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Wireless microphone circuit using NAND gate

Published on Mar 14 2011 // DIY Telephone Circuits

Wireless microphone on the market everywhere, but without exception, are quartz crystal oscillators or by LC circuits. As we all know, the door has a non-amplification (refers to small-signal conditions) and the inverted phase of the effect, so long as the use of three non-door, end to end, they form a ring oscillator (or five, seven, nine and other odd ; series as much as low frequency), matched with frequency modulation circuit, the same can also be made into a wireless microphone.
  74LS04 is a TTL integrated circuits, there are six single-ended input NAND gate. I used three of them made of a NAND gate oscillator. When the supply voltage is 5V, the oscillation frequency is about 90MHz, the frequency reduces the supply voltage is lowered; power supply voltage increases the frequency also increased. Of course, the oscillation amplitude will also change accordingly, but have little effect. In this way, I used to change the ways to change the supply voltage frequency (that is, to FM). Specific approach is to use an audio amplification ICs BA328 output, as its power supply.
  BA328 is a recording head amplifier circuit, when the signal to compensate for the tape and should be in balance, feet, and indirectly a series RC network, but here is used for linear amplification, so just take a 100kO ~ 130kO resistance can be. BA328 output (foot) should be equal to the voltage pin (supply) voltage of the half, if the supply voltage of 12V, there should be 6V output, if not, adjust the resistance. Another figure in the 1kO resistor is to adjust the magnification and reduce the gain to improve it.
  Speaking against the electret microphone, the output terminal (pin) voltage can be 5.8V to 6.2V between the rapid changes in the feet of this voltage to the 74LS04 FM signal can produce it, and then by the fourth a NAND gate amplification, isolation and sent to the antenna.
  The wireless microphone can also be changed to 6V supply voltage or 1.5V. In addition, its low power output, the reader can increase the level of high frequency amplification in order to improve it.

Wireless microphone circuit using NAND gate.