Currently, there are several main methods for announcing stops on city buses: (1) Manual announcement: The driver verbally announces the stop to remind passengers to get off at each stop. This method has significant drawbacks. When there are many passengers on the bus, it is difficult to hear the stop name clearly. Moreover, the driver often uses dialects to announce the stops, which is very inconvenient for outsiders. In addition, the driver may be distracted when announcing the stops, which can easily cause traffic accidents at crowded stops [1]. (2) Semi-automatic announcement: The driver needs to press the corresponding button to start the voice announcement system at each stop. This method also requires the driver to operate manually, which can easily cause traffic accidents due to distraction. Sometimes, the driver may forget to start the announcement system or press the wrong button to announce the wrong stop name, which may mislead passengers to get off the bus. (3) Using GPS positioning system for station announcement: The feature of this station announcement method is that it is a fully automatic station announcement. The GPS vehicle terminal determines the vehicle's up and down relationship and the station location based on the vehicle location information obtained every second. The station announcement is very accurate, but its production and operation costs are very high, and it requires professional personnel for maintenance, which is difficult to popularize under the current conditions [2,3]. In view of the above-mentioned shortcomings of the station announcement, this system designs an automatic bus station announcement system based on the principle of wireless data transmission and reception to improve the non-standard situation of the bus station announcement system. 1 System scheme demonstration The principle of GPS positioning system for bus station announcement: The vehicle terminal system compares the vehicle location information obtained every second with the route station location information pre-stored in the terminal to determine the vehicle's up and down relationship and the station location. It automatically broadcasts voice information to remind passengers at the vehicle's entry, exit, and turning points. At the same time, it can also display text information on the multimedia advertising screen. All operations are controlled by the vehicle terminal. The station announcement is accurate and reliable, and no manual intervention from the driver is required. If GPS's "point-to-area" positioning method is changed to a "point-to-point" positioning method, not only can the accuracy of GPS positioning be maintained, but the complexity of circuit operation can also be reduced, and the manufacturing cost can be significantly reduced. Based on the improvement ideas for the automatic station announcement system, the following two design schemes are derived: Scheme 1: A microcontroller is used to software-encode each station, and then the encoded data is transmitted within a certain spatial range via a wireless data transmission module. When a bus enters the receiving range, the onboard system receives the data, performs software decoding, and then determines the station the vehicle has arrived at based on the decoded data. The voice announcement system is then activated to announce the corresponding station name and display the station. Scheme 2: An encoding and decoding principle is used, applying a "relay" approach for automatic station announcement. Communication occurs between every two adjacent stations. When a bus departs from the first station, the information sent from the first station is transmitted to the second station, which then displays the information and sends an announcement signal. When the bus arrives at the second station, it receives the announcement information and announces the station, and so on. After comprehensive analysis, the difference between the two schemes lies in whether they use one-way or two-way data communication. Through comparative experiments, Scheme 1 is more mature, with a simpler circuit design, complete system functions, reliable performance, and lower manufacturing cost than Scheme 2. It can fully meet the requirements of wireless automatic station announcement. Therefore, this paper selects Scheme 1 to design an automatic bus station announcement system based on the principle of wireless data transceiver. 2 Hardware Circuit Design The hardware circuit of this system includes two circuit modules: the station system and the vehicle system. Both the station system and the vehicle system are designed based on the principle of wireless data transceiver. 2.1 Encoded Data Transmission System (Station System) The station system mainly consists of three parts: a microcontroller subsystem, an encoding setting circuit, and a wireless data transmission module. 2.1.1 Microcontroller System To maintain system stability, the system uses the low-power, high-performance CMOS 8-bit microcontroller AT89S51 from Atmel. This chip integrates a general-purpose 8-bit central processing unit and an ISP Flash memory unit, with 4k bytes of on-chip Flash program memory, 256 bytes of random access data memory (RAM), 32 external bidirectional I/O ports, 5 interrupt priorities with 2 levels of nested interrupts, 2 16-bit programmable timer/counters, 2 full-duplex serial communication ports, a watchdog timer (WDT) circuit, and an on-chip clock oscillator, fully meeting the requirements of this design. 2.1.2 Encoding Setting Circuit The encoding setting circuit is responsible for encoding each bus stop. This encoding is processed by the CPU and then sent to the wireless data transmission module for transmission. The circuit has an eight-bit DIP switch (in actual products, this encoding can be fixed), enabling a total of 256 combinations, which is sufficient for one bus route. When the DIP switch is toggled, the voltage level combination sent to the microcontroller's I/O port changes. The microcontroller encodes this voltage level and sends it as serial data to the wireless data transceiver module for transmission. 2.1.3 Wireless Data Transceiver Module The key component of this design is the wireless data transceiver module. In this design, the module operates at 315MHz and uses a surface acoustic wave (SAW) resonator for frequency stabilization, resulting in extremely high frequency stability. When the ambient temperature varies between -25°C and +85°C, the frequency drift is only 3ppm/°C. The circuit uses ASK modulation, and the transmission current drops to zero when the data signal stops, resulting in very low power consumption. The circuit itself does not have an encoding integrated circuit; instead, a data modulation transistor Q1 is added. This structure allows for easy interfacing with other fixed-encoding circuits, rolling code circuits, and microcontrollers without needing to consider the operating voltage and output amplitude of the encoding circuit. The module's output power is determined by the voltage. The transmission frequency remains essentially constant regardless of voltage changes. At 3V, the transmission distance in open ground is approximately 20-50m with relatively low power. At 5V, the distance is approximately 100-200m; at 9V, it's approximately 300-500m; and at 12V, the optimal operating voltage, it provides good transmission performance with a transmission current of approximately 60mA, a transmission distance of 700-800m in open ground, and a transmission power of approximately 500mW. Considering road conditions, a transmission distance of approximately 200m was selected through testing. 2.2 Data Reception and Voice Announcement System (Vehicle-Mounted System) The vehicle-mounted system mainly consists of a microcontroller system, a wireless data receiving module, a voice recording and playback circuit, a power amplifier circuit, and a display circuit. 2.2.1 In the vehicle-mounted system, the microcontroller's role is to decode the signal transmitted from the wireless data receiving module and use it as a standard to read the corresponding address. On one hand, it sends the signal to the voice chip to activate the voice chip and send out a sound signal to announce the station. On the other hand, it sends the corresponding data to the digital tube to display the station name. 2.2.2 Wireless Data Receiver Module The operating voltage of the receiver module is 5 volts and the static current is 4 mA. It is a super-regenerative receiver circuit with a receiving sensitivity of -105 dBm. The advantages of the super-regenerative circuit are: (1) The antenna input has a frequency selection circuit, which does not rely on the frequency selection of the 1/4 wavelength antenna. When the control distance is close, the external antenna can be shortened or even removed; (2) The waveform at the output is relatively clean when there is no signal. The interference signal is a short needle-like pulse, unlike other super-regenerative receiver circuits that will produce dense noise waveforms, so the anti-interference ability is strong; (3) The module itself has very low radiation. In addition, the shielding effect of the mesh grounding copper foil on the back of the circuit module can reduce the leakage of its own oscillation and the intrusion of external interference signals; (4) The frequency is adjusted to 315 MHz by using a copper core inductor with a skeleton and then sealed. Compared with the circuit that uses an adjustable capacitor to adjust the receiving frequency, the temperature and humidity stability and the anti-mechanical vibration performance are greatly improved. When the receiver module receives the signal emitted by the transmitter module, it demodulates and restores the effective data, which is then sent to the CPU after isolation processing. 2.2.3 Voice Recording and Playback Circuit Since the system adopts an automatic station announcement method, it is necessary to pre-record station names and reminder statements, necessitating the addition of a voice circuit. This system uses the ISD4004-8 voice recording and playback integrated chip. The chip employs multi-level direct analog signal storage technology, with each sample value directly stored in the on-chip flash memory. Therefore, it can reproduce voice very realistically and naturally, avoiding quantization noise and polyphony caused by the fixed-state and compression of general solid-state recording circuits. Due to the limited connections between the CPU and the ISD4004, port P2.2 is connected to the ISD4004 chip select pin /SS to control the selection of the ISD4004. Port P2.1 is connected to the ISD4004's serial input pin MOSI, from which the playback address is read. P2.3 and P2.5 are connected to the ISD4004's serial clock pin SCLK and interrupt pin /INT, respectively. The ISD4004 chip also requires connections to the audio signal output pin AUDOUT, which is connected to the power amplifier circuit via a filter capacitor. AMCAP is the automatic mute pin, which is grounded via a capacitor during use. Furthermore, since the ISD4004 operates at 3 volts, while the microcontroller requires 5 volts, a voltage regulator circuit is needed to provide 3 volts to the ISD4004. The data receiving module sends the received signal to the microcontroller, which decodes it. After verification, the signal is converted to BCD code and sent to a 74LS48 decoder for display on a digital tube. Simultaneously, the microcontroller reads the corresponding address based on the signal and sends it to the voice chip, activating the voice chip to output the sound signal and complete the voice station announcement. 2.2.4 Power Amplifier Circuit: Since the audio signal output from the voice chip has relatively low power, and a louder sound is required for station announcements, the power of the audio signal output from the voice chip needs to be amplified. Therefore, the circuit uses the TDA2822, a dual-channel audio power amplifier circuit with a wide power supply voltage range (1.8～15V), capable of operating even at 1.8V. This circuit is suitable for operation under low power supply voltages. Its characteristics include low quiescent current and very low crossover distortion, making it suitable for both mono bridge (BTL) and stereo circuitry. This system uses a BTL connection, with a maximum output power of 3W, which can drive the speaker to produce a sufficiently loud sound to meet the system requirements. 2.2.5 Display Circuit: There are many methods for driving LED digital tubes with a microcontroller. Based on the display method, they can be divided into static display and dynamic display; based on the decoding method, they can be divided into hardware decoding and software decoding. Static display means the display driver circuit has an output latch function. The microcontroller sends out the data to be displayed and then doesn't care until the next time new data needs to be sent. The display data is stable and consumes very little CPU time. Dynamic display requires the CPU to constantly refresh the display device, resulting in flickering data and consuming more CPU time. Both display methods have advantages and disadvantages: static display, while stable and consuming little CPU time, requires a separate display driver circuit for each display unit, resulting in more hardware; dynamic display, while flickering and consuming more CPU time, uses less hardware, saving circuit board space. Hardware decoding means the display segment code is handled by hardware; the CPU only needs to send out standard BCD codes, and the hardware wiring has certain standards. Software decoding uses software to perform the hardware functions; the hardware is simple, the wiring is flexible, and the display segment code is processed by the software. This design requires driving a two-digit LED display. While dynamic scanning saves circuitry, the wireless data transceiver module and voice chip require a relatively stable environment. Frequency interference generated during dynamic scanning could affect their normal operation. Therefore, the system uses a static display method and employs a hardware decoding 74LS48 driver. Although this method increases circuitry, it ensures stable and reliable system operation. 3. Software Design The system software adopts a modular structure. The flowcharts for the station system and vehicle-mounted system are shown in Figure 1. [align=center] Figure 1 Program Flowchart[/align] As can be seen from the software flowchart, the station system continuously sends its own unique code. When the vehicle is approximately 200 meters from a station, the vehicle-mounted system receives the uniquely encoded data transmitted by the station system. It decodes the data to recover the station information and automatically determines whether to stop at that station. If necessary, it issues a command to activate the voice chip, performs the corresponding addressing, and announces the station name. If no stop is needed, it automatically ignores the decoded data and does not activate the station announcement system to prevent false alarms. 4. Operational Status To test whether the system meets the design requirements, functional tests were conducted on the system, and it was compared with similar products. The results are as follows: 4.1 Performance Testing The design requirement is that the system automatically announces the bus stop when it is approximately 200 meters away from the station. Actual testing showed that the reception at 200 meters was good, the sensitivity was high, and the display matched the station number. The sensitivity decreased slightly in obstacle areas, but this did not affect normal use and met the design requirements. 4.2 Functional Comparison A comparison of the system's functions with currently popular bus stop announcement methods is shown in Table 1. Table 1 shows that the wireless automatic bus stop announcement system designed in this paper has significant advantages. Its cost is less than 100 yuan, yet it effectively performs automatic station identification, display, and voice announcement functions, avoiding the drawbacks of manual button-based announcements. Maintenance is simple, requiring no professional personnel, and it can completely replace expensive and complex announcement systems such as GPS. It is highly scalable and very suitable for promotion and use in cities of all sizes. [align=center]Table 1 Comparison of Operational Functions[/align] 5. Conclusion To address the shortcomings of manual bus stop announcements, an automatic bus stop announcement system based on wireless data transmission and reception was designed, realizing intelligent bus stop announcement functionality. Through system testing and comparison with other announcement methods, this system demonstrates low cost, high accuracy, and good potential for widespread adoption, making it a viable intelligent device for buses. The author's innovation lies in the following: Based on the principle of wireless data transmission and reception, the system uses a microcontroller to encode each stop, then transmits the encoded data within a certain spatial range via a wireless data transmission module. When the bus enters the receiving range, the onboard system receives the data, decodes it, and finally determines the stop based on the decoded data, activating the voice announcement system to announce the corresponding stop name, thus realizing the intelligent bus stop announcement function.