Symptoms
- SensorStat card shows "No data"
- Sensor reading is frozen at an old value
- Sparkline shows a flat line or gaps
Diagnostic Steps
1. Check the Device Status
Is the Pi online? Check the device health panel. If the device is offline, see Device Offline first.
2. Verify the Flow is Deployed
Open the Configurator and check the deploy status:
- Deployed (green) — Flow is running, move to step 3
- Not deployed — Click Deploy to push the flow to the Pi
- Failed — See Deploy Failures
3. Check Physical Wiring
Verify the sensor is correctly connected to the Pi:
- DS18B20 (1-Wire) — Data pin to GPIO 4, pull-up resistor (4.7k ohm) between data and 3.3V
- I2C sensors — SDA to GPIO 2, SCL to GPIO 3, correct voltage (3.3V or 5V)
- UART sensors — TX to RX and RX to TX (crossed), correct baud rate
4. Verify Hardware Detection
SSH into the Pi and check if the hardware is detected:
1-Wire:
ls /sys/bus/w1/devices/You should see device IDs like 28-xxxxxxxxxxxx.
I2C:
i2cdetect -y 1You should see the sensor's I2C address in the grid.
UART:
ls /dev/ttyS0 /dev/ttyAMA0The serial port should exist.
5. Check Node-RED Logs
Inspect the Node-RED logs for sensor errors:
sudo journalctl -u nodered --since '5 min ago'Look for:
- Read timeouts
- Invalid data format errors
- GPIO permission errors
6. Verify RTDB Path
The sensor must publish to the correct RTDB path that the dashboard subscribes to:
/devices/{deviceId}/rooms/{roomName}/sensors/{sensorName}
If the path does not match, the dashboard will not receive the data. Redeploy the flow from the Configurator to ensure paths are correct.
7. Check Sensor Calibration
If the sensor reports data but the values seem wrong:
- Open the sensor calibration wizard from the SensorStat card
- Check if an incorrect calibration offset is applied
- Reset calibration to default if needed
Common Issues by Sensor Type
DS18B20 Shows No Data
- Missing pull-up resistor (most common cause)
- Wrong GPIO pin configured in the Configurator
- 1-Wire overlay not enabled in
/boot/config.txt
BME280 Shows No Data
- Wrong I2C address (try 0x76 and 0x77)
- I2C not enabled on the Pi (
sudo raspi-config > Interfacing > I2C)
MH-Z19 Shows No Data
- TX/RX wires crossed incorrectly
- Serial port not enabled (
sudo raspi-config > Interfacing > Serial) - Sensor needs 3-minute warm-up time after power-on
Next Steps
- Deploy Failures if the flow will not deploy
- Device Offline if the Pi is not reachable