Hi, my name is
Alejandro Castillo
Software Engineer
Recent CS graduate from CSUN, building across the full stack — embedded IoT systems and production web apps.
About Me
Building things that matter
I'm a recent Computer Science graduate from Cal State Northridge. I finished my degree in December 2025, with hands-on experience building across the full stack — from bare-metal embedded firmware to cloud-deployed web applications.
My recent projects span IoT systems (ESP32 + FreeRTOS + MQTT), voice AI agents (GPT-4o + Twilio), and production marketing sites deployed for real clients. I gravitate toward work where software meets the physical world or where automation can do something genuinely useful.
Previously at UC Riverside before transferring to CSUN. Outside of code I'm usually exploring new hardware, picking apart how things work, or looking for the next interesting problem to build a solution for.
Work
Featured Projects
Sentinel — IoT Air Quality Monitor
End-to-end IoT system on ESP32 WROVER that samples temperature, humidity, and air quality at 1Hz, smooths data with EMA, and publishes over TLS MQTT to a cloud backend — with zero data loss.
- ▸Bit-bang GPIO driver for DHT22 + I2C driver with CRC8 for SGP30 (cross-sensor humidity compensation)
- ▸3-task FreeRTOS pipeline with mutex-protected queues for acquisition, smoothing, and publishing
- ▸Node.js/TypeScript backend with REST API and SQLite; deployed on Render with GitHub CI/CD
PGAI Voice Bot — Patient Simulator
An automated voice bot that calls an AI medical receptionist, simulates 10 realistic patient scenarios, records and transcribes each call, and identifies edge-case bugs in the agent's behavior.
- ▸10 patient scenarios: scheduling, cancellations, emergencies, Spanglish, pushy callers
- ▸Full audio recording + structured JSON transcript storage per call
- ▸Surfaces hallucinations, policy violations, and missed escalations
Hotsman Construction — Marketing Site
Production marketing website for a local contracting business, designed and deployed end-to-end as a freelance engagement.
- ▸Custom domain, DNS configuration, and Vercel deployment pipeline
- ▸Booking integration and contact workflows
- ▸WCAG accessibility improvements based on client feedback
Toolbox
Skills & Technologies
Languages
- Python
- C / C++
- JavaScript
- TypeScript
- SQL
Frameworks & Libraries
- Next.js
- React
- Node.js
Embedded & Systems
- ESP-IDF
- FreeRTOS
- MQTT / TLS
- I2C / GPIO
- PlatformIO
Tools & Infra
- Git
- VS Code
- Vercel
- Render
- SQLite
Contact
Get In Touch
Open to new opportunities, collaborations, or just a good conversation.