Features:  
 1: Use advanced digital audio signal processing technology (DSP) and FM phase-locked loop modulation technology (PLL) to make the sound quality more realistic, performance more stable, and long-term working frequency without deviation.
 2: LCD display is more intuitive and accurate, with extremely low power consumption and minimal noise interference.
 3: 30-level digital volume adjustment, easy to complete by key operation.
 4: Power-off automatically memorize the data before power-off.
 5: Speaker/headphone output automatic switching
 6: Using quartz crystal to stabilize the frequency, the receiving frequency will no longer drift when the temperature changes.
 7: The professional audio DSP is used to analyze and process the audio signal. When there is no signal or the signal is weak, it will automatically mute when the FM noise is large, and get rid of the annoying rustle of traditional FM radio when there is no signal or the signal is weak.
 8: Adopt incremental digital rotary encoder to adjust the volume and frequency. It has a good feel, accurate positioning, stable and durable, and 360° rotation without dead angles.
 9: 30-level digital volume adjustment range
 10: Support serial communication control, all functions of device control module with serial port such as computer or MCU can be used.
   
Due to the limited pages, if you want to know more detailed information about this product, please download it in the pottery tray----
Technical manuals, specifications, operating instructions, etc...
http://pan.baidu.com/s/1nvaCzFV
   
Product parameters: Output power: 500mW (driving headphones), 3Wx2 (driving speakers)
Frequency response range: 50Hz-18KHz
Receiving frequency range:
  Turn off campus radio 87.0MHz-108.0MHz,
  Turn on campus radio 76.0MHz-108.0MHz
Equivalent noise: ≥30dB
Supply voltage: 3.0V-5.0V
Power supply current: 1000mA at maximum volume, 60mA at minimum volume (for reference only)
Channel: stereo
 
 
Other accessories purchase guide:
 
Need to buy antenna point here:
http://item.taobao.com/item.htm?id=44840335579
 
 
 You need to use a computer to control the module through the serial port, and you need a USB to TTL level conversion module. Click here
https://item.taobao.com/item.htm?id=521966657839
 
 
 
<1>: Power
The corresponding ports of the module (marked on the PCB board)-and + are respectively connected to the negative and positive terminals of the power supply (battery). It is recommended to use a battery or other regulated power supply for the power supply. Do not use switching power supplies without filters (such as mobile phone chargers, mobile power supplies, and other switching power supplies), otherwise the interference generated by the power supply will affect the normal operation of this module. The normal working voltage of this module is 3.0-5.0V, and the power supply voltage should not exceed this range. The maximum power supply current of this module at the maximum volume is about 1A, and the battery needs to be able to output enough current.
      Note: The radio (any radio) is a radio-sensitive device, and interference from the power supply or nearby may affect the normal operation of the module. Therefore, it is recommended to use a battery or a power frequency transformer to obtain a stable voltage obtained by stabilizing the power supply for the module. Do not use switching power supplies (such as mobile phone chargers, and any other switching power supplies), power banks, switching DC-DC converters, and no working Class D amplifiers, microwave ovens and other equipment that can generate high-frequency electromagnetic interference nearby. Otherwise, the electromagnetic interference generated by these devices will be spatially coupled to the radio frequency front end of the module, causing noise in the received signal.
       
<2>: Antenna
The FM_ANT port is used to connect an FM antenna. In order to better receive FM signals, it is recommended to connect a 75cm-long whip antenna.
 
<3>: headphone/speaker output
This module comes with a 3WX2 channel audio power amplifier. If you need a speaker to connect to the speaker port, it is recommended to use a 4Ω/3W speaker. If the earphone is inserted, the audio is automatically switched to the earphone channel, and the speaker channel is automatically closed.
 
<4>Volume adjustment
     Turn the VOL encoder to adjust the volume, and the LCD screen displays the volume level.
 
<5> Frequency adjustment
     Turn the FRE encoder to adjust the receiving frequency, at the same time the LCD screen displays the current frequency, short press the encoder handle down to switch between mute and non-mute.
 
<6>Mute
Short press the VOL knob down to switch mute/non-mute
 
<7>Automatic squelch switch
  Long press the FRE knob downwards to switch on or off the automatic squelch function, the LCD display subtitles ON means to open the automatic squelch, OFF means to close the automatic squelch.
 
<8>Automatic squelch threshold (threshold) adjustment (effective when the automatic squelch switch is turned on)
  Short press the FRE knob down to enter the automatic squelch threshold adjustment interface. The user can adjust the automatic squelch threshold according to the specific usage. The adjustment range is 0-20. The larger the value, the higher the threshold, and the weaker the signal Mute. The opposite is true.
 
<9>: Serial port (no need to connect without serial port control) 
     The module reserves a TTL level serial port control interface. The communication between the TTL serial port and this module needs to be connected to the module's UART_RX, UART_TX and GND (the corresponding position on the PCB is marked), and the external MCU (microcontroller) or computer serial port can be used to send commands to control the module. Features. Note: Because the computer serial port level is not TTL level, you need to connect the RS323 level to TTL level replacement device when connecting to the computer or use a USB to TTL level serial port module to communicate with this module. Because the serial port command control module requires a certain degree of computer expertise, buyers who do not understand do not need to toss. For all information, please refer to the description of the baby, and the customer service does not provide technical guidance in this regard. 
<10>: User settings
This module can set the backlight state and whether to listen to the campus broadcast frequency band according to the user's specific usage. The setting method is as follows. When the power is off, press and hold the VOL knob to power on. The LCD displays C1 to turn on the campus broadcast. C0 indicates to turn off the campus broadcast band. The settings will take effect after restarting. To set the backlight state, press and hold the FRE knob to turn on when the power is off. B1 indicates that the backlight is always on, and B0 indicates that the backlight is turned off for 20 seconds. The settings will take effect after restarting. Change the setting status and repeat this step to switch. The factory is uniformly set to not turn on the campus broadcast frequency band, and the backlight goes out for 20 seconds without operation.
 
 
<11>: Stereo (stereo)/mono (mono) switch terminal
     The Stereo/mono terminal is used to set the FM receiving mode of the module, this terminal is floating in the stereo receiving mode, and this terminal to the ground is the mono receiving mode.
 
    Description:
    The purpose of setting the Stereo/mono switch: Due to the different principles of stereo decoding and mono decoding, the frequency band of the decoded stereo signal is wider, and the signal quality requirements are relatively high. Therefore, when listening to a relatively weak stereo broadcast, the signal-to-noise ratio will be very low, which will produce more noise. At this time, the circuit can be changed to a mono receiving state to improve the signal-to-noise ratio of the output signal. Although there is no stereo effect in mono mode, the noise is relatively small, which makes the listening effect better. In other words, this switch is used to improve the signal-to-noise ratio of the radio in the case of weak signals. Switching to mono can make the radio sound clearer in the case of weak signals. Therefore, mid-to-high-end FM stereo radios are reserved Stereo/mono switch to achieve stronger environmental adaptability.
 
  Note: The factory default setting is to turn off campus broadcast, the backlight will automatically turn off without any operation for 20 seconds, and turn off the auto mute. The user sets it according to the specific situation.
 
Two: matters needing attention:
1: The power supply voltage must not exceed the supply voltage range of this module.
2: Do not touch the back components of the module when working, so as not to affect the normal operation of the module or cause a short circuit to burn the module.
 
Four: Instructions before purchase:
1: All goods in this shop provide 7 days unconditional exchange service, if you are not satisfied with the goods you receive, you can apply for a return or exchange. The return and exchange requires the buyer to bear the return postage, and the store does not accept express shipments paid on delivery!
2: This module is a circuit board with components installed, and it needs to be wired to work. Buyers are required to have a certain knowledge of electronic operations. For buyers who do not understand electronic technology at all, it is not recommended to buy this module!
3: The products in this shop only provide limited technical support, please read the product description before use.
4: Due to various violent collisions during the express transportation process, although we have tested each product before sending it to you, and the packaging has been subjected to seismic treatment, please check whether the package is in front of the courier when receiving the goods. Intact, whether the goods are intact or missing or damaged. Sign for after confirmation!
 
 
Some basic knowledge about noise suppression:
Most FM receivers use a frequency discriminator for demodulation, and the power spectrum of the frequency discriminator output noise presents a parabolic distribution, which increases squarely as the output frequency increases. Therefore, when there is no input useful signal, the frequency discriminator demodulates and outputs noise with a larger amplitude. After these noises are amplified by the audio amplifier, they output a lot of "rusty" noise. In order to remove these noises, a squelch circuit must be added to the FM receiver that transmits voice. When there is no input signal or the input signal is very weak, the squelch system shuts off the audio output and keeps the earphone quiet. A reliable squelch system is of great significance to FM receivers.
 
 
 
 
 
 
 
 
 
 
       1. Common noise suppression methods and performance comparison
 
       The squelch circuit system is roughly divided into three categories: pilot frequency squelch, noise squelch, and carrier detection squelch. Before the voice signal is modulated, the transmitter usually adds a single tone at the low end of the voice signal frequency (below 300Hz), and then sends it for modulation and transmission. The receiving end detects this single tone after demodulation and performs squelch control. Limited by the attenuation of the squelch output and the low frequency response of the transmitter circuit, the National Military Standard stipulates that the pilot frequency of the **FM radio station is 150 Hz (plus or minus 2 Hz).
 
       The noise suppression method uses the noise pressure characteristic of the phase detector. When the radio frequency signal is strong, the output noise is reduced; when the radio frequency signal disappears, a larger amplitude of white noise is output. The noise suppression method utilizes this feature to perform noise suppression control. General narrowband FM receivers are equipped with audio amplifiers (noise extraction filtering) and simple Schmitt comparators for noise suppression. Almost all civilian FM receivers use this noise suppression method.
 
       Carrier detection squelch is to use the current of the limiter circuit before the discriminator to be proportional to the logarithm of the input signal strength in a considerable range. By detecting this current, the strength of the input signal can be obtained to perform squelch control. Many FM receiving ICs provide this input signal strength signal (RSSI). This signal is often used as output signal strength meter drive, AGC, carrier detection squelch, etc.
 
       Among the three squelch methods, the pilot squelch circuit is the most complicated, and it adds extra transmission power, which has the advantages of strong anti-interference ability and simple operation. The noise squelch and carrier squelch circuits are simple and do not need to send additional pilots. Interoperability can be achieved; some radio stations often have both pilot squelch function and noise squelch function to increase compatibility.
   With the development of digital communication technology, more and more digital algorithms are applied to squelch detection. This module uses DSP devices to sample FM audio signals. After calculations in DSP, squelch flags are sent to control audio processing. On-off of the unit.
 
 
How to adjust the noise of this module:
This module uses DSP digital squelch, which can flexibly use software to control the squelch threshold (threshold). The squelch threshold is 0-20 levels. The lower the value, the lower the squelch threshold, and the easier it is to listen to the radio signal with background noise. The higher the value, the higher the noise threshold. When the output noise is higher than the set value, it will automatically silence. The noise is turned on to mute the output. Therefore, when adjusting the squelch threshold, according to the use situation, if you want to hear the weak signal, adjust the squelch threshold down, and if you want to hear the strong signal, adjust the number up. Note that the squelch function cannot remove the background noise in the signal. It only controls the output mute by judging that the noise level of the signal exceeds the set threshold.