Hello. I manage a guest house, 12 rooms, and I’m new to all of this, so please be patient with me.
I want temperature, humidity and door sensors in each room, plus a geyser temperature. My nephew suggested this layout and I’d like to know if it is sensible before I buy everything:
ESP8266 node per room (DHT22 + reed switch)
| Wi-Fi, MQTT
Raspberry Pi 4 in the office (Mosquitto + Node-RED)
| internet
Hermetry (dashboards, alarms to my phone)We get load shedding most weeks, so the internet goes down for 2 to 4 hours at a time. I don’t want to lose readings then. Later I may want to switch the geysers off from the dashboard. Is this feasible and flexible, or is the Pi in the middle a mistake?
Feasible. Put the Pi and the router on a small UPS though, otherwise the Pi buys you nothing during load shedding.
We run nearly this at a few small pump stations, so a couple of things from that.
The Pi in the middle is a good call because of your outages. Have it act as a gateway: one device in Hermetry marked “This device is a gateway”, and each room becomes a child device the first time the Pi reports it. Node-RED collects the room messages from Mosquitto, keeps them in a file or a small SQLite table while the internet is down, and then sends them on with their own timestamps:
topic v1/gw/telemetry
{"Room 4": [{"ts": 1793000000000, "values": {"temperature": 22.1, "humidity": 51, "door_open": 0}},
{"ts": 1793000300000, "values": {"temperature": 22.0, "humidity": 51, "door_open": 1}}]}Make sure the Pi has the right time (NTP after boot) before you put a ts on anything. A big backlog drains a bit slower because replays have their own rate limit on the profile, that’s normal.
Geyser switching can go through the same Pi. A command sent to a child device comes down to its gateway on v1/gw/rpc, so Node-RED subscribes to that and passes it on to the right room. Or make the geyser controller its own device that connects to Hermetry directly. For a geyser I’d go direct, fewer moving parts.
Gateway topics are described in Devices behind a gateway.
Thank you both. Bought the UPS, the Pi has been running as the gateway for two weeks. Last Tuesday we had 4 hours off and the room charts filled in afterwards with no gap. The first try made a “Generic child” profile for every room, then I learned to send a “type” on connect. The geyser controller will be its own device.
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