PIN NO Function Description 1 KEY Button control terminal (4 button functions, additional resistors such as wiring diagram) 2 MUTE Mute control terminal (output high level 3.3V when muting, output low level during playback) 3 VCC Positive power supply 5V (lithium battery 3.7V power supply requires short circuit diode) 4 GND GND 5 L Left channel 6 R Right channel   PIN Description 1 5V 5V 2 GND GND 3 VBAT lithium battery 3.7V power supply3.7V-4.2V 4 L Left channel 5 R Right channel 6 AGND Audio GND   PIN Description 1 5V 5V 2 GND GND 3 VBAT lithium battery 3.7V power supply3.7V-4.2V 4 L Left channel 5 R Right channel MH-M18/M28/M38 is a low-power Bluetooth design solution that supports the latest Bluetooth 4.2 transmission, two-channel stereo lossless playback, and Bluetooth wireless transmission when the module is connected to Bluetooth, which is very convenient. In an open environment, the Bluetooth connection distance can be up to 20 meters. Widely used in a variety of Bluetooth audio reception, a variety of audio DIY modification. For your different needs, we offer 3 versions for you to choose from: 2..Function /Pin definition  1. Bluetooth V4.2 version, support Bluetooth automatic connection technology, support WAV/WMA/FLAC/APE/MP3 lossless decoding, stereo dual channel output. 2. After the module is powered on, the mobile phone searches for the Bluetooth name MH-M18/MH-M28/MH-M38, and can play music after connecting Bluetooth. 3, 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; The following is an introduction to each version: MH-M18: PCB size: 23*16*2.5mm (length, width and height) Pin pitch: 2.54mm (can be directly attached or soldered) 3. Function /Pin definition  1.The interface adopts a semi-hole process, which is convenient for customers to directly attach or solder to the board. 2.1. Bluetooth V4.2 version, support Bluetooth automatic connection technology, support WAV/WMA/FLAC/APE/MP3 lossless decoding, stereo dual channel output. 1. Power supply: You can directly use the MICRO USB Android cable 5V for direct power supply, or you can also connect 5V power supply or 3.7V lithium battery (as shown below). Note that the 5V and 3.7V power supply interfaces are different. The 5V voltage is connected to 5V and GND, and the 3.7V lithium battery is connected to VBAT and GND. 2. Audio output: The earphone can be directly connected to the 3.5mm audio interface, or it can be wired for the audio input of the power amplifier board (the interface L/R/AGND can be directly wired as shown). MH-M38 1. Power supply: You can directly use the MICRO USB Android cable 5V for direct power supply, or you can also connect 5V power supply or 3.7V lithium battery (as shown below). Note that the 5V and 3.7V power supply interfaces are different. The 5V voltage is connected to 5V and GND, and the 3.7V lithium battery is connected to VBAT and GND. The maximum operating current is 5V2A. It is recommended to use a regulated 5V2A power supply for better sound quality. 2. Support USB sound card, free drive (plug and play). Connect the module to the computer with a USB cable, and the computer can play music through the module amplifier output.