Cathal Coffey

Staff Software Engineer & Physical Systems Builder

Based in Dublin, Ireland. Over a decade designing, scaling, and operating mission-critical distributed systems, developer platforms, and computational engines across companies spanning every order of magnitude: Equals (~10), Intercom (100 → 1,000+), HubSpot (~8,000), and Amazon (150,000+).

Beyond cloud infrastructure, I am a hands-on physical computing builder: designing custom microcontrollers (ESP32-C5, ATtiny), robotics, motor drive electronics, time-of-flight laser sensor networks, CAD/CNC fabrication, and mathematical energy storage optimization.

GitHub: @ccoffey LinkedIn coffey.cathal@gmail.com

🛠️ Personal Projects & Physical Systems

Hands-on hardware, robotics, embedded firmware, clean energy, and physical computing built from first principles.

Chimera Handheld

A bespoke, minimalist handheld mobile device inspired by the tactile industrial design and durability of the Nokia 3210.

  • SoC: ESP32-C5 (32-bit RISC-V core with dual-band 2.4/5 GHz Wi-Fi 6 & BLE 5).
  • Peripherals: SSD1309 OLED display, MAX98357A I2S Class D DAC, INMP441 MEMS microphone.
  • Firmware: Native ESP-IDF C/C++ managing ultra-low-power sleep states, matrix keypad scanning, and custom CMake build tooling.
ESP32-C5 RISC-V ESP-IDF Embedded C/C++ I2S Audio Hardware Design
Magic Stairs

Interactive architectural staircase illumination system that senses movement and triggers responsive dynamic animations ("rainbow run") for my kids.

  • Two-Tier Distributed Network: Central ESP32-WROOM-32 orchestrator + individual ATtiny414 microcontrollers per step.
  • Bus Decoupling: Solved single-address VL53L0X Time-of-Flight (ToF) sensor hardware constraint via bit-banged I2C masters on ATtiny nodes.
  • Autonomous Indexing: WS2815 LED data line sniffing to deduce physical step riser positions on boot without DIP switches.
ATtiny414 ESP32 VL53L0X ToF I2C Bit-Banging WS2815 LEDs Distributed IoT
Autonomous Veranda Bot

High-risk outdoor cleaning robot engineered to navigate and clean the high-elevation, sloped glass roof of a garden veranda where human maintenance is dangerous.

  • Actuation & Power: Dual BTS7960 43A H-Bridge motor drivers for differential drive; dedicated MOSFET switch for scrubbing head.
  • Radio Control: ESP-IDF component decoding 9-channel Turnigy TGY-9X RC PWM pulses using microsecond-precision hardware interrupts.
  • Fail-safes: Signal loss watchdog, thermal motor limits, and differential steering kinematics.
Robotics ESP32 BTS7960 H-Bridge Turnigy RC PWM FreeRTOS Electro-Mechanical
Solar & Storage Orchestrator

Closed-loop clean energy forecasting and scheduling system optimizing a 10.12 kWp dual-aspect PV array, 18.08 kWh battery, Wallbox EV charger, and Tesla.

  • Telemetry Ingestion: Interfaces with SigenStor/SigenCloud APIs, local Modbus/TCP registers, and solar irradiance forecasts.
  • MILP Optimization: 24-hour lookahead Mixed-Integer Linear Programming model that evaluates dynamic wholesale electricity tariffs to calculate globally cost-optimal battery and EV charging schedules.
  • Vehicle Telemetry: Real-time integration with Tesla Fleet Telemetry API for dynamic throttling (1.38–7.36 kW).
MILP Optimization Python Clean Energy Modbus/TCP Tesla API Time-Series
Arcade & Claw Machines

Custom-engineered physical gaming hardware: from custom PCBs and silent stepper motor drivers to millimeter-tolerance CAD/CNC control panels.

  • Claw Machine: Custom KiCad PCB, Trinamic TMC2209 stepper driver over single-wire UART (stealthChop2, stallGuard), custom AnalogMultiplexor library, and Flask/WebSocket telemetry dashboard.
  • Arcade Control Panel: Parametric CAD layout generator in Python with absolute millimeter coordinates for zero-tolerance CNC drilling; multi-band image blending for high-DPI acrylic marquee artwork.
KiCad PCB TMC2209 UART CNC / CAD Arduino Computer Vision Fabrication
Real-Time Chat Backend

Concurrent, high-performance messaging backend service with sub-millisecond persistence and instant push notification dispatch.

  • Stack: Java 24, Spring Boot, MySQL 8.0, Maven.
  • Mobile Push Notifications: Integrated Firebase Cloud Messaging (FCM) Admin SDK for real-time alert delivery to mobile clients.
  • APIs: Concurrent RESTful endpoints for user provisioning, message pagination, and bi-directional message synchronization.
Java 24 Spring Boot MySQL 8.0 Firebase FCM REST APIs

🏢 Career Highlights

Engineering leadership and distributed systems architecture across startups, hypergrowth, and hyperscale tech.

Staff Software Engineer — HubSpot (Flywheel Org)
June 2024 – Present | Dublin, Ireland
  • LookAlikes Prospecting Engine: Architected automated opportunity generation engine analyzing closed-won customer attributes to automatically uncover and provision high-affinity enterprise prospects not yet in the CRM, directly generating closed sales.
  • Curated Sales View (Collaborative Filtering): Eliminated CRM data fatigue by engineering a 3-rep dismissal collaborative filter and defaults based on top 10% performers, driving near-total migration from the legacy CRM view.
  • Company Hierarchy & Entity Resolution: Solved complex sales territory disputes by crawling parent/subsidiary disclosures and analyzing account overlaps to build deterministic hierarchy graphs.
  • Org-wide RFC Culture & Technical Standards: Authored standardized Technical Design templates and ran workshops across teams, raising architectural rigor and code review quality.
Software Engineer — Equals (Core Engine Team)
January 2023 – March 2024 | Series A Startup (~10 people)
  • Core Computational Engine & Dependency DAG: Core engineer on 3-person engine team; optimized formula dependency graph evaluation (DAG propagation) using B-trees and skip lists to calculate minimal dependent cell updates without UI thread locks.
  • WebSocket State Catch-Up: Designed client delta synchronization over WebSockets to seamlessly catch up state when client laptops wake from sleep.
  • Engine Port & Connectors: Built secure SSH database connectors for live queries (Postgres, Snowflake) and led runtime migration from Rust-Wasm to high-performance TypeScript.
Staff Engineer • Senior Engineer • Engineer — Intercom
December 2015 – December 2022 (7 yrs 1 mo) | Dublin, Ireland
  • Lead Architect on Project Europe: Served as lead technical architect on a 3-person Skunk Works team transitioning Intercom from a 13-year single AWS region to multi-region deployments in Europe and Australia, unblocking major enterprise contracts requiring EU data residency.
  • Cross-Org Billing Decoupling: Architected multi-region routing for Intercom's standalone billing service; designed global App/Admin ID namespaces and automated US/EU invoice bake-off testing ensuring zero billing discrepancies on Day 1.
  • CI/CD Bin-Packing Optimization: Analyzed runtime histograms of 45,447 tests across 30 CI containers; implemented bin-packing test distribution, saving 2,000 engineering minutes per day across ~100 daily production deploys.
  • Founding Engineer, Team Datastores: Served as interim EM and Tech Lead; resolved upstream Elasticsearch bug with Elastic Principal Engineers, unblocking a zero-downtime upgrade spanning 54 releases.
  • Contrail Cold Storage: Re-architected a 42-billion-row (60TB) append-only DynamoDB event store under strict 6-week SOC2 deadline, eliminating throttling and saving $144k/year.
  • Real-Time Systems & Machine Learning: Consolidated real-time WebSocket infrastructure into nexus-go; built ML binary classifier (Merlin) boosting article recommendation precision.
Software Development Engineer (SDE) — Amazon
March 2014 – October 2015 | Dublin, Ireland
  • Engineered real-time streaming log enrichment platform processing, storing, and indexing millions of temporally evolving unique entities updated every second using AWS Kinesis, DynamoDB, SQS, Spark, Java, and Scala.
  • Handled Tier-1 24/7 operational on-call rotations, configured deep metric alarms, and authored operational runbooks.

🌐 Open Source & Research

  • GitHub gh-ost (PR #921): Diagnosed and resolved critical production failure mode in MySQL online schema migrations timing out during atomic cut-over under heavy write load. Engineered CurrentHeartbeatLag in Go to gate cut-over until binlog lag dropped below safety thresholds.
  • DocX (github.com/xceedsoftware/DocX): Created popular open-source .NET library for Word document manipulation without Office dependencies; surpassed 100,000+ downloads.
  • IBM Smarter Cities Technology Center (2011, 2012): Researched multimodal transit synchronization algorithms; published peer-reviewed papers at IEEE MDM 2012 (Missed Connections) and ACM SIGSPATIAL 2011 (Predictability Horizons).
  • Academic Background: Ph.D. Candidate at UC Berkeley (CEE Systems, ML, 2014) • M.Sc. in Machine Learning & Geocomputation at NUI Maynooth • B.Sc. (Honours) in Computer Science at NUI Maynooth (Intel Medal for Best CS Student, 2010).