NJT Audio

Embedded systems design (STM32, C) + mixed-signal PCB 

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This is a complete concept-to-delivery project involving hardware design, PCB layout, firmware development, basic mechanical design, and rapid iterative feature development based on user feedback. This device targets the audio technology sector, primarily for use with electric guitars and synths. The component placement and track routing for this mixed-signal PCB required special consideration to correctly separate analog and digital regions of the design.

 

At the heart of the design is a 48kHz, 24-bit digital stereo audio signal processor, running on a high-performance STM32 microcontroller. Analog input audio is buffered through a differential input stage, and then converted to I2S serial interface protocol. Signal digitisation and reconstruction is achieved with a dedicated codec — a bidirectional analog-to-digital / digital-to-analog converter optimised for audio applications. The codec is controlled by the main MCU via standard I2C.  

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To facilitate computationally intensive audio effects algorithms, the main PCB includes 8MB of external PSRAM memory, interfaced with the main controller via dual Quad-SPI at >100MHz clock speed. An 4Mbit external SPI flash memory is also included for saving effects parameters, runtime configurations, and safeguarding firmware updates via USB.