This product M18/M28/M38 is a low-power Bluetooth design solution, supports the latest Bluetooth 4.2 transmission, 2-channel stereo lossless playback, and the module can be connected to Bluetooth to quickly realize Bluetooth wireless transmission, which is very convenient.
In an open environment, the Bluetooth connection distance can reach 20 meters. Widely used in a variety of Bluetooth audio reception, a variety of audio DIY modification.

Function Description:
Bluetooth V4.2 version, support Bluetooth automatic connection technology, support WAV/WMA/FLAC/APE/MP3 lossless decoding, stereo dual channel output.
After the module is powered on, the mobile phone searches for the Bluetooth name M18/M28/M38, and can play music after connecting Bluetooth.
Module blue indicator light:
When the Bluetooth is not connected, the indicator light flashes quickly;
When the Bluetooth connection is on, the indicator light is always on;
When the Bluetooth is playing, the indicator light flashes slowly.

M18(HW-425):

PIN-------Description
KEY------Button control terminal (4 button functions, additional resistors such as wiring diagram)
MUTE---Mute control terminal (output high level 3.3V when muting, output low level during playback)
VCC-----Positive power supply 5V (lithium battery 3.7V power supply requires short circuit diode)
GND-----GND
L-----------Left channel
R----------Right channel
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Package Includes:
3 * M18(HW-425) Wireless Bluetooth MP3 Audio Receiver Board
PCB size: 23*16*2.5mm
Pin pitch: 2.54mm