Telemetry Channels¶

The Inhero MR2 transmits telemetry data in CayenneLPP format across four channels. The MeshCore app displays these as Channel 1–4.

Channel 1 — Device Status¶

Base data from the node.

Field	Unit	Source	Description
Battery Level	% / V	INA228	See note below on SOC workaround
Temperature	°C / °F	nRF52840	MCU die temperature

Battery Level & SOC Workaround¶

MeshCore currently transmits only battery voltage on Channel 1 — there is no native SOC% field. The MeshCore app converts this voltage back to a percentage using a hardcoded Li-ion discharge curve. This works well for Li-ion cells but produces wrong readings for LiFePO₄, LTO, or Na-ion chemistries (which have a much flatter voltage curve).

The MR2 works around this limitation:

SOC State	What `getBattMilliVolts()` returns	App displays
SOC not yet valid	Real battery voltage from INA228	Percentage based on Li-ion curve (may be inaccurate for non-Li-ion)
SOC valid (coulomb counter calibrated)	Fake Li-ion OCV reverse-mapped from true SOC% (`socToLiIonMilliVolts()`)	Correct percentage — the app's Li-ion curve decodes back to the original SOC%

OCV = Open Circuit Voltage — the battery's resting voltage without load. The OCV curve (voltage vs. SOC%) is characteristic for each battery chemistry and is used here as a lookup table to reverse-map SOC% back to a voltage the app can interpret.

The SOC becomes valid as soon as a reference point exists — either manually via set board.soc <percent> or automatically on a "Charging Done" event (which sets SOC to 100%).

Without set board.batcap <mAh> a chemistry-typical default capacity (1500–2000 mAh) is assumed. Setting the real capacity is therefore required for the displayed percentage and the Batt-TTL to be accurate — not for the SOC to become valid.

The reverse mapping uses a piecewise-linear Li-ion OCV table (3000 mV at 0% → 4200 mV at 100%). This ensures the app displays the correct coulomb-counted SOC regardless of the actual battery chemistry.

Channel 2 — Environment (BME280)¶

Data from the BME280 environment sensor (always present on the MR2).

Field	Unit	Source	Description
Temperature	°C / °F	BME280	Ambient temperature
Relative Humidity	%	BME280	Relative humidity
Barometric Pressure	hPa	BME280	Barometric pressure
Altitude	m / ft	BME280	Altitude derived from barometric pressure (reference: sea level)

Note: The altitude calculation is based on standard sea level pressure (1013.25 hPa) and may deviate depending on weather conditions.

Channel 3 — Battery (INA228 / BQ25798)¶

High-precision battery data from the INA228 coulomb counter and BQ25798 charge controller.

Field	LPP Type	Unit	Source	Description
Voltage	Voltage	V	INA228	Battery voltage (20-bit ADC, ±0.1% accuracy)
SOC	Percentage	%	INA228	State of charge via coulomb counting — optional, only when calibrated
Current	Current	A	INA228	Battery current. Negative = discharging, positive = charging
Temperature	Temperature	°C / °F	BQ25798 NTC	Battery temperature from NTC thermistor
Batt-TTL	Distance	days	calculated	Estimated time-to-live (remaining runtime) — optional, only with valid SOC

SOC & Batt-TTL¶

SOC and Batt-TTL only appear when the coulomb counter has a valid reference point — either a manual SOC set (set board.soc) or a "Charging Done" event. The percentage is based on the configured battery capacity (set board.batcap; a chemistry-typical default of 1500–2000 mAh is assumed otherwise). Until the SOC is valid, these fields are omitted.

Batt-TTL Encoding¶

The Batt-TTL is transmitted as a CayenneLPP Distance value in days, since CayenneLPP has no native "duration" type. The MeshCore app displays it as a distance (e.g. "42 m"), but the value represents days of remaining runtime.

Condition	Transmitted Value	Meaning
Finite Batt-TTL	`ttlHours / 24.0`	Estimated remaining days on battery
Surplus (charging > consumption)	`990.0` (sentinel value)	Effectively infinite — device is gaining charge
Unknown (SOC not yet valid)	not sent	Batt-TTL cannot be calculated yet

Temperature Sentinel Values¶

Invalid temperature readings are indicated by sentinel values and not transmitted to the app:

Value	Meaning
−999 °C	I²C communication error
−888 °C	ADC not ready
−99 °C	NTC open (not connected)
+99 °C	NTC shorted

Channel 4 — Solar (BQ25798)¶

Solar input data from the BQ25798 charge controller.

Field	LPP Type	Unit	Source	Description
Voltage	Voltage	V	BQ25798	Solar input voltage (VBUS)
Current	Current	A	BQ25798	Solar input current (IBUS)
MPPT 7-Day	Percentage	%	Firmware	MPPT activation over the last 7 days. Shows what percentage of time the MPPT regulator was actively harvesting solar energy.

Note — Solar current accuracy: The BQ25798 IBUS ADC has a resolution of 1 mA (15-bit mode) but exhibits significant measurement error at low currents (~±30 mA). Values below approximately 150 mA should be treated as rough estimates. For precise current measurement, the battery side uses the INA228 instead.

Note: The MPPT percentage is a rolling 7-day average. A low value (e.g. 1%) means the panel rarely delivers enough power to activate the MPPT regulator — e.g. during overcast conditions or suboptimal panel angle.

Channel Assignment in Code¶

Channels are assigned dynamically:

Channel 1 (TELEM_CHANNEL_SELF) is statically defined and contains the MeshCore base data (battery voltage and MCU die temperature).
querySensors() assigns each active sensor its own channel starting right after Channel 1 — the BME280 therefore lands on Channel 2.
The battery channel is determined by queryBoardTelemetry() as the next free channel (findNextFreeLppChannel).
The solar channel = battery channel + 1.

querySensors() assigns the BME280 to Channel 2 before queryBoardTelemetry() runs, so battery data lands on Channel 3 and solar on Channel 4 in practice.

Order in CayenneLPP packet:
┌───────────────────────────────────────────────┐
│ Channel 1: Voltage (INA228 / SOC fake)        │  ← MyMesh.cpp (getBattMilliVolts)
│ Channel 2: Temp, Humidity, Pressure, Alt.     │  ← BME280 (querySensors)
│ Channel 3: VBAT, [SOC], IBAT, TBAT, [Batt-TTL]     │  ← queryBoardTelemetry()
│ Channel 4: VSOL, ISOL, MPPT%                  │  ← queryBoardTelemetry()
│ Channel 1: MCU die temperature                │  ← MyMesh.cpp (getMCUTemperature)
└───────────────────────────────────────────────┘

Permissions: Channels 2–4 are only sent if the requesting client has the TELEM_PERM_ENVIRONMENT permission. Guests (Guest role) receive only Channel 1 with base voltage and MCU temperature.