FM Radio User ManualFM_RADIO_SN series----With quiet series FM radio module

Table of Contents1 Introduction………………………………..……….………………….……………....... 32: General introduction............................................................................................. 33: Selection of peripheral devices ...........................................................................44: Line connection..................................................................................................... 45: Key operation instructions................................................................................... 56: Description of external terminals......................................................................... 6,7

1 IntroductionThis article mainly introduces the operation and use of the FM_RADIO_SN FM radio module. Through familiarity with this article, users can quickly use this product.

2: General introduction

3: Selection of peripheral devices(1): Selection of power supply<1>: FM radio is a radio-sensitive device. The interference from nearby may affect the receiving station. For example, nearby microwave ovens, high-frequency welding, or high-power motors may interfere with the normal operation and reception of the radio. effect.<2>: Module power input port (DC3.0-5.0V on the PCB) -, + Connect the negative and

positive poles of the power supply (battery or regulated power supply) separately. (Be sure to check the power supply voltage and polarity before power-on. Error and then power up).<3>: The power supply voltage is required to be between 3.0V and 5.0V, and the maximum current is 2A or more, and the output ripple is small.<4>: The power supply is recommended to be obtained by voltage regulation after being rectified and filtered by a lithium battery or a power frequency transformer. Switching power supplies without filters, such as mobile phone chargers, charging treasures, cannot be used. First, the switching process of this type of power supply will generate a lot of high-frequency interference, which directly affects the receiving effect of the radio. Second, the mobile phone charger, the output voltage of the charging treasure tends to be 5V higher than the working voltage of the module, and it is easy to burn for a long time. Bad module. It is also not recommended to take the USB power from the computer, because the power supply current of the computer USB is limited, the working current of the module can reach 1A or above under the large volume state, and the long-term work will damage or protect the USB power supply part of the computer, and also from the computer. The USB power supply contains various high-frequency interference generated during the working process of the computer, which will affect the effect of the radio.

(2): Speaker selection<1>: It is recommended to use a pair of 4Ω/3W or 4Ω/5W speakers to achieve the best efficiency of the amplifier output.<2>: SP_L is connected to the left channel speaker, SP_R is connected to the right channel speaker, and SP+/SP- is connected to the positive and negative terminals of the corresponding speaker.<3>: If you want to drive the headset, plug the 3.5mm plug of the headset directly into the audio dock on the board. After the headset is plugged in, the amplifier output will automatically turn off.

(3): Selection of antenna<1>: The antenna is mainly responsible for receiving radio waves from space. According to the selection rule of the antenna, the length of the antenna is as close as possible to the 1/4 wavelength of the receiving frequency. For example, to receive a 100 MHz station, the ideal length of the antenna is L = (wave speed / Frequency) / 4 = 300000000 / 100000000 = 75cm.

<2>: It is recommended to use a 75 cm long FM radio dedicated whip antenna.

4: Line connectionConnect the antenna as shown below, the speaker and power module can start working.

5: Key operation instructions(1): Volume adjustmentV-key: short press volume - long press continuous -V+ button: short press volume +, long press continuous +(2): Frequency adjustmentCH mode:F-key: short press channel - long press to search upF+ button: short press channel +, long press down to searchFRE mode:F-key: short press frequency -0.1MHz, long press frequency continuous -1MHzF+ key: short press frequency +0.1MHz, long press frequency continuous +1MHz(3): Mute / PlayPAUSE button: Short press mute/play, long press the full band to automatically search and save the station (CH mode is valid).(4): Automatic squelch threshold (threshold) settingAt the same time, press and hold the F-/F+ button for 2 seconds to enter the automatic squelch threshold adjustment interface. The user can adjust the action threshold of the automatic squelch according to the specific usage. The adjustment range is t00-t20. The larger the value is, the higher the threshold is. The easier the signal is muted, the lower the value, the lower the threshold, and the weaker the weak signal is. Generally, the adjustment can be between t02-t05, and when t=00, the automatic static function is turned off.<5>: Backlight settingPress the PAUSE button in the power-off state and then power on and continue to press and hold. The LCD displays “HI” interface and then displays “B1” to indicate that the backlight is set to the constant light mode. “B0” is displayed to indicate that the backlight has been set to the power saving mode. There is no button operation in the power saving mode. The backlight is automatically turned off after 20s. After setting, you need to power off and power on again. Repeat this step to change the setting state (factory default is B0 or backlight power saving mode).<5>: CH/FRE mode switchingPress and hold the VOL-/VOL+ knob for 2 seconds at the same time. The LCD display CH indicates switching to the search storage mode, and the display FRE indicates switching to the manual setting frequency mode. In the CH mode, the F-/F+ button is the channel +/- function, and in the FRE mode, the F+/F- button is the frequency +/- function.

<1>: Headphone (audio output) terminalThe headphone (audio output) terminal is used to connect headphones or as an audio signal output for connection to an external audio power amplifier using a standard 3.5mm stereo audio dock. When an audio terminal is inserted, the detection pin of the audio base is short-circuited to the ground, and the microcontroller automatically switches to the audio output mode after detecting the signal, that is, the output of the on-board power amplifier is turned off, and the output amplitude of the DAC is adjusted to push the earphone or the standard for driving an external amplifier.The 3.5mm headphone interface is defined as shown below:

<2>: Amplifier output terminalThe 3Wx2 amplifier is integrated on the module board to directly drive two 3W speakers.

The SP_L corresponding port is connected to the left channel speaker, and the SP_R corresponding port is connected to the right channel speaker, wherein SP+/SP- is the positive and negative terminals of the speaker.

<3>: Stereo (mono) / mono (mono) switch terminalThe Stereo/mono terminal is used to set the module's FM receive mode. This terminal is left in stereo reception mode. This terminal is in mono receive mode.Description: The purpose of setting the Stereo/mono switch: due to the difference between stereo decoding and mono decoding, the decoded stereo signal occupies a wider frequency band, and the signal quality is the requirements are relatively high. Therefore, when listening to a relatively weak stereo broadcast, the signal-to-noise ratio will be low and will generate more noise. At this time, the circuit can be changed to the mono reception 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 clear in the case of weak signals, so the mid-to-high end FM stereo radio is reserved. Stereo/mono switch for greater environmental adaptability.

<4>: 87.0/76.0 (Campus Broadcast Band Setting) The 87.0/76.0 terminal is used to set whether the module turns on the campus broadcast band mode. This terminal is left floating to turn off the campus broadcast mode (the frequency range is 87.0-108.0MHz). This terminal is grounded. To open the campus broadcast mode (the frequency range is 76.0-108.0MHz).

<5>: SN_OUT (static signal output terminal) The purpose of setting this terminal is to reserve an external application that requires a quiet signal trigger. This terminal output works when the module's quiet function is turned on. When the internal quiet motion is output, the high level is output, and the low output is not operated. Note that the output capability of this terminal is 3.3V/20mA.

<6>: External antenna terminalThe FM_ANT terminal is the antenna signal input terminal of the FM radio, and the signal of the antenna is input therefrom. It can be connected to an external FM rod antenna via a short wire.

<7>: The UART terminal UART terminal is used to connect to the TTL serial port. It can be connected to the module through the serial port of the computer (requires USB to TTL serial cable), the TTL serial port of the MCU or other controller, and the functions of the serial control module. It can replace the operation of the button or remote control (refer to the "Serial Port Operation Manual" for specific serial port control).