Liasis

Arduino library for the NorthernWidget longwave pyrgeometer

Liasis is a genus of Australian water and olive pythons. Like all pythons, they possess labial pit organs — heat-sensing cavities along the lips that detect thermal infrared radiation in the ~5–30 µm range, the same window in which warm objects near ambient temperature emit most strongly. It is the same physical phenomenon this library measures.

This library interfaces with the NorthernWidget longwave pyrgeometer module, which measures atmospheric downwelling thermal infrared radiation via a ZTP-135SR thermopile, along with housing temperature for reference compensation.

The shortwave (solar) sensor that was formerly bundled with this library's predecessor is maintained separately as Libelle — named after the German word for dragonfly, whose compound eyes span UV to near-infrared.

Channels

Column (getHeader())	Method	Description
IR_Long [mV]	getThermo()	Thermopile raw output voltage (mV)
IR_Long [C]	getThermoC()	Longwave-derived temperature (°C)
PyrgT [C]	getTemp()	Housing temperature from thermistor (°C)

The thermopile measures the net radiation exchange between the sensor and the sky above, which is dominated by atmospheric thermal emission in the 8–14 µm window. Housing temperature is required for reference junction compensation to obtain calibrated irradiance.

Hardware

The longwave module reads the ZTP-135SR thermopile and its integrated thermistor through a Texas Instruments ADS1115 16-bit ADC at I2C address 0x4A. Signal conditioning is handled by a pair of LTC2054 zero-drift op-amps.

Key ICs: Amphenol ZTP-135SR (thermopile + thermistor), ADS1115 (ADC), LTC2054 (op-amp)

Basic usage

#include <Liasis.h>

Liasis pyrgeo;

void setup() {
    Serial.begin(9600);
    if (!pyrgeo.begin()) {
        Serial.println("Liasis not found. Check wiring.");
        while (1);
    }
    Serial.println(pyrgeo.getHeader());
}

void loop() {
    Serial.println(pyrgeo.getString());
    delay(1000);
}

API

Method	Returns	Description
begin()	bool	Initialize sensor and I2C bus; returns false if ADS1115 not found
getHeader()	String	Comma-separated column names with units
getString()	String	Comma-separated measurement values
getThermo()	float	Thermopile raw output voltage (mV)
getThermoC(accuracy)	float	Longwave-derived temperature (°C); accuracy 0 = low (default), 1 = high
getTemp()	float	Housing temperature from thermistor (°C)

Name history

This library was split from the combined Monarch library (formerly Dyson), which housed both the shortwave and longwave sensors in a single codebase. On the split, the longwave sensor became Liasis and the shortwave sensor became Libelle. The combined archive is preserved at NorthernWidget-Skunkworks/Monarch-Dyson_Library__Archive.

Liasis continues the NorthernWidget tradition of naming instruments after organisms with exceptional sensory capabilities.

The hardware project lives at NorthernWidget-Skunkworks/Project-Monarch.

License

GNU General Public License v3

Full API reference: https://docs.northernwidget.com/Liasis_Library/