MQTT Output
ESPGeiger uses MQTT to publish radiation data from your Geiger counter. This section details its interaction with MQTT brokers.
- ESPGeiger transmits radiation statistics every minute. This can be configured.
- By default, it connects to the MQTT broker on the standard port
1883 - ESPGeiger publishes data to a base topic named:
ESPGeiger‑<device_id>
Published Topics
Primary topics (JSON)
| Topic | Description | Publish Interval Default |
ESPGeiger-<device_id>/tele/lwt | Last Will and Testament. Online on connect, Offline via LWT on disconnect. | event |
ESPGeiger-<device_id>/tele/sensor | Radiation measurements bundle (CPM, uSv, CPS, CPM5, CPM15, HV, warn, alert). | 60 s |
ESPGeiger-<device_id>/tele/status | Device state + diagnostics (time, uptime, IP, RSSI, counts, load metrics, memory, serial health on serial builds). | 60 s |
Event topics
| Topic | Description | Example | Publish Interval |
ESPGeiger-<device_id>/stat/WARN | Triggered when CPM crosses the warning threshold. | 0 / 1 | edge-triggered |
ESPGeiger-<device_id>/stat/ALERT | Triggered when CPM crosses the alert threshold. | 0 / 1 | edge-triggered |
Legacy per-metric topics (backward compat)
Planned for removal in a future release — prefer consuming tele/sensor JSON instead.
| Topic | Example | Interval |
ESPGeiger-<device_id>/stat/CPM | 30.00 | 60 s |
ESPGeiger-<device_id>/stat/CPM5 | 28.50 | 60 s |
ESPGeiger-<device_id>/stat/CPM15 | 29.10 | 60 s |
ESPGeiger-<device_id>/stat/uSv | 0.20 | 60 s |
ESPGeiger-<device_id>/stat/CPS | 0.50 | 60 s |
ESPGeiger-<device_id>/stat/HV | 412.00 | 60 s (ESPGeiger-HW only) |
Example tele/sensor JSON
{"cpm":87.00,"usv":0.51,"cps":1.45,"cpm5":149.76,"cpm15":212.07,"warn":1,"alert":0}
| Field | Description |
cpm | Current CPM |
cpm5 | 5-minute smoothed CPM |
cpm15 | 15-minute smoothed CPM |
usv | μSv/h (cpm × ratio) |
cps | Counts per second |
hv | HV reading (ESPGeiger-HW only) |
warn | 1 when CPM is above configured warning threshold |
alert | 1 when CPM is above configured alert threshold |
Example tele/status JSON
{"time":"2026-04-18T14:52:52Z","ut":120,"board":"ESP-12E","model":"ESPGeiger-Log","ssid":"MyWiFi","ip":"192.168.1.166","rssi":-37,"c_total":165,"tick":953,"t_max":4870,"lps":58733,"free_mem":16928}
| Field | Description |
time | Current device time (ISO 8601 UTC, with Z suffix) |
ut | Uptime in seconds |
board | ESP chip model |
model | Configured Geiger model |
ssid | Connected WiFi SSID |
ip | Device IP address |
rssi | WiFi signal (dBm) |
c_total | Total clicks since boot |
tick | EMA-smoothed sTickerCB duration (μs) — device load signal |
t_max | Peak tick in last 60 s |
lps | Loop iterations per second |
free_mem | Free heap (bytes) |
ser_ok | 1 when the external serial counter has sent a valid line within the last 60 s, 0 otherwise. Serial builds only — absent from pulse builds. |
ESPGeiger