Scienceprog has built an audio processor control board with three selectable stereo inputs and four outputs. The system is built to be a stand-alone device that can be embedded almost in every audio system. Audio-processor is capable of controlling Volume, BASS, Treble, attenuation of each output channel. The TDA7313 is a digital volume and tone control audio processor that can be used in various audio applications, such as in-car audio systems, mini/micro audio systems, and portable audio players. The benefits of using an audio processor like the TDA7313 include: There is very intuitive menu control installed – parameters are changed by inspecting the visual bar in LCD. All Tda7313 functionality is covered with only five buttons. The device can also remember the last parameter settings. So each time it is powered – the last saved parameters are loaded. All project files are available for download, including Eagle project, WinAVR project, and pre-compiled firmware. As for new alternatives to the TDA7313, several newer digital audio processors on the market offer similar functionality, including the Cirrus Logic CS8406 and the Texas Instruments…

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Thomas Pfeifer has connected Nokia 6100 132×132 pixel 4096 color LCD to an AVR microcontroller. LCD is also used in Nokia 6100, 7200, 6610, 7250, and 6220. This display was relatively small by modern standards but was typical for phones of its time. The color depth of 4096 allowed for a range of colors to be displayed, but with limited color accuracy and depth compared to modern smartphone displays. He connected LCD to Atmega8 microcontroller: There are two display types: Epson chipset(S1D15G10) and Philips(PCF8833); The PCF8833 is a graphics display controller designed for color TFT displays with resolutions up to 176×220 pixels. It supported 4096 colors and used a serial interface to communicate with the phone’s main processor. The Epson S1D15G10 was not used in the Nokia 6100 specifically. The example code is written for Philips chipset. Firmware is written in AVR-GCC language, where images can be uploaded via serial cable. Also, there are few video view sample videos on how it AVR-3D-Engine works.

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This AVR DDS generator can generate signals from 1Hz up to 65535Hz. Thanks to well known DDS algorithm, frequency limits can be much higher, but signal resolution drops in higher frequencies. The current range is enough for most audio signal equipment testing. DDS algorithm is written in software where Atmega8 runs at a maximum 16MHz. Several signal waveforms are available: sine, square, sawtooth, triangle, reverse sawtooth and pseudo-random noise.   Signals are stored in lookup tables as the DDS algorithm requires. Signal output is organized via simple R-2R ladder DAC. LCD signal goes through the shift register; this way, only 3 MCU pins are used, while others serve for other purposes – buttons other outputs. The project is well documented PCB and source files included. The author states that he will build another DDS generator with improved control and variable signal amplifier at the output.  

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