LoRaWAN to BACnet: Bridge Wireless Sensors into a BMS

The chain has four stages: the sensor sends an uplink, a gateway forwards it to ChirpStack, ChirpStack decodes the payload and publishes it over MQTT, and the bridge turns the decoded values into BACnet objects. The prerequisite for the bridge to do anything useful is a working ChirpStack payload decoder on the device profile, because the bridge reads the clean object field, not the raw hex.

The most transparent bridge is Node-RED. It subscribes to the ChirpStack MQTT topic, reads msg.payload.object, and pushes each value into a BACnet object. A small flow looks like this:

[ mqtt in: application/+/device/+/event/up ]
        │
        ▼
[ json ]  →  parse the ChirpStack event
        │
        ▼
[ function: map to BACnet points ]
        │
        ▼
[ bacnet out ]  →  write Analog/Binary/Multi-state values

The function node turns the decoded object into the points the BMS will read. The instance number is derived from the device so each sensor occupies a stable, non-overlapping block of object instances:

// msg.payload is the decoded ChirpStack event
var obj = msg.payload.object;
var devEui = msg.payload.deviceInfo.devEui;

// stable per-device offset (e.g. from a lookup table)
var base = deviceInstance[devEui] || 0;   // e.g. 100, 200, 300...

var points = [
  { type: "analogValue", instance: base + 0, value: obj.temperature, name: "temperature" },
  { type: "analogValue", instance: base + 1, value: obj.humidity,    name: "humidity" },
  { type: "analogValue", instance: base + 2, value: obj.co2,         name: "co2" }
];

// drop undefined values so the BMS never reads a stale point
msg.payload = points.filter(function (p) { return p.value !== undefined; });
return msg;

The open-source LoRaBAC flow follows the same idea but with a JSON configuration that maps each payload field to a BACnet object and derives the instance number per device. It acts as a BACnet client and writes into an existing controller on each uplink, which keeps the BACnet traffic low. A gateway-resident bridge (for example Node-RED on a Milesight UG65) usually does the opposite: it runs a small BACnet server so the BMS discovers it as a native device and polls it over BACnet/IP.

Bridging is not strictly read-only. A BACnet write (a new setpoint on a WT102 thermostatic valve, for example) can become a LoRaWAN downlink. The catch is LoRaWAN timing: a Class A device only receives in the short window after its next uplink, while a Class C device receives in near real time. Schedules, setpoints and occupancy modes work well, but the BMS cannot expect instant actuation across a battery-powered fleet. The bridge enqueues the downlink on application/{ApplicationID}/device/{DevEUI}/command/down.

We run ChirpStack and the BACnet bridge as one managed stack on European infrastructure: the decoder on the device profile, the MQTT integration, the bridge middleware and the object mapping. The BMS integrator receives a clean BACnet device with documented, stable points instead of a pile of radio payloads. Talk to us about ChirpStack managed hosting with the bridge included.