Simple infrared wireless headset

When watching TV programs or playing discs at night, people usually use headphones to listen to music in order to avoid disturbing others' rest. At this time, if the headphones are connected to the TV with wires, it is not only unsightly, but also affects people's activities. If the infrared wireless headphones introduced in this article are used, the above disadvantages can be avoided.

The infrared wireless headset consists of two circuits: a transmitter and a receiver. The transmitter circuit is shown in Figure 1. The sound signal is drawn from the audio output socket of the TV. The audio signal output by the TV is coupled to VT1 through C1 for amplification and then drives the infrared light-emitting diodes VD1 and VD2 to emit light. The change of the sound signal causes the change of the light intensity of VD1 and VD2, that is, the light intensity of VD1 and VD2 is modulated by the sound.

The receiving circuit is shown in Figure 2. The receiving part of this circuit uses an audio amplifier integrated circuit LM386 for power amplification. VD3 is an infrared receiving tube.

When infrared light modulated by audio signal shines on the surface of VD3, VD3 converts the received infrared light signal modulated by sound into an electrical signal, that is, an electrical signal with the same change rule as the audio signal is generated at both ends of VD3. This signal is coupled to LM386 through C9 for power amplification and then drives the speaker to make sound. Since LM386 can output about 0.5W of power, the receiver can be used for multiple pairs (1 to 4 pairs) of headphones to listen to at the same time.

Transistor VT1 uses medium power tube 2SC8050, PCM=3mW, ICM=500mA, and the power of R2 should be above 1/4W. VD3 is an infrared receiving tube (do not use photodiode to avoid interference and affect the receiving effect). VD1 and VD2 should use transparent shell varieties. Those varieties whose internal electrodes cannot be seen from the outside will have a very short communication distance.

During installation, adjust the quiescent current of the transmitting part transistor VT1 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 TV. The signal input terminal can be connected to the two ends of the volume potentiometer. For TVs with DC volume control for the accompanying sound amplifier, a 5.1kΩ resistor can be connected in series in front of C1 and the input terminal can be connected to the two ends of the speaker. Adjust the volume potentiometer so that it can forward the farthest distance (3~4m) without distortion. When installing the two infrared transmitting tubes (VD1. VD2), their radiation area range must be considered. Since the radiation angle of the infrared transmitting tube is generally around 60°, their radiation space range must overlap partially during installation, as shown in Figure 3.
 

In addition, it should be noted that it is best to turn off the fluorescent light when using the infrared headset, otherwise there may be interference noise.