Item Type: Module Function / modelM18M28M38 MICRO power supplyNoYesYes Audio headphone InterfaceNoYesNo Built-in amplifierNoNoYes(5W+5W) Lithium battery poweredYesYesYes Support USB sound card, free driveNoNoYes Volume memory/adjustmentYesNoNo MUTE mute interfaceYesNoNo Button extensionYesNoNo for Bluetooth versionFor Bluetooch V4.2 Support for Bluetooth protocolHFPV1.7, A2DPV1.2, AVRCPV1.5, AVCTPV1.2, AVDTPV1.2 Format supportSupport WAV/WMA/FLAC/APE/MP3 un-decoded, stereo two-channel output Operating Voltage5V/3.7V-4.2V Not connected Broadcast state 5.5MA Connection work state20MA Deep sleeping3UA Transmission distance20 meters (empty or low interference environment) Operating temperature-40C to +85C Sensitivity-87dbm MH-M18: NumberPinDescription 1KEYButton control terminal (4 button functions, additional resistance required) 2MUTEMute control terminal (output high level 3.3V when muting, output low level during playback) 3VCCPositive power supply 5V (lithium battery 3.7V power supply requires short circuit diode) 4GNDNegative power supply 5LLeft channel output 6RRight channel output MH-M28: NumberPinDescription 15VPower positive 5V 2GNDNegative power supply 3VBATLithium battery positive 3.7-4.2V 4LLeft channel output 5RRight channel output 6AGNDAudio ground MH-M38: NumberPinDescription 15VPower positive 5V 2GNDNegative power supply 3VBATLithium battery positive 3.7-4.2V 4L+/L-Left channel output (direct speaker) 5R+/R-Right channel output (direct speaker) Blue Module: The light blinks when for Bluetooth is not connected The indicator light usually lights up when for Bluetooth is connected For Bluetooth appears during playback, slow flashing 1M18: MUTE mute control terminal: used to control the power amplifier board. When muting, MUTE outputs a high level of 3.3V, and outputs a low level during playback. KEY button control: This function requires additional connection of resistors and buttons to achieve Volume power off function: The default output is 100% volume. Press the button to control the volume increase and decrease. If the control volume is less than 15%, the volume output will be 15% after power?on; if the control volume is greater than 15%, the original volume will remain unchanged after power?on. 2M28: Power supply: It can be directly powered by the MICRO USB for Android cable 5V, or it can be connected to a 5V power supply or a 3.7V lithium battery. 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. 3M38 Power supply: It can be directly powered by the MICRO USB for Android cable 5V, or it can be connected to a 5V power supply or a 3.7V lithium battery. The maximum working current is 5V2A. It is recommended to use 5V2A regulated power supply for better sound quality. Support USB sound card, free drive (plug and play) Connect the module to the computer with the USB cable, and the computer can play music through the module amplifier output. 4For Bluetooth V4.2 version of for Bluetooth automatic technology, supports WAV / WMA / FLAC / APE / MP3 lossless decoding, stereo two-channel output 5After powering on the module, the phone searches for the for Bluetooth name MH?M18 / MH?M28 / MH?M38, and can play music when connected to for Bluetooth. 6Widely used in various for Bluetooth audio receivers, DIY conversion of various sounds, etc.1 xModule