A design scheme for a practical infrared optical communication device

In the design process, the transmitting part uses the S8050 amplifier, which is a power amplifier to amplify its audio signal. The receiving part uses a common low-power audio amplifier D2822A. These two chips constitute the core of the infrared communication device. The device has almost no distortion in voice transmission, the transmission distance meets the requirements, and the operation is simple. When adding a relay forwarding point, changing the direction by 90 degrees, the effect is good.

1. Overall design of the scheme

1.1 System overall design block diagram

This headset consists of two parts: the transmitter module and the receiver module. The transmitter module: mainly includes the basic circuit and the infrared light-emitting diode. It mainly drives the infrared light-emitting diode to transmit the audio signal through the basic circuit under the drive of 5V voltage. The receiver module: mainly includes the S8050 power amplifier and its surrounding auxiliary components. It mainly drives the received transmission signal through the D2822A power amplifier under the drive of 5V voltage, and then drives the speaker to make sound, so that the listener can hear the music emitted by the transmitter.

The overall principle block diagram of the system is shown in Figure 1.1.

1.2 Unit Circuit Design

1.2.1 Transmitter circuit

The sound signal is led out from the audio output socket of the MP3 or signal generator. The audio signal output by the MP3 is coupled to VT1 S8050 through capacitor C1 for primary 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 DC 5V voltage flows to VT1 through resistor R4, and then provides it with working voltage, amplifies the audio signal to drive VD1 and VD2 to emit light, and transmits the signal.

The transmitting circuit is shown in Figure 1.2.

1.2.2 Receiving circuit

The receiving part of this circuit uses an audio amplifier integrated circuit D2822A for power amplification. There is an infrared receiving tube. When the infrared light modulated by the audio signal shines on the surface of the infrared receiving tube, the receiving tube converts the received infrared light signal modulated by the 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 the receiving tube. The signal is coupled to C7 for power amplification and then drives the speaker to make sound.

The receiving circuit is shown in Figure 1.3.

1.2.3 Relay Node Circuit

In the design of the relay node circuit, the transmitting circuit and the receiving circuit are connected together. The light-emitting diode and the photosensitive diode are in a vertical relationship, which can well change the communication direction by 90 degrees and extend the distance for communication.

The circuit diagram is shown in Figure 1.4.

2. System Testing

Circuit test plan analysis:

(1) When an 800 Hz single-tone signal is input to the transmitter, the RMS voltage output by the receiver is tested on an 8 ohm resistor load;

(2) When an 800 Hz single-tone signal is input to the transmitter, reduce the input signal to 0 V (i.e., block the propagation path of the infrared rays) and use a low-frequency millivoltmeter to measure the noise voltage at the output end.

3. Conclusion

This design scheme has a reasonable system architecture, good functional circuit implementation, excellent and stable communication performance, and has met the basic requirements and some of the requirements of the topic. After testing and analysis, the system can achieve: ① The transmission distance is up to two meters, and the restored audio signal has no obvious distortion; ② When a single audio signal is input, the effective value of the output voltage is greater than 0.4V, and the noise voltage is less than 0.1V; ③ The indicator light can indicate the presence or absence of the signal; ④ It can realize relay forwarding, and the communication direction changes by 90 degrees, and the signal can continue to be transmitted without obvious distortion.