Production of FM Wireless Headphones

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Production of FM Wireless Headphones [Copy link]

With the emergence of new TV sets, wireless headphones have brought new convenience to users. In fact, it is not difficult for radio enthusiasts to own a pair of wireless headphones. You can make it by making it yourself. Here, the author introduces a FM wireless headset for those who are interested to experiment with.

Figure 1 is the transmitting circuit of the wireless headset. The audio signal obtained from the headphone jack of the TV through the stereo headphone plug pp is amplified by BG1, and the limiting circuit composed of D1, D2, C2, and C3 is limited and then sent to the high-frequency oscillator composed of BG2 and other components. The modulated FM signal is coupled to the antenna through C7 and transmitted outward.

Figure 2 is the receiving circuit, with the dedicated FM receiving module IC1 TDA7021T as the core. The demodulated audio signal is output from the foot and sent to IC2
LM386 for power amplification to drive the earphone to sound. Transistor BG
9018 and other components form a high-frequency amplifier stage to improve the receiving sensitivity. Adjusting the adjustable capacitor C23 can change the receiving frequency to align it with the transmitting frequency of the transmitter.

Component Selection　

　　Since the circuit operates at high frequency, all non-polar capacitors are high-frequency ceramic capacitors. Coils L1 and L2 are made of ∮1mm silver-plated wire wound on a ∮4mm round rod with a 5T die-casting method. The transmitting antenna is erected on the transmitter with a 10cm long thick copper wire. The receiving antenna is made of a rubber wire of appropriate length wound on the headphone belt loop. There are no special requirements for other components.

Circuit debugging Circuit debugging is very simple. Adjust the collector current of transistors BG1 and BG2 in the transmitting circuit to 0.5mA and the collector current of BG in the receiving circuit to 0.3mA to make it work normally. Then adjust C23 to align the frequencies of the transmitter and receiver and put it into use. One thing to note is that if the sound heard in the headphones is distorted, it means that the input signal of the transmitter is too large and the volume of the TV should be turned down.