Accellum
An IoT operations platform that turns MQTT card and gateway signals into device health, checkpoints, access history, and live dashboards.
Turns noisy Bluetooth signals into reliable entry, exit and live occupancy.
- Role
- Full stack and deployment
- Ownership
- Project owner, end to end
- Core stack
- TypeScript · Nuxt.js · Vue.js · NestJS · MQTT
BLE gateways report every card they hear several times a second. Raw detections flicker, so they can't be used as attendance records directly.
What I built
I owned Accellum end to end, from the MQTT topic design to the Docker Compose stack.
- Designed the MQTT topic scheme for monitor, checkpoint and device-status events, with a last-will message so offline gateways are visible
- Turned flickering BLE detections into reliable records: a 5 s debounce per card and device before an entry or exit is committed, and a 30 s presence timeout swept every minute
- Pushed live occupancy per building to the Nuxt admin over Socket.IO, while PostgreSQL keeps the auditable history
- Built a gateway simulator CLI that publishes DTO-valid KBeacon payloads, so the debounce and timeout logic can be tested end to end without hardware
- Packaged the stack as health-checked Compose services (PostgreSQL, Mosquitto, MinIO, migrations, seed, API, admin) that start in the right order with one command
How it fits together
Cards advertise over Bluetooth LE. Gateways publish what they hear to Mosquitto. A NestJS MQTT microservice validates each payload, resolves the device and card, applies the monitor or checkpoint rules, writes the record through TypeORM, and broadcasts the new count over Socket.IO.
Outcome
Admins see live room occupancy and a clean entry and exit history instead of raw MQTT messages.
Deep diveCore feature walkthroughAn interactive flow of the hardest workflow, step by step.
How the main product workflows operate
Radio observations become durable room presence and access history
Accellum separates physical detection, event transport, domain rules and operator presentation. MQTT keeps devices independent from request-response APIs, while PostgreSQL and WebSocket serve different durability and immediacy needs.
BLE → gateway → MQTT → NestJS → PostgreSQL / Socket.IO
Socket.IO improves freshness; PostgreSQL remains the auditable source for reports and investigation.
Monitor and checkpoint devices intentionally use different session rules instead of sharing one ambiguous timeout algorithm.
A gateway simulator publishes DTO-valid KBeacon payloads every second, so the debounce and timeout rules run end to end on a laptop.
Deep diveFrom BLE card to dashboardThe physical path and the monitor / checkpoint decision logic.
How a card detection becomes attendance data
The card only broadcasts its identity. The gateway turns that radio observation into an application event; the backend then validates, interprets, stores, and publishes the result to operators.
Two detection modes, two session strategies
Monitor mode models presence from repeated signals and checks out on timeout. Checkpoint mode models an entry/exit session with a five-second debounce and explicit room-transfer handling.