A distributed WiFi reconnaissance system using ESP32-S3 nodes and an Orange Pi as coordinator.
Each ESP32 node scans the WiFi environment, builds structured events (not raw data), and ships them over UDP to a coordinator. The coordinator stores events to SQLite. A separate web dashboard reads the database and displays everything in real time via SSE.
This is a learning/research project covering distributed systems, event-driven architecture, sensor fusion, and detection engineering concepts.
The two coordinator processes are intentionally separate. The ingestor has one job: receive UDP, write to DB. The dashboard has one job: read DB, serve UI. They communicate only through the database. Each is independently restartable without affecting the other.
---
## Development workflow
**All coding is done on this PC.** The Orange Pi only runs the deployed files — never edit directly on it.
│ ├── udp_ingest.service # systemd service file for ingestor
│ ├── dashboard.service # systemd service file for dashboard
│ └── events.db # SQLite database — on Orange Pi only, not synced
├── deploy.sh # rsync script: this PC → Orange Pi
├── starting_plan.md # Original architecture design doc
└── README.md # This file
```
---
## Firmware
Each node:
- Connects to WiFi `sandbox`
- Scans for nearby APs every 15 seconds (active scan, includes hidden SSIDs)
- Captures probe request frames passively (promiscuous mode) between scans
- Sends a heartbeat packet every 10 seconds (uptime, free heap, WiFi RSSI to router)
- Sends beacon, probe, and heartbeat events as UDP JSON packets to the coordinator
-`node_id` is derived from bytes 2–5 of the ESP32's base MAC address
### Event formats
**Beacon event** (AP discovered):
```json
{
"node_id":"F68D6E30",
"ts":12345,
"type":"beacon",
"conf":"high",
"imp":"normal",
"ssid":"NetworkName",
"bssid":"AA:BB:CC:DD:EE:FF",
"rssi":-65,
"ch":6,
"enc":"WPA2"
}
```
**Probe event** (client device searching for a network):
```json
{
"node_id":"F68D6E30",
"ts":12345,
"type":"probe",
"conf":"high",
"imp":"normal",
"src_mac":"AA:BB:CC:DD:EE:FF",
"ssid":"HomeNetwork",
"rssi":-55
}
```
**Heartbeat event** (node health, sent every 10 seconds):
```json
{
"node_id":"F68D6E30",
"ts":12345,
"type":"heartbeat",
"uptime_ms":123456,
"free_heap":245000,
"wifi_rssi":-62
}
```
-`imp`: `high` if RSSI >= -50, `low` if <= -80, else `normal`
-`ssid` in probe events is the network the device is searching for — empty means wildcard (any network)
- Probe dedup: same MAC+SSID suppressed for 30 seconds to avoid flooding
-`wifi_rssi` in heartbeat is the node's own signal to the `sandbox` AP (not a scanned network)
- A node is considered **online** if a heartbeat arrived within the last 30 seconds; falls back to beacon within 60 seconds if no heartbeat has been received yet
### Flashing a node
Requirements: Arduino CLI v1.4.1, ESP32 core v3.3.7, FQBN `esp32:esp32:esp32s3`, user in `dialout` group.
Service files are in `coordinator/` and deployed to `/etc/systemd/system/` on the Orange Pi.
The coordinator files live at `/opt/esp32_cluster/coordinator/` on the Orange Pi.
---
## Dashboard
Open `http://192.168.1.133:8080` in your browser.
### Views
- **Feed** — live beacon event stream across all nodes, capped at 100 rows, newest on top
- **Networks** — deduplicated AP table (by BSSID): times seen, best/avg RSSI, channel, encryption, node count. Sortable by any column. Each row has a ▶ button to open the RSSI history chart for that network.
- **RSSI history chart** — opens from any Networks row. Shows signal strength over time per node (1h / 2h / 6h / 24h selectable). Each node gets its own coloured line. Useful for spotting interference patterns, seeing how signal fluctuates by time of day, and comparing which node consistently hears a given AP better. Updates live as new scans arrive.
- **Cross-node** — side-by-side per-node RSSI for every AP. Shows which node is physically closer to each network. Filter to multi-node only to focus on confirmed cross-node observations.
- **Clients** — probe request data: unique MACs, vendor (OUI lookup), what SSIDs they're searching for, signal, which nodes saw them.
- **Node detail** — click a node in the sidebar for stats: total events, unique SSIDs/BSSIDs, RSSI range, first/last seen, uptime, free heap, AP signal, last 100 events.
### Sidebar
Always visible: node list with online/offline status dot, last seen time, event count, and a compact heartbeat line (uptime · free heap · AP signal).
A node is considered **online** if a heartbeat was received within the last 30 seconds. Falls back to beacon timestamp (60s threshold) if no heartbeat has been received yet.
SSE stream pushes new beacon events as they arrive. The feed updates immediately. All other views (sidebar, networks, chart, cross-node, presence) refresh on a 2-second debounce so a single scan burst doesn't flood the server with requests.
Networks with a blank SSID but valid BSSID, signal, and channel are **hidden networks** — APs configured not to broadcast their name. They are not hidden from passive scanners. The encryption showing as `OPEN` is a firmware parsing artifact; the network itself may be encrypted. The BSSID OUI still identifies the manufacturer.
### Probe requests and MAC randomization
Modern phones and laptops (iOS since ~2020, Android since ~2021) randomize their MAC address for probe requests. A randomized MAC has bit 1 of the first byte set — the dashboard detects this and labels it "Randomized MAC" instead of doing a meaningless OUI lookup.
What probe data tells you:
- **Directed probes** (with SSID): the device has connected to that network in the past
- **Wildcard probes** (empty SSID): the device is searching for any available network
- Probe data maps **client devices**, not infrastructure — complementary to beacon scan data
### OUI lookup
The `oui.txt` file is the IEEE public OUI database (39,171 entries as of download). It maps the first 3 bytes of a real MAC to a manufacturer name. Used in the Clients tab. Refresh it occasionally by re-running `deploy.sh` after downloading a fresh copy from `https://standards-oui.ieee.org/oui/oui.txt`.
