Design and implementation of electronic signage voice system based on Wifi

Electronic kanban is a management tool that combines kanban management with information technology based on computer technology. It was originally created by Toyota Motor Corporation in the 1950s as a tool for delivering production and delivery instructions inspired by the operating mechanism of supermarkets.
Traditional management kanbans are placed on the production line to display real-time information related to the production line, such as target output, actual output, and qualified rate. Through the kanban, managers and producers can know the various production conditions of the assembly line through the information shown on the kanban. The system in which managers conduct the entire production scheduling and coordinate the issuance of instructions to the offline line based on the situation at the production site. The more timely and targeted the instructions are, the more tacit and efficient the cooperation of each link of the production line will be. The author provides a new type of electronic kanban, which, in addition to the traditional kanban functions, adds card swiping authentication, video monitoring, and voice call functions.

1 System composition
The system composition is shown in Figure 1.

The electronic signage PC is installed with Windows operating system and database. The electronic signage hardware distributed in each work group uses a development board with ARM2440 as the CPU. The main frequency is 400 MHz, and the software is the Linux operating system. The development board has 128M RAM, 64M Flash, sound card, USB host, serial port and other interfaces.
The embedded system composition is shown in Figure 2.

The wireless network card uses rt3070 wireless network card access: USB interface. The camera is a USB interface. The embedded system has interfaces such as sound card and serial port. The serial port is connected to the IC card reader, and the IC card information is obtained and transmitted to the host computer through the wireless network. The database information is authenticated and the corresponding time is recorded.
Each group arranges the wireless network according to the distance. As shown in Figure 3, the solid line part is the factory wired network, and the dotted line part is the wireless network.

The lower computer collects field data and video and transmits them to the summary board in real time, and can transmit real-time sound data through the sound card.
2 Upper computer program design
Voice transmission uses mono, 16 bits, 8,000 Hz sampling frequency, and collects 16 k data per second. The upper computer program is written in Delphi and calls the windowsAPI-WaveInOpen function to open the device. And set:

call waveInAddBuffer to obtain sound data, and the sound data obtained uses adaptive differential pulse code modulation. The algorithm uses a simple mapping method to adjust the quantization step size. For an input PCM value X(n), it is subtracted from the predicted value of X(n-1) at the previous moment to obtain d(n), and then d(n) is encoded according to the current quantization step size, and the quantization step size is adjusted with the encoding value of this sample point. At the same time, the predicted value of the current sample point is obtained for the encoding of the next sample point. Through this algorithm, the sample point can be encoded into a 4-bit code stream, a sign bit and 3 amplitude bits. The algorithm is simple to encode and decode, and only subtraction and table lookup operations are performed. The CPU requirements are not high.
The compressed data is transmitted through the idudpclient control. The reference code is as follows:
idudpclient 1. host: = IP
idudoclient 1. port: = PORT
idudoclient 1. SendBuffer
The idudpclient control brodcastenable property can enable broadcasting. With broadcasting, all lower computers can receive data packets sent by the upper computer.
Delphi uses the IdUDPServer control to listen to the port to read the sound data of the lower computer, decode and call waveOutOpen(),
waveOutPrepareHeader(), and wave()utWrit() to play the sound. The program flow is shown in Figure 4.

3 Lower computer program design
The lower computer is a management board distributed in the production line or workshop. The Linux operating system is used. Under the Linux operating system, the hardware is regarded as a device file. The file is located in the dev directory, and the file name is dsp. The read function is used to read the sound, and the write function is used to play. The lower computer software also starts two threads. One thread listens to the corresponding port to obtain the compressed sound data and decompresses it for playback, and the other thread collects the sound card data and compresses it for transmission.
1) First open the device file:
fd=open("/dev/dsp", oflag); set the sampling bit number, frequency, etc.
2) Establish thread 1: pthread_create.
Establish udp network connection sockfd()
to read the sound card:
read(fd, inbuf, sizeof(inbuf));
3) adpcm encoding and transmission
4) Establish thread 2
to establish a udp network connection to listen to the port, obtain network data, and decompress it.
Write to the sound card device:
write(fd, outbuf, sizeof(outbuf));
The program flow is shown in Figure 5.

4 Conclusion
Through practice, the new management dashboard can reflect the situation on site in real time and accurately. It improves the transmission of production and management information and the traditional monitoring mode. The dashboard is easy to install and can be adaptively networked according to the existing wireless routing without considering wiring. In addition, voice broadcasting and real-time voice calls between upper and lower computers are convenient for management personnel and operators.