BH1404 automatic switch TV support repeater
The main circuit of the whole machine is a common single-piece FM stereo broadcast transmit integrated circuit BA1404. Its circuit has been mature. In order to facilitate the initiator homemade, the coil data is also introduced: L1, L2 is a 3.3mm 包 包 包, Bypass 5 turns, the coil is 3mm, and the length is 8mm. The coil is wound according to this data, and the emission frequency is about 100 MHz. Within the reception range of the ordinary FM radio. Other components are shown in the figure.
The automatic switch circuit portion is above the top left of the figure, and the principle is that the television is open, and a strong electromagnetic field is generated around the television, which is mainly generated by the electronically produced, television. The row scan frequency is 15.625kHz in my country, so compared with the electricity market, it is still high, as long as this electromagnetic field can be detected, the power switch of the broadcast system is opened, even if the task is completed.
In order to make the circuit as simple as possible without increasing too much cost, the electronic switch is held by the field effect tube VT. Because the driving power required by the field effect tube is extremely small, it is basically not driven. The energy of the electromagnetic rod coil L is absorbed and the energy of the electromagnetic field around the television is generated, and the D1, D2 multiplier rectification is accumulated on the capacitor C, and when the voltage is gradually increased to the opening voltage of the field effect tube VT (about 2V The above), the field effect tube is turned on? V Power is powered by the current limiting resistor R, and VT is powered by the broadcast system. The system uses a 1.5V voltage, so use the red light-emitting diode LED as a regulator tube, and it can also also mean a work indicator.
The selection of components: Capacitor C requires small leakage; 12V regulator tube is used to prevent strong pulse, protect field effect tube; 10m resistance is to automatically automatically automatically after 10 seconds after the TV Cut off the power. If this resistance is not used, it will automatically cut off after a considerable amount of time, which will be more powerful.
The unique device to be homemade is a magnetic rod coil L. The magnetic rod can be used in a medium wave magnetic bar having a diameter of 1 cm on a common radio, and do not choose a short wave magnetic bar, and the short-wave magnetic bar is shallow. The most critical is the number of coils, the number of TVs in different sizes, the number of coils can be different, in order to ensure a successful success, or more about a few turns, can be used with a diameter of 0.1mm on a magnetic bar with a mess Around the 1000-1500 circle, then weld the wire with a soft line, and then wrap the machine with the tape paper, you can connect the entire unit.
When the magnetic rod coil is placed in the appropriate position around the TV, when the light emitting diode LED is illuminated, the circuit will work normally. This position can be determined by the test, the strongest position of the electromagnetic field is approximately above the television, and the number of coils is sufficient Many, it is possible to place anywhere around the TV. After the circuit is working properly, pay attention to the antenna of about one meter, and then search with the FM radio near 100MHz, the tuning indicator lights, indicates that the signal is sent, and the audio output of the TV is connected to any sound of the circuit. The road input can hear the broadcast of the TV in the FM radio.
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