Serial Output

Every Sensor Net node outputs diagnostic and data messages over USB serial at 115200 baud. The receiver node’s serial output is particularly important because it is the data that the monitor application reads. This page explains how to read the output from each node type.

Opening the Serial Monitor

Using PlatformIO:

pio device monitor

Or with any serial terminal application, connect to the board’s port at 115200 baud. On macOS the port looks like /dev/tty.usbmodemXXXX. On Windows it appears as COM3 or similar.

Receiver Node Output

When the receiver boots, it prints a header:

=== LoRa Receiver Node AABBCCDD ===
Firmware 2.0.0  |  Mesh max-hops=3

[RADIO] SX1262 ready

Once sensor nodes are transmitting, the receiver prints one [REPORT] line per received packet:

[REPORT] node=11223344 type=temperature value=23.45 unit=C rssi=-45 snr=8.5 uptime=120 tx=15 hops=0
[REPORT] node=55667788 type=pressure value=1013.25 unit=hPa rssi=-62 snr=5.2 uptime=300 tx=60 hops=1

Report Fields

Each [REPORT] line contains these key=value pairs:

Field	Type	Description
node	Hex string	Unique ID of the originating sensor node (from its MAC address)
type	String	Sensor type: temperature or pressure
value	Float	The sensor reading
unit	String	Unit of measurement: C (Celsius) or hPa (hectopascals)
rssi	Integer	Received Signal Strength Indicator in dBm (closer to 0 = stronger)
snr	Float	Signal-to-Noise Ratio in dB (higher = cleaner signal)
uptime	Integer	Seconds since the originating node last booted
tx	Integer	Total number of reports the originating node has sent
hops	Integer	Number of mesh relay hops (0 = received directly)

This format is intentionally machine-readable. The monitor application uses a regex parser to extract these fields from each line. See the Serial Packet Format Reference for the exact specification.

Sensor Node Output

Temperature and pressure nodes print similar output:

=== LoRa Temperature Node AABBCCDD ===
[RADIO] SX1262 ready
[SENSOR] TMP102 ready
[TX] TMP102=23.45 C  #1 (22 bytes)
[TX] TMP102=23.50 C  #2 (22 bytes)
[RELAY] 55667788 hop 1 (26 bytes)

Prefix	Meaning
[RADIO]	Radio initialization status
[SENSOR]	Sensor initialization status
[TX]	The node just transmitted its own sensor reading. Shows sensor name, value, unit, sequence number, and packet size in bytes.
[RELAY]	The node relayed another node’s packet. Shows the originating node ID, the hop count of the relayed packet, and packet size.

Understanding RSSI and SNR

Two fields in the receiver output are especially useful for diagnosing network issues:

RSSI (Received Signal Strength Indicator) is measured in dBm. It tells you how strong the received radio signal was.

RSSI Range	Signal Quality
-30 to -60 dBm	Excellent (very close range)
-60 to -90 dBm	Good
-90 to -110 dBm	Fair
-110 to -120 dBm	Weak (edge of usable range)
Below -120 dBm	At or below the noise floor

SNR (Signal-to-Noise Ratio) is measured in dB. It tells you how far the signal is above the background noise.

SNR Range	Signal Quality
Above 5 dB	Excellent
0 to 5 dB	Good
-5 to 0 dB	Marginal (LoRa can still decode)
Below -5 dB	Poor (likely packet loss)

LoRa is unique in that it can successfully decode signals with negative SNR — meaning the signal is actually below the noise floor. This is a property of the chirp spread spectrum modulation.

Using the Hop Count

The hops field tells you how the packet reached the receiver:

• hops=0 — The receiver heard the packet directly from the originating sensor node.
• hops=1 — The packet was relayed once by an intermediate node.
• hops=2 — The packet was relayed twice.

If all packets arrive with hops=0, your nodes are all within direct radio range of the receiver. If you see hops=1 or higher, the mesh relay system is actively forwarding packets through intermediate nodes.

Next Step

To learn how to modify the firmware and add new sensor types, see Extending the Firmware.