Introduction: Through the transformation of a small Bluetooth speaker, it becomes an audio signal source. Provides signals for ultrasonic directional transmission of sound. After testing, it is found that it is necessary to introduce an RC low-pass filter into the original 555 modulated signal input port to avoid the oscillation of the signal transmission system.
关键词: Bluetooth speaker , ultrasonic
§ 01 Bluetooth Speaker
1.1 Background introduction
After building MX1919-based ultrasonic array driver board , in order to be able to demonstrate in the classroom, it is necessary to make a live sound source. So I transformed a small bluetooth speaker at hand. The relevant audio information will be broadcast live in the classroom at that time.
▲ 图1.1.1 改造后的蓝牙小音箱
When the external Bluetooth audio output is connected to the circuit, the circuit stops working. By introducing an RC low-pass filter circuit at the audio input, the problem is solved.
▲ 图1.1.2 在接口电路需要增加低通滤波器
The transformation process is recorded below.
1.2 APPLE Script
| Background brief | Image | Note |
|---|---|---|
| Continuing from the book above, the ultrasonic transmitter array was previously made for classroom demonstrations, and now a signal source that can output audio in the field is required. |  |
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| Now I have a small bluetooth speaker at hand, |  |
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| This speaker now has no external headphone jack and needs to be reworked. |  |
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| It is disassembled below and the headphone jack is added. |  |
| Removing the Small Bluetooth Speaker | Image | Note |
|---|---|---|
| From the appearance of the speaker, there are no disassembly screw holes. |  |
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| Remove the upper sealing plastic ring, and you can see the three fixing screw holes above. |  |
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| Use a screwdriver to loosen the three screw holes. |  |
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| This is the internal structure of the small stereo after disassembly, and now the speaker interface has been disconnected from the circuit board. Now it is necessary to recreate an intermediate interface between these two interfaces to drive the external ultrasonic array board. |  |
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| Open a hole in the speaker housing | Image | Note |
|---|---|---|
| Prepare to route the speaker leads out of the speaker enclosure, |  |
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| Make a temporary interface with the outside of the plug. |  |
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| The first step is to open a hole in the casing. |  |
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| This cavity is about 4mm in diameter and width. |  |
| Take the speaker wire out | Image | Note |
|---|---|---|
| First solder the output leads of the audio amplifier board. |  |
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| Now lead the bluetooth amplifier output out of the case. |  |
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| The speaker leads are also soldered out below. |  |
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| In this way, the leads of the speaker are also led out of the casing. |  |
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| They can be connected outside the case. Prepare another interface for connecting the ultrasonic modulation board. |  |
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| But the bluetooth case is re-fixed and restored to its original state. |  |
| test | Image | Note |
|---|---|---|
| First test the Bluetooth speaker function. Connect the output of the amplifier board to its own speakers. |  |
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| Use your phone to test the speaker output for music. |  |
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| Then use the external cable to input the bluetooth audio to the ultrasonic array 555 modulation port, |  |
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| However, the operating current of the circuit suddenly decreased by about 20mA, which is suspected to be an interference signal. |  |
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| So at the input end, an RC low-pass filter circuit is introduced, and the problem is solved. |  |
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| Now the ultrasonic delivery system for classroom demonstrations is finally complete. |  |
※ Summary ※
Through the transformation of the small bluetooth speaker, it becomes an audio signal source. Provides signals for ultrasonic directional transmission of sound. After testing, it is found that it is necessary to introduce an RC low-pass filter into the original 555 modulated signal input port to avoid the oscillation of the signal transmission system.
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