Reading 1-Wire Sensors into Grafana

FIBER only: FIBER Lite has no 1-Wire hub (see What's Different).

FIBER's eight isolated 1-Wire ports appear in Linux as eight independent bus masters, so a probe on port 3 is visible at a different path than one on port 5. Reading them needs no driver setup and no configuration, because the kernel already exposes them.

How the eight ports are wired

The ports are not bit-banged GPIO. They sit behind a DS2482 I2C-to-1-Wire bridge at address 0x18 on bus i2c-10, which the ds2482 kernel module drives. Each physical port gets its own master:

ls /sys/bus/w1/devices/

w1_bus_master1  w1_bus_master2  w1_bus_master3  w1_bus_master4
w1_bus_master5  w1_bus_master6  w1_bus_master7  w1_bus_master8

w1_bus_masterN corresponds to physical port N. The bridge and the ds2482, wire and w1_therm modules are part of the shipped image, so there is nothing to install or enable.

Finding which ports have probes

Every detected sensor also appears as a symlink directly under /sys/bus/w1/devices/, named by its family code and unique ROM ID (28-… is the DS18B20 family):

ls -d /sys/bus/w1/devices/28-*

To see which port each one is on, ask the masters:

for m in /sys/bus/w1/devices/w1_bus_master*; do
  echo "$(basename "$m"): $(cat "$m/w1_master_slave_count") -> $(cat "$m/w1_master_slaves" | tr '\n' ' ')"
done

w1_bus_master1: 0 ->
w1_bus_master2: 0 ->
w1_bus_master3: 1 -> 28-00000bc830e0
w1_bus_master4: 0 ->
...

An empty port reports 0 and lists nothing. A port with a sensor that has gone missing keeps its last known ROM ID but stops updating, see Troubleshooting below.

Reading a temperature

Each sensor exposes a temperature file in milli-degrees Celsius:

cat /sys/bus/w1/devices/28-00000bc830e0/temperature

24625

That is 24.625 °C. Divide by 1000.

The raw w1_slave file gives the same value plus the CRC status, which is what you want when diagnosing a flaky probe or long cable:

cat /sys/bus/w1/devices/28-00000bc830e0/w1_slave

8a 01 4b 46 7f ff 06 10 2c : crc=2c YES
8a 01 4b 46 7f ff 06 10 2c t=24625

crc=2c YES means the reading is trustworthy. A NO means the value on the second line is garbage and must be discarded, not averaged in.

note

Reading these files triggers a conversion on the bus, which takes up to ~750 ms per sensor. The FIBER application is already sampling the same probes every 2 seconds, so keep any polling of your own modest. A few seconds between reads is plenty, and it keeps the bus free for the application that drives the alarms.

Getting the readings into Node-RED

A single exec node is enough, with no contrib package and no extra dependency. Point it at a small shell command and let Node-RED parse the output.

Use an inject node on a repeating interval → an exec node running:

for d in /sys/bus/w1/devices/28-*; do echo "$(basename $d) $(cat $d/temperature)"; done

then a function node to turn the lines into one message per sensor:

// exec output: one "28-<romid> <milli-degC>" line per sensor
var out = [];
(msg.payload || "").trim().split("\n").forEach(function (line) {
    var parts = line.trim().split(/\s+/);
    if (parts.length !== 2) { return; }
    var milli = parseInt(parts[1], 10);
    if (isNaN(milli)) { return; }
    out.push({
        measurement: "onewire",
        tags: { sensor: parts[0] },
        fields: { temperature: milli / 1000 }
    });
});
return [{ payload: out }];

Feed that into an influxdb batch node and the readings land as a onewire measurement tagged by ROM ID, ready to graph.

tip

Tag by ROM ID, not by port number. The ROM ID is burned into the probe, so a sensor keeps its identity in the database even if someone moves it to another port, which is exactly what you want when comparing a week of history.

Storing and visualizing the readings

Node-RED, InfluxDB and Grafana are part of the same shared stack on both variants, see Install Node-RED, Install InfluxDB and Install Grafana. The flow above therefore writes to InfluxDB on the same device, and Grafana reads it back locally.

A time series of temperature grouped by the sensor tag is the usual starting point for a panel.

note

Check that the stack is present before wiring the flow up:

command -v influxd grafana-server node-red

If those come back empty, the unit is running an image built before they were included. Point the flow at another host that has them. FIBER runs Mosquitto, so publishing the readings to MQTT and subscribing from that machine is the path of least resistance.

Troubleshooting

A port shows 0 slaves. Nothing is detected on that physical port. Check the probe's wiring first. 1-Wire needs data and ground, and a parasitic-power probe also needs a pull-up. The ports are isolated from each other, so a fault on one does not disturb the others.

crc=... NO. The sensor answered but the frame was corrupt. Usually cable length, interference, or a marginal connection. Discard those samples rather than averaging them in.

A sensor disappears after being unplugged. The kernel removes the device node once it stops answering. Code that reads a fixed path must tolerate the file vanishing, not crash on it.