Digital Guitar Effects Processor

This project follows my 2022 Multi Effects Guitar Pedal, which used an STM32 Nucleo development board and its internal ADC and DAC. This time, I’m building the audio hardware on a custom PCB.

The processor is designed to run on its own, with an STM32 microcontroller, an external audio codec, analog signal conditioning, and an integrated power supply. A guitar signal enters through the analog input stage, is converted to digital samples by the codec, and is processed by the STM32. The codec then converts the processed signal back to analog for the output stage. Clocking, power regulation, and programming interfaces are part of the board as well.

Putting analog audio circuitry and digital electronics on one PCB makes noise control an important part of the layout. I’m paying particular attention to grounding, power distribution, decoupling, component placement, and the audio signal path. Interference in that path or the supply can be heard in the processed output.

The board is designed for a standard 9 V guitar pedal supply. An on-board switching regulator provides 3.3 V for the digital electronics. I developed and tested the power supply separately before integrating it with the rest of the system; initial measurements showed stable voltage regulation.

An SWD interface lets me program and debug the STM32 directly on the custom PCB during firmware development and hardware testing.

The firmware is intended to stream audio continuously between the codec and STM32, with the effects processed in software in real time. I’m starting with delay and tremolo, building on what I learned from the earlier pedal. More advanced effects are planned for later.

The audio algorithms are kept separate from the hardware interface so I can experiment with DSP techniques without redesigning the electronics.

Work is progressing from power supply validation through microcontroller bring-up and the basic audio hardware. The next steps are to integrate the external codec, establish the real-time audio pipeline, and implement the effects.