[Photo] Infrared remote control frequency modulation FM stereo broadcast transmitter production (BH14

The FM broadcast transmitter introduced in this article is a new type of broadcast signal transmitter, characterized by
(1) Using frequency synthesis, the frequency is stable and the adjustable range is wide.
(2) It is convenient to adjust the frequency by infrared remote control.
(3) High-performance stereo dedicated chip is adopted, with good sound quality and high separation.
(4) Adopt broadband amplifier, the frequency range of the whole machine is 30MHz --- 450MHz.
Uses: Widely used in school English listening transmission, school test signal source, can also be used to build large venues.
Main indicators: Transmitting power: 0.5W, working frequency: 30MHz--450MHz adjustable, operated by user. (Each segment is 30MHz and the step interval is 25KHz). There are two ways of stereo input and microphone input.

Main principle introduction: (1) The stereo part adopts BH1417 as the stereo coding and modulation, and the crystal oscillation uses 7.6MHz. The frequency division provides the pilot required for coding. It also provides a reference frequency for the frequency synthesis section. BH1417 itself has a frequency synthesizer (see block diagram)

Japan ROHM company has launched BH1414 ~ BH1417 FM stereo transmitter IC, its high-frequency oscillation points using frequency synthesis circuit, the oscillation frequency is very stable, and can easily change the transmission frequency. Among them, BH1414 and BH1415 are controlled by an external MCU. BH1416 and BH1417 can be changed by the parallel data setting end to transmit frequency. BH1416 is suitable for the Japanese frequency band, while BH1417 is suitable for the 88 ~ 108MHz frequency band in China.
BH1417 internally integrates a stereo modulation circuit, a phase-locked loop frequency synthesizer and a high-frequency oscillation circuit. The peripheral circuit of the FM stereo transmitter board composed of it is very simple. And it has pre-emphasis circuit, limiter circuit and low-pass filter, which can obviously improve the sound quality. The total harmonic distortion reaches 0.3%, the stereo separation is 40dB, and the RF output level is 100dB.
BH1417 adopts patch SOP22 package, the internal structure is shown in Figure 1. The functions of each pin are as follows:
The {1} and {22} pins are the left and right channel signal input terminals. The {2} and {21} pins are connected to the pre-emphasis circuit, and the time constant can be changed by the external circuit (T = 22.7kΩ × C). The {3} and {20} pins are the adjustable ends of the low-pass filter. An external 150pF capacitor can limit the input of signals above 15kHz. The {4} pin is the filter terminal, and an external capacitor can improve the ripple factor of the reference voltage. The {5} pin is the output of the stereo composite signal. The {6} pin is grounded, and the {7} pin is the output of the PL phase detector. The {8} pin is the power terminal, connected to + 5V power supply. The {9} pin is the end of the RF oscillator, which forms a voltage-controlled oscillation circuit with peripheral components. {10} Pin is the RF ground terminal. The {11} pin is the RF signal output terminal, and is connected to the antenna or the post-stage power amplifier through a band-pass filter. {12} Pin is the power supply terminal of PL. {13} and {14} feet are connected to a 7.6MHz crystal oscillator. The {15} ~ {18} pins are parallel data setting terminals, which control the output frequency of the transmitter, and the {19} pins are pilot signal adjusting terminals.
(2) The MB1504 series is a large-scale integrated digital phase-locked frequency synthesizer from Fujitsu Corporation of Japan. It adopts CMOS technology and is a monolithic serial integrated phase-locked frequency synthesizer chip with pulse swallowing function.
Structure of MB1504
The MB1504 series includes the main components such as internal oscillator, reference divider, programmable divider, phase detector, latch, shift register, dual-mode high-speed prescaler and one-bit control latch. Only an external loop filter, voltage controlled oscillator, single-chip microprocessor and other circuits are needed to form a complete full-scan frequency synthesizer. This series of chips has the following characteristics:
The maximum operating frequency is 520MHz, the amplitude of the input signal is not less than 200mVp-p; the operating voltage is 2.7 ~ 5.5V, the typical value is 3V; the power consumption is low, when the operating voltage is 3V, and the operating frequency is 500MHz, it is only 45mW.
There are two types of packages for the MB1504 series: in-line and patch. Its pin arrangement is shown in Figure 2. In the picture:
Pins 1 and 2 are the access end of the oscillator OSC, which can be connected to the oscillating crystal or used as the input terminal of the external standard frequency signal;
3-pin VP is the working voltage input terminal of the charge pump power supply;
4 pin VCC is the working power terminal of the chip, the comparator voltage;
Pin 5 DO is the output end of the charge pump source, and the phase comparator output;



6 feet GND is the chip ground;
Pin 7 LD is the lock indication terminal. When the loop is locked, LD is high, and when the lock is lost, LD is low;
The 8-pin fin is the input terminal of the prescaler, that is, the loop VCO signal output terminal;
Pin 9 is the clock input terminal, the rising edge is valid, and the clock signal;
10-pin Data is the serial programming data entry;
11 LE is load enable input terminal (built-in pull-up resistor), when LE is high, data is transferred to the corresponding latch, enable terminal;
Pin 12 FC is the output characteristic setting end of the charge pump source. When FC is low, the characteristics of the charge pump source and phase comparator can be inverted, and the reference frequency divider ratio selection can be selected;
13 pin fr is the output signal terminal of the reference frequency divider, the reference frequency;
Pin 14 fP is the output signal terminal of the programmable frequency divider. When the loop is locked, fP should be equal to fr to compare the frequency;
The 15-pin φ P and 16-pin φ r are the output of the phase discriminator, and the phase detector has two outputs.
(3) MCU XB986 is composed of single chip microcomputer:

var check_allow = "/d/Api/iscantalk.html"; var add_url = '/ d / article / write /'; function CheckLogin () {now_uid = ''; var ElecfansApi_checklogin = '/ webapi / passport / checklogin'; var logout_url = "{: U ('Login / logout')}"; var logout_url = 'http://bbs.elecfans.com/member.php?mod=logging&action=logout&refer=front'; $ .get (ElecfansApi_checklogin, function (data, textStatus) {if (data! = "") {EchoLoginInfo (data); CheckEmailInfo (data); data = $ .parseJSON (data); now_uid = data.uid; / * var login_content = 'write an article