Infrared earphone manufacturing method

The voice infrared transponder introduced in this article has the characteristics of simple structure, easy production, no interference and low noise.

working principle:
The transponder consists of two parts: transmitting and receiving. See Figure 1. The sound (audio) signal after frequency discrimination is amplified by the triode V to push the infrared emission tube. Because the luminous intensity of the emission tube is proportional to the current passing through, the infrared light emitted by D1 and D2 is modulated by the audio signal. In order to prevent distortion, D1, D2 must set a certain offset.

The receiving part adopts an audio amplification integrated circuit LM386. D is infrared receiving tube. When the infrared light modulated by the audio signal illuminates D, an electrical signal with the same change rule as the audio signal is generated at both ends, which is coupled to the IC via C1 for amplification. Because the IC has the power amplification capability, it can be used for listening to 1-4 headphones at the same time.

Component selection:
Transistor V selects 8050 medium power tube, Pcm = 300mW, Icm = 500mA, the power of R2 should be above 1 / 4W. D is infrared receiving tube (do not use photodiode to avoid interference and affect the receiving effect), and others are universal parts.

Installation and commissioning:
Adjust the quiescent current of the transistor V of the transmitting part to about 30mA. As long as the receiving part is installed correctly, it can work without debugging. The transmitting part can be installed inside the TV and powered by the 12V power supply inside. The signal input terminal A and B can be connected to both ends of the volume potentiometer. For TVs that use integrated circuit DC volume control, you can connect both ends of A and B to both ends of the speaker. However, you need to add a switch to turn off the speaker (you can also use the headphone output jack), adjust the volume potentiometer to make it the farthest forward without distortion. When the two launch tubes are installed, the range of the radiation area should be considered. The radiation angle of the infrared emission tube is generally about 60 degrees, so they must have a part of their radiation overlap when installing, as shown in Figure 2.
The design of this transponder has low receiving sensitivity, and its purpose is to increase the anti-interference ability. After actual measurement, the effective forwarding distance is greater than 3 meters, which can meet the needs of families.

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