Wireless FM FM microphone made by 74LS04

The wireless microphone can be seen everywhere in the market, but there is no exception to consist of an LC oscillator or quartz crystal circuit. It is well known that it has an amplification (referring to small signal conditions) and inverting, so as long as three with non-door, the first tail is used, it constitutes a ring oscillator (or five, seven, nine other odd numbers. The number of levels is low, and the frequency modulation circuit is also equipped, and a wireless microphone can also be made. 74LS04 is a TTL integrated circuit with six single-ended input and non-door. The author uses three of them to make an oscillator. When the power supply voltage is 5V, the oscillation frequency is approximately 90 MHz, and the frequency is lowered when the supply voltage is lowered; the frequency is raised when the power supply voltage is increased. Of course, its oscillation will also change, but there is little impact. In this way, the author uses a way to change the power supply voltage to change the frequency (ie, to the frequency modulation). The specific practice is to use an output of an audio amplification integrated circuit BA328 as its power supply. The BA328 is an amplified circuit of a recording head. When used for tape signals, it should pick up an RC skewarn network between steps, but here is used for linear enlargement, so only one 100kΩ ~ 130kΩ is required. The resistance can be. The voltage of the BA328 output (foot) should be equal to one half of the foot (power supply) voltage. If the supply voltage is 12V, there should be 6V output, if not, this resistance should be adjusted. In addition, the 1kΩ resistance in the figure is to adjust the magnification, and reduce it increases. When speaking to the elective microphone, the voltage of the output (foot) can be rapidly changed between 5.8V to 6.2V. This voltage is sent to the foot of 74LS04 to cause a frequency modulated signal, and then the fourth The one is sent to the antenna with non-door. The power supply voltage of this wireless microphone can also be modified to 6V or 1.5V. In addition, its output power is small, and the reader can increase the high frequency amplification to improve.

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