This article describes this wireless headset with the infrared to achieve a close pass of the audio signal, and transmit and receive part by the digital circuit structure, low production costs, it is relatively easy to debug, for the majority of electronics enthusiasts self-imitation.
The transmitter circuit shown in Figure 1, which contains part of the circuit of the pulse modulation, the current amplification and infrared emission. By phase-locked loop CD4O46 constitute a voltage-controlled oscillator (VCO) is the core of the transmitter; when the audio signal is applied to point A in Figure 1, the VCO output will produce an oscillation frequency with the size of the amplitude of the audio signal synchronization change the FM signal, the infrared LED transform infrared FM signal is sent.
The transistor VT1 and VT2 in Figure 1 is used to drive the infrared LED, if not the same model can also be used common C1815 or 9014 instead, but the β value of the tube preferably made large.
Receiver by the photoelectric conversion, pulse amplification, frequency demodulation and audio amplification of four parts, the receiver circuit shown in Figure 2. By the modulated infrared signal is first infrared photosensitive tube receiver and converted to the FM signal pre-amplification, after the FET 2SK117, μPC1373H frequency selection, amplification and then the CD4046 constitutes a phase discriminator demodulation and restore the audio signal.
Two in the receiving and transmitting circuit CD4046 of the center frequency of 45 kHz, so the R17 and R7, R8 and R18, C4, and C24 of the parameter must correspond exactly equal. Drive the infrared LED transistor VT1 and VT2 are working in the zoom state, the Vbe of about 0.6V; VT1 and VT2, available 9013 replacement, but the tubes of β should be greater than 100. The power of the transmitter circuit is not marked in the figure, making available the LM7806 voltage regulator.
Each infrared LED’s forward voltage drop of 1.15V, transmission power less than 100mW, the three infrared tubes in series aimed at increasing the transmit power of the infrared. In addition, due to the limited angle of the infrared LED radiation in the design of the circuit board should be three just sub-staggered 45 ° arrangement.
Infrared photodiodes only with the reverse voltage to work properly, check the infrared photodiode in the circuit, whether the reverse should be noted that in the installation of the circuit. The receiver circuit using a battery-powered, the amplifier TDA2822M carried the bridge is to reduce the machine power. Inductor L10 in the week-shaped skeleton φ0.06 enameled wire tightly wound 150 turns mounted on magnetic cap and shield in the system.
Infrared LED and infrared photodiode is easy to damage, and their specific parameters, such as shown in the table.
Infrared wireless headphone transmitter does not need to adjust to normal work. To adjust the receiver, we can first color TV remote control board at the receiver and free to press any key, whether there is a loud “beep” in the headphones; and then the receiver at the transmitter, with no sense screwdriver repeatedly adjust the position of the magnetic inductance L10 cap until the audio signal clear and loud noise the most hours of the magnetic cap with high-frequency wax fixed, debugging is complete. If it feels dry sound in the headphones, the sound quality is poor, may be appropriate to adjust the damping resistor R16 resistance; receiver band is too narrow, you can R7 and R17, respectively, open to try.