Universal Chinese Character Text Broadcasting System Designed Based on Single Chip Microcomputer

Embedded voice playback systems are increasingly widely used. There are several methods for playing Chinese voice, including recording chip method, voice synthesis chip method and Chinese voice library method. The capacity of Flash memory is increasing, and using Windows Speech SDK, Chinese voice files can be easily extracted, so the Chinese voice library method is widely used.

The Chinese character voice library method can be divided into two categories: dedicated voice playback and general voice playback. The dedicated voice playback system only stores a small amount of fixed voice resources and requires a smaller storage capacity, but its application range is limited. The general voice playback system stores the single-word voice resources of all Chinese characters with different pronunciations, and can realize the voice playback of any text combination. It is suitable for occasions where the playback content is frequently updated. This system consists of a voice library of 1220 Chinese character pronunciation files with different pronunciations, which are stored in a Flash memory, and realize an embedded general Chinese character text voice playback system based on SPCE061A. The system has simple hardware, is easy to use, and has low cost, and is suitable for application systems such as bus stop announcers.

1 Hardware Principle

The voice library composed directly of the wave pronunciation files of Chinese characters takes up a lot of storage space. After the voice files are compressed, the space occupied by the voice library data in the Flash memory can be greatly reduced. Lingyang provides a variety of compression algorithms for voice playback. This system uses the SACM_S480 compression algorithm of code excited linear prediction (CELP) coding, and its compression ratio is 80:3. The compressed voice resource data can be stored in a 512 kB Flash memory.

The voice playback system with ordinary single-chip microcomputer as the core requires more peripheral devices and circuits in hardware, such as memory, D/A converter, etc. The slow voice decompression speed in software will affect other operations. If the voice playback system is implemented with an embedded microprocessor, the cost is too high. Lingyang's 16-bit single-chip microcomputer SPCE061A is the best choice. It has DSP instructions and integrates the A/D, D/A and other functional modules required by the embedded voice system into one chip, with strong programmable audio processing functions. Lingyang also provides SACM_LIB voice library (this system uses SACMV26e.lib) to realize recording, playback and voice recognition functions.

The hardware principle of this system is shown in Figure 1. It mainly consists of two chips: SPCE061A microcontroller and external Flash memory SPR4096A. SPCE061A runs all software functions for voice decoding and playback and other operations. Its D/A output is connected to the speaker through the audio amplifier SPY0030. SPR4096A stores all voice information including the Chinese character pronunciation number index table, voice resource address index table and voice resource data.

There are three working modes for general text voice playback: pre-stored fixed text playback, playback after receiving text, and real-time text playback. Real-time text playback has the highest requirements on the system's software processing capabilities and can best test the coordination between the system's voice playback operation and other operations. Therefore, this system uses real-time text playback to debug the program, that is, the serial port inputs Chinese characters while playing text. In terms of hardware, the UART of SPCE061A is connected to the RS-232 of the PC.

SPCE061A has a built-in ICE (in-circuit emulator) debugging interface, which can realize online simulation, debugging and downloading. Program debugging is very convenient, which is one of the main reasons for choosing SPCE061A. In terms of hardware, the ICE debugging interface is connected to the parallel port of the PC. In addition to programmable audio processing functions, SPCE061A also has rich I/O ports, clock sources and interrupt sources, Flash storage up to 32 k words, RAM has 2 k words, and can perform complex control operations while playing voice.

The capacity of SPR4096A is 512 k×8 bits, divided into 256 sectors, each sector is 2 kB, and can be configured as BMI (bus memory interface) or SIF (serial interface bus). In order to save I/O ports, this system uses a serial interface. This serial interface is a SIO interface defined by Lingyang, which also uses two signal lines SCK and SDA, but the data format is slightly different from I2C or SPI. IOB0 of SPCE061A is the clock signal SCK, and IOB1 is the data signal SDA.