buying link:
small board:
https://amzn.to/2N1JduY

usb 3.5mm car bt:
(looks different but has same kit inside):
https://amzn.to/31p1cAK

How to make Bluetooth home theater
Bluetooth audio kit
Mini Bluetooth kit installation guide
how to turn a hometheater wireless
Bluetooth kit wiring

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mostly asked question:
why I didn't use 7805 ic to power the BT board while there is 12 volt line available?
ans: There is q problem called ground loop noise which arises when we power the BT IC and the amplifier ICs by same (non isolated) power supply, there will be some noise in audio.This noise is sometimes called humming noise. To overcome this issue you have to isolate either the power line or the audio transmission line between the boards. Isolation can be made by using transformer because there is no direct wire connection.audio isolation transformers aren't easily available so the easiest solution is to use a rejected phone charger for 5v.

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