DARCY
JOHNSON

STM32 Embedded Controller

An exploration into 4-layer PCBs, galvanic isolation, strict EMI filtering, and mixed-signal design to create a robust, industrial-style controller.

Powered by an STM32, the board handles galvanically isolated field I/O using a custom DMA-driven MODBUS RTU stack. It also features a "no-code" automation engine, letting you configure logic remotely via a web panel.

To ensure system reliability, I integrated an efficient power supply with fault protection, an OLED display for local feedback, power monitoring, and EEPROM storage.

The entire ecosystem: custom PCB, schematics, firmware, and the web panel - is completely open-source on GitHub. Check out the datasheet for a deep dive!

TouchTone555 Stylus Synth

An exploration into analog synthesis, noise filtering, signal modulation, and amplification.

Utilising the NE555 timer IC, I created a stylophone inspired stylus synth from scratch, featuring 4-switchable octaves, vibrato, an on-board amplifier, and individually tuneable keys.

Designed with a "modularised" silkscreen, the custom PCB shows how many different parts or sub-blocks work together in an analog circuit.

I released the project fully Open Source on GitHub, providing instructional documentation to several builders worldwide!

An early-stage project exploring the design and construction of a purely mechanical relay computer based on a Harvard architecture.

Development Roadmap

Phase 1: Architecture Design & Prototyping (Current)
Researching and outlining the desired architecture - Harvard-based RISC, rather than Von Neumann, with an 11-bit program RAM and an 8-bit data RAM. Prototyped the 6-bit program counter (PC) with a minimal viable circuit physically, then expanded to the full 6-bits in custom simulation software.

Phase 2: PCB Design
Transitioning from benchtop prototyping and simulation towards a working backplane and expansion cards. A slot agnostic backplane will be designed with all required buses exposed so any expansion card can plug into any slot.

Phase 3: Physical Construction & Testing
Construct the minimal viable physical model with minimal program and data RAM, then expand with further expansion cards. Test basic programs written for this computer's RISC instruction set.

End Goal:
Build a fully discrete electromechanical computer capable of loading and running a playable game of Snake from physical punchcards onto a custom 8x8 relay-driven VDU at a playable refresh rate.

Rules: Zero semiconductors can be used for logic/computation - silicon/semiconductors is strictly restricted to passive flyback coil suppresion diodes and for LED outputs. Everything else is done by electromechanical contacts!