POC zigbee temp sensors

HOWTO.md

@@ -324,3 +324,132 @@ change, rather than continuously. The SNZB-02P publishes `temperature` in °C
 and `humidity` as a percentage.
 
 Reference: [Zigbee2MQTT MQTT topics](https://www.zigbee2mqtt.io/guide/usage/mqtt_topics_and_messages.html)
+
+## 7, reading with curl
+```bash
+curl --silent --max-time 2   "mqtt://192.168.178.247/$topic" | dd bs=1 skip=$((2 + ${#topic})) status=none
+{"battery":100,"humidity":56.3,"humidity_calibration":0,"temperature":27.1,"temperature_calibration":0,"update":{"installed_version":8704,"latest_release_notes":null,"latest_source":"https://raw.githubusercontent.com/Koenkk/zigbee-OTA/master/images/Sonoff/snzb-02p_v2.2.0.ota","latest_version":8704,"state":"idle"}}
+```
+
+## 8. Store six sensors in RRD files and create graphs
+
+Zigbee2MQTT must retain each sensor's state so the collector can obtain the
+latest reading without waiting for a sleeping sensor:
+
+```yaml
+device_options:
+  retain: true
+```
+
+Install RRDtool and create a Python virtual environment in this project:
+
+```bash
+sudo apt install -y rrdtool python3-venv
+cd "$HOME/service_zigbee"
+python3 -m venv .venv
+.venv/bin/pip install -r requirements.txt
+```
+
+Edit the supplied `config.yaml`. MQTT settings, collection timing, storage
+paths, logging, all six sensors, RRD archives, and graph presentation are
+configured in this one file. Replace all five `CHANGE_ME` topics with the
+friendly names shown by Zigbee2MQTT:
+
+```bash
+nano config.yaml
+```
+
+By default, the databases are written to `/var/lib/rrd` and the generated
+graphs to `/var/www/html/sensors`. Create those directories and grant the user
+running the collector ownership:
+
+```bash
+sudo install -d -o "$USER" -g "$USER" /var/lib/rrd
+sudo install -d -o "$USER" -g "$USER" /var/www/html/sensors
+```
+
+Both paths can be changed under `storage` in `config.yaml`:
+
+```yaml
+storage:
+  data_directory: /var/lib/rrd
+  graph_directory: /var/www/html/sensors
+```
+
+Test one collection cycle:
+
+```bash
+.venv/bin/python read_temperature.py --once
+```
+
+The script creates one RRD file per sensor in the configured data directory and
+three PNG files per sensor in the configured graph directory:
+
+- `*_day.png` covers the last 24 hours.
+- `*_month.png` covers the last 31 days.
+- `*_two_years.png` covers the last two years.
+
+Each graph contains a filled temperature area, a solid humidity line, and a
+dotted battery line. Initially, most of each graph is blank because no historic
+samples existed before the RRD was created.
+
+The collector also generates `/var/www/html/sensors/index.html`. It displays
+six graphs at a time and has controls for switching between the daily, monthly,
+and two-year periods. It remembers the selected period and refreshes the PNGs
+at the interval configured under `html.refresh_seconds`.
+
+With a web server serving `/var/www/html`, open:
+
+```text
+http://RASPBERRY_PI_IP/sensors/
+```
+
+The page settings are configurable in `config.yaml`:
+
+```yaml
+html:
+  filename: index.html
+  title: Zigbee sensor history
+  default_period: day
+  refresh_seconds: 600
+```
+
+RRD structure settings are used only when each `.rrd` file is first created.
+Changing `rrd.step_seconds`, data sources, or archives does not rewrite an
+existing database; preserve or remove the old RRD deliberately before creating
+a replacement.
+
+Run the ten-minute collection loop in the foreground with:
+
+```bash
+.venv/bin/python read_temperature.py
+```
+
+To run it automatically as a user service, copy the supplied service file. It
+assumes this repository is located at `$HOME/service_zigbee`:
+
+```bash
+mkdir -p "$HOME/.config/systemd/user"
+cp zigbee-rrd.service.example "$HOME/.config/systemd/user/zigbee-rrd.service"
+systemctl --user daemon-reload
+systemctl --user enable --now zigbee-rrd.service
+sudo loginctl enable-linger "$USER"
+```
+
+Inspect its status and live logs with:
+
+```bash
+systemctl --user status zigbee-rrd.service
+journalctl --user -u zigbee-rrd.service -f
+```
+
+Graphs can be regenerated without collecting a new MQTT reading:
+
+```bash
+.venv/bin/python read_temperature.py --graph-only
+```
+
+References:
+
+- [RRDtool database creation](https://oss.oetiker.ch/rrdtool/doc/rrdcreate.en.html)
+- [RRDtool graph elements](https://oss.oetiker.ch/rrdtool/doc/rrdgraph_graph.en.html)