported the issue of "buzzing sound when playing audio files on a PC".

I. Restore the Customer's Test Scenario

Test Environment

The PC is connected to the KT1025 BT201 Module via the serial port to send operation instructions.

Insert the SD card into the Module to store the audio file.

The USB interface of the PC is connected to the Module's USB for power supply.

Test Steps

Use the serial port debugging tool on the PC to send commands for starting, pausing, and stopping the recording to the Module, and record a piece of sound.

Unplug the SD card from the Module and insert it into the PC.

Play the audio files on the SD card on the PC.

Test Result

There is a buzzing sound when playing audio files on the PC.

Other Attempts

Change the power supply mode of the module to battery power, disconnect the serial communication line, and shorten the microphone input at the same time. Similarly, there is a buzzing sound when the PC plays the recorded file.

II. Investigation Process

First, I conducted the test according to the above - mentioned method and recorded a video of the test process. The result was that there was no buzzing sound when playing the recorded file on the PC.

Test Peripheral Accessories and Tools

Mic (Model: XHXDZ - 4015, 4 * 1.5mm, 1.46KΩ, 1 - 10V, 150 - 500μA)

UartAssist V5.0.10 (BR:115200)

USB TO TTL (CH340G): For power supply and serial communication

III. Further Investigation in Collaboration with the Customer

Check the Power Supply

Based on the customer's findings:

1.Powering with 4 AA batteries results in a buzzing sound. 4 AA batteries (1.5V * 4) can reach 6V, which exceeds the specified power supply range.

2. Powering with 3 AA batteries eliminates the buzzing sound. 3 AA batteries (1.5V * 3) provide 4.5V, which is within the specified power supply range.

So, the root cause has been identified - the issue lies in the chip's power supply.

Design Principles Related to the Chip's Power Supply Voltage

The chip includes a built - in LDO that outputs 3.3V via PIN12, enabling it to power peripheral circuits, though this is not typically recommended.

Thanks to the built - in LDO, the chip supports a wide power supply voltage range, from as high as 5V (or even 5.2V) down to 3.2V, and can operate at a minimum of 2.9V in extreme cases.

Allowing up to 5V ensures redundancy and stability for the chip's internal 3.3V LDO supply while accommodating compatibility with peripheral circuits that may share the same power source.

Question 20 in the document "BT201_Frequently Asked Questions_FAQ_V3_Updated to 43" in the technical resources package for the 【KT1025A Bluetooth Chip】 also provides details about the chip's power supply specifications. A screenshot is included below.

By the way, our KT1025 BT201 Module has been sold in the domestic market of China for several years, with tens of thousands of shipments. I say this to tell you that you don't need to worry about its quality and reliability.

#BluetoothAudioChip #RecordingNoise #KT1025A #DebuggingRecord