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 +85°C 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