Goldilocks Analogue

Arduino AVR ATmega1284p Analogue (DAC) Platform

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The Goldilocks Analogue is available on Tindie now.

Based on the orgiginal Goldilocks (ATmega1284p Arduino compatible), the goal is to be able to produce a DC referenced signal analogue signal, from 0Hz up to around 50kHz, that can provide a binary-linear representative voltage (with sufficient current) to enable a control system, as well as to produce the highest quality audio, with very low noise and THD buffer amplifiers, that the basic AVR platform is capable of producing.

Implementation is using MCP4822 dual channel 12 bit DAC, with a TS922A OpAmp producing buffered DC referenced analogue, and a TPA6132A2 headphone amplifier producing an AC referenced stereo audio output.

The latest prototype (in red) has also incorporated a microphone amplifier (including bias circuit for smartphone electret microphones), and a line-in level shift.

Designing an analogue project is a challenge over a digital only project. When laying out the board it is important to consider how digital noise will affect the output, and where signals pass. Asking experts and reading references recommends centralising a separate analogue ground plane or, as I have done, keeping the ground plane solid and keeping digital switching components separate from analogue components.

The process of design has uncovered principals that I didn't know about at the start, such as needing headroom on the supplies for an OpAmp. Rail to rail is a marketing term, that doesn't really exist.

Also, feature creep is a thing. Over the past year I have separated AC and DC biased outputs, added SPI EEPROM or RAM for fast storage, and finally implemented a microphone input circuit. All of which will make the result better, but each one takes an iteration to build and test.

  • 1 × MCP4822 Data Converters / Digital to Analog Converters (DACs)
  • 1 × TS922A Amplifier and Linear ICs / Operational AmplifiersO
  • 1 × TPA6132A2 Headphone Amplifier
  • 1 × 23LC1024 Memory ICs / Static RAM (SRAM)
  • 1 × MB85RS64V Memory ICs / Other Memory ICs

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