Digital signal processing by means of programmable microcontroller and personal computer cooperation

Digital signal processing by means of programmable microcontroller and personal computer cooperation

Fedor M. Inochkin

School N239, 11^th form

Apt.29 Kronverkskyi pr.73/39, Saint-Petersburg, 197198, Russia

Tel: +7(812) 2326567, E-mail: finochkin-mail@mail.ru

Abstract – digital signal processing complex based on microcontroller and personal computer cooperation was designed and manufactured

1. INTRODUCTION

Nowadays communications became invaluable for the civilization. Modern communication systems are developed not for receiving and transmitting voice information (as it was in the beginning), but for digital data exchange. It expands wide abilities for developing versatile devices, supporting human in his everyday life – faxes, modems, cellular and satellite phones, signaling systems, reporting about violations directly the owner, global positioning system (GPS). Most of these devices would be too large and expensive, if they were based on discrete components and there programmable microcontrollers are irreplaceable.

2. PROJECT GOAL

The goal of a project was the development of new hardware and software for digital sound processing based on personal computer (PC) and programmable microcontroller (MC). The particular task was the construction of intellectual phone device with software for low-cost PC with DOS.

Fig1.    System general structure

1 – PC with DOS and COM port;

2 – MC (PIC16F876) board with analogue and digital periphery;

3 – Telephone line interface board with opt isolation.

PC is used for digital signal processing (DSP), recognition and synthesis of signals, coming from external device, or sending to it. Also it is used for data storage and for versatile user’s interface. Device consists of two parts – control board, where the microcontroller (MC) and basic devices, used in wide range of communication systems, such as analog-to-digital converter (ADC), digital-to-analog converter (DAC), and universal synchronous/asynchronous receiver transmitter (USART) are set. Also a part of user’s interface is integrated (for work without PC) – keyboard, LCD display, analog signal amplifiers for microphone, phones and linear signal input. This board is connected (via flat cable) with link board, which is used for immediate data transceiving into external environment (which is a “conductor” for information).

In the common case this system may include only control and link board.

Fig.2    Device structure

The task of control board is the first-step signal processing, coming from the link board, controlling this board, executing simple actions referring to the user’s wish (in this example – phone number dialing), transmitting processed data into PC or receiving them from it.

3. PROGRAMMABLE CONTROLLER

As a main controlling circuit PIC controller is used (PIC16F876). The choice is explained by its multifunctionality: just in one integrated circuit UART, ADC, serial peripheral interface (SPI) controller, parallel port are contained. Besides that, an important value for small devices has its low price and ability of reprogramming internal FLASH memory by a program running on itself. The last feature let develop the function of software update with PC and without PIC-burner. Program-uploader, running on the MC, is burned into its program FLASH memory at once – with usage of a burner. After that MC can be set on the board, and its memory can be reprogrammed with the help of PC software (data is transceived via UART interface). In this example the PC software is designed for standard INTEL HEX files. This format is supported by many compilers for this microprocessor. Mode switch (programming/normal work) can be initiated by jumper or a state word kept in the PIC FLASH memory.

Fig.3    Uploader

4. SOFTWARE

In this case, PC software is used not only for execution of simple user’s actions (phone number dialing, recording and playing sound files), but also for digital filtration of discrete analogue signal (filters are selected from standard list or specified by user), and for signal recognition. This program recognizes standard phone tone signals: dial tone, dual-tone multi-frequency (DTMF) signals. Just for this, the fast Fourier transform (FFT) algorithm was realized – straight and reversed, which enables to define quickly frequency spectrum of a signal, analyze it, change it by the user’s wish and transform back. This also enables to output on the screen either time base or frequency domain.

The software is realized for DOS, which let set it on the comparatively simple machine and can be executed in the auto answer or register mode. This makes the system cheaper. At the same time comfortable windowed interface is saved. In the view of standard facilities of programming in real-mode operating systems, such as DOS, it makes great difficulties. For solving of the problem the set of procedures-hooks was created; these procedures hook interrupts from several devices: timer, keyboard and mouse. All this, completed with functions for reprogramming these facilities in the correct mode (for example, timer counter frequency) and support of graphics interface (objects: buttons, windows …), is realized as a system of objects. The result is a chain of libraries on the C++ language. With the help of them, programming becomes as simple as an event programming, which is often used in Widows OS.

Fig.4    Event-driven programming emulation

5. MODULAR DESIGN

In conclusion, its worth to notice modular construction of system: in order to reconstruct this phone into radio phone, there is no need in projecting the entire device. It’s enough to replace comparatively simple link board and appropriate software parts. The device considered in this example can be easily transformed in signaling system, connectable to the cellular phone via UART interface (which is integrated in many low-cost phones) with ability of unapproved door opening with the help of SMS or E-mail message.

Fig.5    System hardware

6. CONCLUSION

Digital signal processing complex based on microcontroller and personal computer cooperation was designed and manufactured. Additionally:

- scales of microcontroller with analogue periphery and digital communication interfaces programming were obtained;

- technology of real-time digital signal processing and spectral analysis was investigated.

7. References

[1] U. Novikov, O. Kalashnikov, S. Gulaev, Developing devices for the IBM PC, Moscow: Ekom, 1997

[2] P. Horowitz, W. Hill, The Art of Electronics, Moscow: Mir, 1998.

[3] R. Jourdain, Programmer’s Problem Solver for the IBM PC, XT & AT, Moscow: Finance&Statistics, 1991