The Goldilocks Analogue project was launched yesterday on Kickstarter.
This is a private project (not a for profit company), but Seeed Studio have agreed to put it into their catalogue, should the Kickstarter campaign be successful.
This will ensure that there is an ongoing commercial source for these ATmega1284p Arduino R3 standard boards.
The analogue output platform has been optimised to provide dual channel (stereo) output at up to 48k samples per second. To achieve this sample rate the ATmega1284p MCU is overclocked to 24.576MHz. Choosing this crystal frequency permits the use of an 8 bit timer to accurately (15ppm) generate any sampling frequency that is a factor of 384,000, from 2,000 right up to 48k samples per second. Overclocking the MCU by 22% means that it probably won't work at the extremes of the specified temperature range from -40 Celcius up to +85 Celsius. If overclocking is a problem for you, please don't support this project.
The MCP4822 12bit DAC provides dual (stereo) channels with output voltage range from 0V to 4.095V, which is fed to both a high current capable TS922A Op Amp and a dedicated TPA6132A2 Headphone Amplifier. These options allow optimal reproduction of audio, and DC level referenced analogue outputs.
The DAC is driven by the ATmega1284p USART1 in Master SPI Mode. This frees up the normal Arduino SPI bus to access the MicroSD card, or either of the two on-board SPI interface memory devices, 23LC1024 256kByte SRAM and AT25M01 256kByte EEPROM, without any timing constraints.
Audio input is managed by a MAX9814 AGC Microphone amplifier. Gain is adjustable from 40dB (default for typical smartphone headset microphone) up to 60dB, which also lends support electro-cardio or other high sensitivity applications too. Additionally, a level shifted line-in is provided to support AC line level signal input. These signals are connected to the Arduino A7 and A6 pins respectively, and can be sampled by the integrated AVR 10bit 15k samples per second ADC capability.
The main AP6503 SMPS power supply is rated at well over 2A, and is filtered by a 2nd order LC network to provide clean 5V for the analogue platform. The Goldilocks Analogue also incorporates a CJA1117 3.3V 1A regulator for the MicroSD card, and 3.3V shields. The negative supply for the Op Amp is provided by a LTC1983 -3V inverting charge pump regulator and it is filtered by a 1st order LC network.