In an effort to bring analog capabilities to the Arduino environment, Phillip Stevens has developed a board he calls the Goldilocks Analogue. The Goldilocks Analogue, which was also named a quarterfinalist in this year’s Hackaday Prize, provides Makers with all of the analog audio input and output they could possibly need, together with sufficient data storage options. With this board, Makers will have the ability to delve into the world of digital synthesis, human auditory augmentation, sound activated systems, signal processing and analog process control, among many other things. If the name seems vaguely familiar, that’s because you may recall Stevens from his 2013 project, Goldilocks. Two years ago, the Maker devised an Arduino Uno clone using the ATmega1284P MCU for applications that required more SRAM and Flash memory than what the ATmega328P could support, all without sacrificing the Uno’s footprint. Although his initial efforts achieved its goal, the resulting platform still lacked one function that he believed was a necessity: high-quality analog input and output. “The world is analog, but having an ADC capability without having a corresponding digital-to-analog capability, is like having a real world recorder with no means to playback and recover these real world recordings,” the Maker explains. Fast forward to 2015 and the successor is yet again built around the mighty ATmega1284P. As Steven points out, the external analog output platform has been optimized to provide dual-channel stereo output (up to 48k samples per second) by overclocking the AVR MCU to 24.576MHz. The Goldilocks Analog is equipped with a 12-bit DAC that offers dual-stereo channels with output voltage ranging from 0V to 4.095V, which is fed to both a high-current capable op-amp and a dedicated headphone amplifier. These options enable optimal reproduction of audio, as well as DC level referenced analog 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 256KB SRAM and AT25M01 256KB EEPROM, without any timing constraints,” the Maker writes. Meanwhile, audio input is managed by an AGC microphone amplifier. Gain is adjustable from 40dB (default for typical smartphone headset microphone) up to 60dB, which also lends support to electro-cardio or other high sensitivity applications. Aside from that, he included a level shifted non-amplified signal (for line-in). According to Stevens, the main switched-mode power supply is rated at well over 2A, and is filtered by a second order LC network to provide a clean 5V for the analog platform. Lastly, the Goldilocks Analogue incorporates a 3.3V 1A regulator for the microSD card and 3.3V shields. The negative supply for the op-amp is handled by a -3V inverting charge pump regulator and filtered by a first order LC network. So what can you create with this board? While the possibilities are endless, example projects include a triple oscillator digital synthesizer, a digital walkie-talkie, a sound-sensing alarm and even an Internet-connected baby monitor. And to make all of the analog power easy-to-use, the Goldilocks Analogue is compatible with the Visuino IDE for drag-and-drop signal programming. “Using a smartphone-compatible 3.5mm socket, a microphone input and headphone outputs can connect your sounds into the Arduino world. Samples of sound can be played back from on-board SRAM or recorded onto the EEPROM to be recovered later,” Stevens adds. “Up to a minute of telephone quality audio can be stored (less for higher quality), or played back using the on-board storage. The microSD card can store and play back GB of audio, if desired.”
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