This article introduces the TDA7088T integrated block developed by Philips, using a 16-foot double-column flat package, and the operating voltage is 3V, which includes all the functions of the FM radio receives the audio output audio signal from the antenna. In addition, a search tuning circuit, a signal detection circuit, a static noise circuit, and a frequency lock ring FLL circuit in which the frequencically biased frequency in compression is also provided. The intermediate frequency of the TDA7088T circuit is designed to 70kHz, and the peripheral circuit does not have a medium frequency transformer, where the frequency selection is accomplished by the internal RC intermediate frequency filter. The image digital tuning radio uses an electric tuning button (RUN), and the other is the reset button (RESET). After the circuit is powered on, press the search button, the circuit automatically searches the station to the high-end search station by the low end of the frequency, once the radio signal is searched, and the tuning is automatically stopped. If you follow the search buttons, the circuit continues to search for the high-frequency side. When tuning to the highest end of the FM reception frequency, simply press the reset button, the local vibration frequency is returned to the lowest end, and the search tuning is restarted. The production and debugging method of the machine will be described below. The machine uses a headphone cable as an antenna, and the FM signal induced by the earphone cable enters the mixing circuit from the TDA7088T integrated block {11} foot, generates a 70 kHz intermediate frequency signal after mixing with the vibration mix. The radio signal is sent to the integrated block {11} and {12} feet, inductance L2, capacitance C10, C11, C12 constitute an input circuit, and the frequency of the circuit is determined by L1, C5, and varactor diode D1. As can be seen from the figure, C1 is a static noise capacitor, C6 is an intermediate frequency feedback capacitor, and C7 is a low-pass capacitor, the {15} pin is a search tuning input, and C14 is a filter capacitor, {16} pin is electrical tuning, AFC output. When assembled, the components are welded to the wiring board when assembled. It is necessary to pay special attention to the two hollow coils, which is less oscillating coils, and the other turns is in the 4 and 5 feet of the integrated block, and the other number is the input tuning circuit coil, which is installed in {11} and Between the {12}, due to the low frequency frequency is selected, the local oscillator signal is easy to interfere from the antenna input end to the circuit, so the position of the two coils is placed vertically. At the time of welding, pay attention to the direction of the tube of the TDA7088T, do not make the wrong, soldering iron shells to ground, do not sell components on the wiring board in the case where the circuit board is powered. After the installation is complete, you must carefully check it, avoiding the phenomenon of mistake, domain welding and short circuit, and confirmed the next step-by-step debugging. The general plant mass production is to debug the radio with a sweeper. The amateur fan does not have these instruments, and the high-frequency signal generator can be used to debug, or the local FM broadcast station can be commissioned. First, use a DC power supply to the frequency overlay of the tuning radio on the foot, adjust the DC power supply to the voltage value of VCC-0.1V (such as the power Vcc = 3V used by the radio to 3-0.1 = 2.9V), The spacing of the oscillation coil adjusts its inductance to receive the radio to receive the 87 5MHz signal, then adjust the DC power supply to the voltage value of VCC-1.6V, as long as the 108MHz signal can be received. After the frequency coverage is adjusted, remove the DC power supply, that is, the assembly is completed. The machine receives frequency ranges from 88 to 108 MHz (since the SC1088 integrated block is the same as the TDA7088T integrated block performance and pin, it can be directly supplied to each other). The circuit is shown in the figure above. Special specifications can be adjusted to 76 to 106 MHz, which is only 78 mm × 44 mm × 14 mm.
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