Introduction

TDA7313 audio processor have been used for more than ten years in the industry because of its simplicity, functionality and good parameters like low distortion, low noise. Chip is based on BIPOLAR/CMOS technology and can be used in various applications including car radios, Hi-FI, simple mixers.

TDA7313 chip has 3 external stereo inputs, that allows to multiplex three incoming sound sources, volume control with steps of 1.25dB, Treble and BASS control, Loudness function, Each of four outputs have distinct control that allows to balance outputs. Chip can be controlled via I2C (TWI) interface.

Description

The idea of this project was to construct independent audio processor which can be embedded in any audio system with ability to control settings with simple button interface with menu preview in LCD.

The intent was to cover all audio-processor functionality within LCD menu.

Circuit and PCB

Circuit diagram is pretty the same as in datasheet plus Atmega8 control circuit.

Circuit diagram

Control board was projected in single sided PCB board so it was easier and simpler to reproduce it.

Here is a prototype board with buttons and LCD connected.

Some mistakes found on board are already corrected and included in newest project files.

Hardware part is the easiest one.

Firmware design

Firmware writing is always most interesting and time consuming task. The idea was to implement a menu system that allows to control all parameters of audio processor:

• Volume [-78.75dB to 0dB] + Mute;

• BASS [-14dB to 14dB];

• Treble [-14dB to 14dB];

• Channel select [Ch1, Ch2, Ch3];

• Input Gain for selected channel [0dB to +11.25dB] +Loudness;

• LF speaker attenuation [-38.75dB to 0dB];

• RF speaker attenuation [-38.75dB to 0dB];

• LR speaker attenuation [-38.75dB to 0dB];

• RR speaker attenuation [-38.75dB to 0dB];

For this linear menu system was implemented where parameter is expressed as progress bar except channel select:

Control is done with specially oriented buttons:

[Up] and [Down] buttons are used to navigate in the menu, [+] and [–] buttons is for change parameter value. Hold [+] or [–] button for a longer time and parameter is increased continuously. [Mute] button is used to mute signal when active menu is Volume and set Loudness when active menu is Input gain. Mute and Loudness settings are indicated in Volume menu as MT and LD strings.

There you can download menu simulation Proteus files (menusimulation.zip). Archive includes Proteus_LCD.DSN file (tested with Proteus 7.1 SP2) and main.hex file that has to be loaded in to model.

System stores current parameters in Atmega8 internal EEPROM so each time Audio processor is powered it remembers last settings. Parameters are saved to EEPROM after <60 s of last menu inactivity.

Wach video of menu control:

Fully functioning compiled firmware, WinAVR ready source files and Eagle project files can be downloaded here (audioproc.zip). If circuit assembled correctly it should work at once.

Conclusion

Hardware and software seems to be working OK. Signal output was inspected with oscilloscope and with speakers. All functionality works as expected. Audio signal quality on exit depends on power supply stability, be sure to use filtered power supply like for any other audio system.

Dont try to connect speakers or headphones to audioprocessor output – you wont hear anything because output load resistance has to be 2kΩ so pass through some kind of amplifier if you want to hear sound while testing. I have used PC speakers with built in amp.

Recommendations

• Project it self is very easy to replicate. Just build PCB and furn Firmware.hex.

• If you need smaller board, then you should think of double sided PCB.

• Program source isn’t optimized very much – all based on if, else – I think there is many ways to make it more compact and more readable – but maybe next time. Feel free to modify project – just send a note of your version.

Have fun.

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This entry was posted on Thursday, August 9th, 2007 at 12:10 am and is filed under AVR Microcontrollers, AVR controlled audioprocessor, Projects. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.