Infrared wireless headset circuit board design

The infrared wireless headset is composed of an infrared transmitter and a headset, and is characterized in that the headset is connected with an infrared receiver, the infrared transmitter transmits the sound signal to the external space signal, the infrared receiver collects and receives the sound signal from the external space, and sends The sound signal is transmitted to the earphone, and the sound is restored by the earphone. When watching TV programs or playing discs at ordinary times, in order to avoid disturbing other people's rest, usually use earphones to listen to the sound instead. Therefore, the above-mentioned disadvantages can be avoided by using the external line wireless earphone designed by Wenhong.

1. Infrared technology and working principle

The visible light that can be seen by the human eye is arranged according to the wavelength from long to short, in order of red, orange, yellow, green, cyan, blue, and purple. The wavelength range of red light is 0.62-0.76 μm; the wavelength range of purple light is 0.38-0.46 μm. Light with a wavelength shorter than violet light is called ultraviolet light, and light with a wavelength longer than red light is called infrared light.

Infrared remote control uses near-infrared rays with a wavelength between 0.76 and 1.5 μm to transmit control signals. Commonly used infrared remote control systems are generally divided into two parts: transmitting and receiving. The main components of the emitting part are infrared light emitting diodes. It is actually a special light-emitting diode. Because its internal material is different from ordinary light-emitting diodes, when a certain voltage is applied to its two ends, it emits infrared rays instead of visible light. The infrared receiving tube of the receiving part is a photosensitive diode. In practical applications, it is necessary to add reverse bias to the infrared receiving diode, so that it can work normally, that is, the infrared receiving diode is used in reverse when it is used in the circuit, so as to obtain higher sensitivity [1].

2. Infrared wireless headset circuit design

The infrared wireless earphone system converts the audio signal obtained from the audio equipment into an infrared signal modulated by the audio signal, and realizes wireless transmission through the infrared signal. Then demodulate the obtained infrared signal into an audio signal, and convert the audio signal into a sound signal that can be heard clearly by the human ear through the earphone of the electro-acoustic device. The infrared wireless headset system consists of two parts: a transmitter and a receiver. Figure 1 is a block diagram of the principle design. Fig. 2 is a circuit diagram of the transmitter, which converts the audio signal into an infrared signal modulated by the audio signal. Figure 3 is a circuit diagram of the receiver, which converts the received infrared signal amplitude-modulated by the audio signal into an audio signal.

2.1 Infrared transmitter circuit

The transmitting circuit is shown in Figure 2, which includes some circuits such as pulse modulation, current amplification and infrared emission. The voltage-controlled oscillator (VCO) composed of a phase-locked loop CD4060 is the core of the transmitter; when the audio signal is added to point A in Figure 2, the output of the VCO will generate a set of oscillation frequencies that are synchronized with the amplitude of the audio signal The changed frequency modulation signal is converted into an infrared frequency modulation signal by the infrared light-emitting tube and sent out [2]. The triodes VT1 and VT2 in Figure 2 are used to drive the infrared light-emitting tubes. If they do not have the same model, they can be replaced by common C1815 or 9014, but the β value of the tubes should be a little larger. The receiver consists of four parts: photoelectric conversion, pulse amplification, frequency demodulation and audio amplification. The receiver circuit is shown in Figure 3. The modulated infrared signal is first received by the infrared photosensitive tube and converted into a frequency-modulated electrical signal, pre-amplified by the FET 2SK117, frequency-selected and amplified by the μPC1373H, and then demodulated by the phase detection circuit composed of CD4046 and restored to an audio signal.

2.2 Infrared receiver circuit

The center frequencies of the two CD4046s in the receiving and transmitting circuits are both 45 kHz, so the parameters of R7 and R17, R8 and R18, C4 and C24 must be strictly corresponding and equal. The triodes VT1 and VT2 driving the infrared light-emitting tube are both working in the amplified state, and their Vbe is about 0.6 V; VT1 and VT2 can also be replaced by 9013, but the β of the tube should be greater than 100. The power supply of the transmitting circuit is not marked in the figure, and it can be obtained after LM7806 voltage stabilization during production [3]. The forward voltage drop of each infrared light-emitting tube is 1.15 V, and the emission power is less than 100 mW. The purpose of connecting three infrared tubes in series is to increase the emission power of infrared rays. In addition, because the radiation angle of the infrared light-emitting tube is limited, it is necessary to arrange the three tubes staggered by 45° when designing the circuit board. The infrared photosensitive tube can only work normally if it is applied with a suitable reverse voltage. Therefore, it is necessary to check whether the infrared photosensitive tube is reversed in the circuit when installing the circuit [4]. The receiving circuit is powered by batteries, and the power amplifier TDA2822M is bridged to reduce the power consumption of the whole machine. Inductor L10 can be made by winding 150 turns closely with φ0.06 enameled wire on the I-shaped middle circumference frame, and then installing a magnetic cap and a shielding cover. Infrared light-emitting tubes and infrared photosensitive tubes are easily damaged, and their specific parameters are shown in Table 1.

The transmitter of the infrared wireless headset does not require adjustments to work properly. When adjusting the receiver, we can point the color TV remote control panel at the receiver and press any key at will, and monitor whether there is a loud "beep" sound in the earphone; Use a sense screwdriver to repeatedly adjust the position of the magnetic cap in the inductor L10, until the audio signal is clear and loud and the noise is minimal, fix the magnetic cap with high-frequency wax, and the debugging is completed. If you feel that the sound in the earphone is dry and the sound quality is not good, you can properly adjust the resistance of the damping resistor R16; if the frequency band of the receiver is too narrow, you can try to open the circuit of R7 and R17 respectively.

Summarize

This article introduces an AM infrared wireless earphone system which is made by applying infrared technology, adopts amplitude modulation mode, and uses infrared rays to transmit audio signals. The system has the characteristics of various power supply methods, transmission distance close to 10 m, good sound quality, infrared signal is basically free from electromagnetic interference, and high cost performance. The circuit design is simple, and the use is convenient. When using audio equipment, in order not to affect other people's study and rest, the wireless earphone can be used for listening.

The above is the development example of the infrared wireless headset introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have the development needs of infrared wireless headset solutions, you can trust us. We represent a variety of single-chip microcomputers, voice chips, dual-mode Bluetooth ICs, and wifi chips. Brands include Songhan MCU, Yingguang MCU, Jerry Bluetooth, Ankai Bluetooth, Allwinner, and Realtek. Our technical services include: PCB design, microcontroller development, Bluetooth solutions, software and hardware custom development, APP development, small program development, WeChat official account development, etc. It can also undertake the design of intelligent electronic products, the development of living appliances, the research and development of beauty equipment, the application of Internet of things platform, the smart home control system, the development of TWS earphones, Bluetooth earphone speakers, the development of children's educational toys, the design of electronic education products, etc.