The Taotronics Bluetooth Speaker
Opening It Up!
Opening this Bluetooth speaker wasn’t very easy. This speaker employed an interesting construction method of melting plastic over the perforated speaker grills.
Melted Plastic Construction
The melted plastic was scraped away using a flat hobby-knife. Once the melted plastic was removed the speaker grills lifted right off. Once the speaker grills were off a few standard Phillips screws held the plastic enclosure together. The screws were removed and the enclosure was separated.
The Opened Bluetooth Speaker
The major component of any Bluetooth speaker is the speaker! In this case, there are two speakers that are rated at 3W each.
One of the 3-watt speakers
This speaker has a listed battery life of 8 to 10 hours. The battery this speaker uses shows the part number 623450. The number represents a battery that is 6.2mm high, 34mm wide, and 50mm tall. Lithium batteries like these often are made by different manufacturers in similar sized packages, a quick Google search of “623450 battery” leads to many different manufacturers.
The 1000mAh Li-Ion Battery
This battery also contains a small circuit board. This small board acts as protection circuitry for the battery. These circuit boards often offer protection from short circuits, over discharge, over-current, and over-charge voltage.
The Battery Protection PCB
Primary Circuit Board
The primary circuit board in this Bluetooth speaker handles all the functions of the speaker. This circuit board is laid out into sections for battery charging, voltage regulation, audio amplification, and Bluetooth.
The Primary Circuit Board
On the rear of the primary circuit board, there isn’t a lot.
The Sparce Rear of the Primary Circuit Board
There is a microphone for making voice calls and 3 push buttons for volume up, volume down, and play/pause control.
The Control Push Buttons
The Charging Circuitry
The first section that we're going to take a look at is the charging section. The charging is handled by a Linear Technology LTC4054. The IC is an SOT-23-5 package and requires minimal external components. One of the exterior components required though is a resistor to set the charge current. In the case of this circuit board, the resistor is a 2k ohm resistor labeled R19. This value sets the LTC4054 charge rate to 500mA. With the speaker’s battery having a rating of 1000mAh, it will take about 2 hours to charge. In addition, this section of the power supply uses two AO3401 MOSFETS to switch between the Lithium battery or the USB power supply if the Bluetooth speaker is charging.
The Power Supply Circuitry
Moving to the right on the circuit board we reach the power supply section. This section is comprised of typically boost regular set up. At the heart of the power supply is a boost converter made by LPS (Low Power Semiconductor) part number LP6212. This is a fairly typically boost converter that can supply 6A of power.
The Boost Converter
The boost converter requires an inductor, diode, input and output capacitors; and resistors to form a voltage divider for the voltage feedback mechanism. The circuit used on this board is very similar to the typical application circuit displayed in the datasheet except with large capacitors.
The Example Circuit From the Datasheet
The Circuitry for the Audio
The next section of electronics contains all of the electronics for controlling the two speakers. There are two main components in this section, the first is the audio amplifier. The audio amplifier is part number HT6818 made by Jiaxing Heroic Electronic Technology. This audio amplifier is a stereo amplifier that supports two outputs up to 3.3W.
The Amplifier for the Speakers
The second major component located in this section is an NJRC NJM14558M op-amp.
The 4558 Op-Amp
The Bluetooth Circuitry
The last major section of this circuit board is the Bluetooth section. The main component of the Bluetooth section is a CSR8635 Bluetooth system. This IC, made by CSR, is intended to be used wireless audio products just like this Bluetooth speaker. This Bluetooth module supports Bluetooth 4.0, wireless stereo audio, wired-in audio, ect. The Bluetooth IC even contains voltage regulators and a lithium battery charger that isn’t used in this product. Paired with the Bluetooth module is an FM24C128 128K-bit EEPROM made by Fairchild. This communicates to the Bluetooth module over a two wire serial interface and most likely contains information about the settings and configuration of the Bluetooth module. The last major component of the Bluetooth section is the antenna. This module uses a trace antenna that used to send and receive the data. There are two inductors, L6 and L4, that are used to fine tune the impedance of the antenna for optimal performance.
The Trace Antenna
Secondary Circuit Board
The Secondary Circuit Board
There's another small circuit board located inside the speaker. The small board is used to connect the audio line-in, USB power, and the power button to the primary circuit board. An interesting note is that the secondary board contains two LEDs that are not visible from the outside of the speaker.
Wrapping it up!
Bluetooth speakers like these don’t cost a lot of money, typically around $20 to $30, but still manage to pack a number of components inside of them and possess a reasonably high build quality. (The speaker was even FCC certified!)
All the Parts of the Bluetooth Speaker
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