There are only main parts to this circuit: Audio amplifier circuit, Bluetooth module, and charging module.
1) Charging module:
The TP4056 acts as the charging module, and it is connected to the rechargeable battery through B+ and B-. The output pins on the charging module (OUT+ and OUT-) are connected to the Vcc and ground pins of the Bluetooth and audio amplifier module. This is how the circuit is powered.
Since the glasses are cordless, they will have to have a rechargeable battery in them, and hence, an appropriate circuit to charge and discharge the battery safely is also required, which is what the TP4056 does.
The board then changes the current and voltage to optimize charging up the battery. There is also a protection feature in the TP4056 board that prevents the rechargeable battery’s voltage from becoming too high or too low.
Here is a good video explanation: link.
2) Bluetooth Audio module:
The Bluetooth module allows your device (phone/laptop/tablet) to connect wirelessly to the glasses through Bluetooth.
It has a Vcc and ground pin for power and 3 output pins corresponding to the left earphone, right earphone, and ground. These three pins are connected to the audio amplifier for the signal to be amplified and usable for earphones.
Once the Bluetooth audio module is powered up, it should appear on your phone’s Bluetooth scanner as 3.0 BT or VIRE BT.
3) Audio amplifier:
The PAM8403 board is perhaps the cheapest and most effective audio amplifier board out there. It has three input pins that are connected to the Bluetoothmodule’s three output pins. It also has 4 output pins, two for each speaker/earphone corresponding to the left and right side.
The output from the Bluetooth module is at a relatively high impedance while the speakers have a relatively low impedance. Therefore you were to connect the Bluetooth module directly to the earphones, without an audio amplifier, it would spoil the Bluetooth module’s internal circuitry.
The earphones will try and draw way too much current from the Bluetooth module and there won’t be enough voltage to power the speaker. That is why we need an audio amplifier. To provide the right intensity of current to the speaker.
The audio amplifier also has Vcc and GND pins to connect to a power source. It draws current from this to power the Speakers. Good website for explanation: https://www.headphonezone.in/blogs/audiophile-gui…