1.Description:

• It is a FM Stereo Audio Transmitter.
• It uses advanced digital audio signal processing technology (DSP) and FM phase-locked loop modulation technology (PLL) to make the sound quality more realistic,the performance is more stable,and the working frequency for a long time has no offset.

2.Feature:

• It has built-in 30-level digital volume adjustment,which can be easily completed by key operation.
• It supports automatic memory function after power failure,and can save the frequency used before power failure after power failure.
• It supports serial AT command control.
• It adopts the chip type high-precision quartz crystal to stabilize the frequency,and the transmission frequency will not drift when the temperature and voltage change.
• It supports Bluetooth audio to FM transmission and line input audio to FM transmission.

3.Parameter:

• Product Name:FM Stereo Audio Transmitter
• Input Voltage:DC 3.7V-5V
• Working Current:150mA
• Output Power:+22.5dbm (170mW)
• Audio Frequency Response Range:20Hz-15KHz
• Transmission Frequency:76.0MHz-108.0MHz
• Frequency Adjustment Step:0.1MHz/time (short press of button),1.0MHz/time (long press of button)
• Modulation Mode:Standard FM
• Equivalent Noise:>/=30dB (sound quality close to CD quality)
• Transmitting Antenna:75cm rod antenna
• Transmission Distance:The FM transmitter module is connected to a 75cm standard FM radio rod antenna,and the radio uses Desheng PL-660,and the measured signal in the open field covers a radius of 500 meters.(Note:The transmission distance is for reference only,and the coverage distance is slightly different due to the difference in the use environment and receiver sensitivity)

4.Pin Definition:

• L:Left channel audio signal input
• AGND:Analog audio signal ground
• R:Right channel audio signal input
• V+:Short press volume+/long press continuously+
• V-:Short press volume-/long press continuously-
• F+:Short press frequency+0.1MHz/long press continuously+1MHZ
• F-:Short press frequency -0.1MHz/long press continuously -1MHZ
• P:Short press to mute
• DM:USB DM data cable
• DP:USB DP data cable
• TX:TTL serial port sender
• RX:TTL serial port receiver
• +5V:5V power input terminal (3.7-5V power supply range)
• G:Power ground
• ANT:External FM transmitter antenna

5.External Button Function Description:

1.Volume + key:

• Short press:volume +1
• Long press:volume increases continuously

2.Volume - Key:

• Short press:volume -1
• Long press:volume decreases continuously

3.Frequency + key:

• Short press:frequency +0.1MHz
• Long press:continuous +1MHz

4.Frequency - Key:

• Short press:Frequency - 0.1MHz
• Long press:Continuous -1MHz

5.Mute/mode switch key:

• Short press:toggle mute/unmute
• Long press:switch to select line input audio transmission mode or Bluetooth audio transmission mode

6.Power Supply Description:

• The module adopts DC 5V power supply,and the power supply is recommended to use a linear regulated power supply that is rectified,filtered and stabilized by a transformer.
• Switching power supplies without filters (such as mobile phone chargers,power banks,switching DC-DC power supplies) cannot be used,otherwise the high-frequency interference generated by the power supply will affect the normal operation of the module.
• The working voltage of this module is DC 3.7-5.0V (the RF output power will be relatively small when the voltage is low),the power supply voltage should not exceed 5V,and the positive and negative poles of the power supply should not be reversed,otherwise the module will burn out.

7.Antenna Selection Instructions:

• The ANT port is used to connect the FM antenna.The length of the antenna is related to the wavelength of the RF signal.
• In order to better transmit FM signals,a 1/4 wavelength antenna is usually used.The 1/4 wavelength of the FM frequency band is about 75cm,so it is recommended to connect a rod antenna with a length of 75cm.
• The antenna should be placed as high as possible and there are no obstacles nearby,so that the transmitter can work in the best state and achieve the longest transmission distance.

8.Line Audio Input Description:

• L,AGND,R are the left channel of the line audio input,the audio signal ground,and the right channel.

• By connecting with the corresponding lines of the line audio input signal lines of audio output devices such as mobile phones,computers,CD players,etc.,the module switches to the line audio input mode state,and the signals from these audio sources can be forwarded to the FM band for broadcast.

• As long as the nearby FM radio is adjusted to the same transmission frequency as the module,the sound from the line input port can be heard.

9.Bluetooth Audio Input Instructions:

• This module supports the Bluetooth audio forwarding function.After the module is switched to the Bluetooth audio forwarding mode,the LCD Bluetooth icon will light up.If the Bluetooth is not connected,the Bluetooth icon will flash at a frequency of 500ms.If the mobile phone Bluetooth audio is connected,the Bluetooth icon will be on for a long time.

• After the module is connected to the mobile phone through Bluetooth,the audio signal of the mobile phone music player playing music will be wirelessly transmitted to the FM module through Bluetooth,and the module will then transmit the audio signal through FM radio.

• As long as the nearby FM radio is adjusted to the same transmission frequency as this module,you can listen to the sound from the mobile phone music player.