Design of intelligent system for automatically announcing bus stop names

    At present, there are three main types of bus station announcement systems in some large and medium-sized cities in my country: manual station announcement, generally the station announcers are locals, and they announce the station in dialect, which brings great inconvenience to passengers from other places. This station announcement method is gradually replaced by other methods; semi-automatic station announcement, this station announcement method is generally controlled by the driver, which is a great improvement over the previous one, but sometimes due to the driver's negligence, there will be false reports and misreports. At the same time, since the driver's participation is required, there are certain safety hazards; automatic station announcement, this station announcement method has realized intelligence, without the driver's participation, the system automatically identifies the station, and it is relatively accurate. Now there are more studies on this method. The system designed in this paper uses infrared technology as the transmitting and receiving signal to achieve this, which is low in cost and conducive to promotion. This system is an intelligent system for automatically broadcasting bus station names. It consists of two major parts: on-board equipment and station equipment. The system uses a single-chip microcomputer (AT89C51) as the detection and driving core of the automatic station announcement, and an ISD4004 voice chip to control the station announcement. After the on-board infrared receiver receives the infrared signal sent by the station, it is processed by the single-chip microcomputer and decides which sound in the voice chip to broadcast. The voice chip plays specific voice information through the speaker according to the playback address. It can automatically play the station while the bus is driving and announce the station to passengers in time.

    System composition

    The basic components of this system are: infrared transmitting device, infrared receiving device, AT89C51 microcontroller, ISD4004 voice chip and speaker, etc.

    The hardware circuit principle block diagram of the system is shown in the figure above. Its basic working principle is: the infrared transmitting device at the station sends out an infrared signal, and the receiving device of the on-board system detects the signal through the infrared photoelectric sensor. After passing through the signal processing circuit, the optical signal is converted into an electrical signal, and the electrical signal is sent to the single-chip microcomputer for processing, and then an instruction is issued to execute the voice module to complete the automatic station announcement.

    How the system works

    1. Infrared transmitting and receiving module

    Infrared transmission and reception utilize the principle of photoelectric conversion. The infrared transmitting device converts electrical signals into optical signals. The core components for converting electrical signals into optical signals are three infrared light emitting diodes. A fixed voltage is applied to both ends of the diodes to generate continuous optical signals.

    The infrared receiving device is implemented by a phototransistor, which can convert the infrared light emitted by the infrared light emitting diode into an electrical signal. However, since the electrical signal at this time is weak and insufficient to drive the circuit and load to work normally, an analog amplifier circuit is used to amplify the signal so that it can ensure the normal operation of the subsequent circuit and load.

    Since the effective working distance of the infrared transmitting device and the infrared receiving device is limited, the loss of light source energy must be minimized. In order to maximize the light source energy of the light-emitting diode to be received by the phototransistor, lens focusing technology is adopted to achieve it, so that the working distance can reach 8 to 9 meters, or even farther, which can meet the needs of bus stop announcements.

    An infrared transmitter is installed on the platform and an infrared receiver is installed on the bus. When the bus is about to arrive at the platform, the photosensitive transistor of the infrared receiver receives the light signal from the infrared transmitter. After passing through the analog amplification circuit, the output level is low. At this time, the microcontroller will control the voice chip to realize the function of announcing the station. When the bus has not arrived at the platform, the analog circuit output level is high and the microcontroller will not perform the corresponding operation.

    2. Single chip microcomputer module

    The single-chip microcomputer module is the core module of the system, which uses the AT89C51 single-chip microcomputer. The AT89C51 is a low-power, high-performance 8-bit single-chip microcomputer that uses CO-MOS technology and Atmel's high-density non-volatile memory technology. It contains an 8-bit central processing unit and 256 RAM units, of which only the first 128 can be used as registers for users, and the rest are occupied by special registers: the chip contains 4k bytes of Flash programmable and erasable memory; there are 4 8-bit I/O ports, 1 full-duplex serial port and 5 interrupt sources. It can meet the needs of this system development.

    When the corresponding pin of the single-chip microcomputer receives a low-level signal from the infrared receiving device, the voice chip will be controlled by software to realize the station announcement. When the corresponding pin of the single-chip microcomputer does not receive the infrared signal (high level), the corresponding operation will not be performed. 3. Voice module This module uses the ISD4004 chip to realize voice station announcement. The characteristics of ISD4004 are that there is no limit on the length of the recorded sound, and the sound recording does not require /VD conversion and compression. It uses fast flash memory as the storage medium, can save data for up to 100 years without power supply, and can record repeatedly for more than 10,000 times. The recording time is long, and the peripheral circuits required for development and application are simple.

    Since the working voltage of ISD4004 is 3V, and the working voltage of the microcontroller is 5V, a voltage transformer circuit is needed; in addition, since the working power of ISD4004 is relatively small, a power amplifier circuit is needed to realize the broadcast. This article mainly introduces the broadcast of the recorded voice, and the recording process is not introduced here.

    System hardware circuit design

    This article mainly discusses the single-chip microcomputer control circuit, voice chip circuit and related transformer circuit and power amplifier circuit. The hardware circuit diagram is shown in the figure below: The infrared receiving circuit connects the Pl.0, P1.1, and P1.2 pins to connect the electrical signal of the infrared receiving device. The infrared circuit is not introduced in detail here.

    The control part is mainly composed of the single-chip microcomputer AT89C51, including the necessary peripheral circuits such as the crystal oscillator circuit, reset circuit and its connection circuit with ISD4004. The playback part is mainly composed of ISD4004, including the corresponding transformer circuit, power amplifier circuit, etc.

    From the above figure, we can see that there are few connections between AT89C51 and ISD4004. The P1.0~P1.3 pins of the microcontroller are connected to the infrared receiving circuit to control whether the station announcer plays during operation. P1.6 is connected to the chip select pin /SS of ISD4004 to control whether ISD4004 is enabled or not. P1.7 is connected to the serial input pin MOSI of ISD4004, from which the address of the playback is read, data is output from the microcontroller, and ISD4004 receives data. P3.2 and P3.3 are connected to the serial clock pin SCLK and interrupt pin /INT of ISD4004 respectively. The connection required for the ISD4004 chip also includes the audio signal output pin AUDOUT, which is connected to the power amplifier circuit through a filter capacitor. AM-CAP is the automatic mute terminal, which is grounded through a capacitor when in use. In order to make the ISD4004 work normally, the transformer circuit is shown in the figure below: 

     software design

    According to the design requirements, the program design process of using a single-chip microcomputer to realize automatic station announcement is as follows:

    The program flow chart is as follows:

    The procedure is as follows: