Type holding Steinhart-Hart coefficients and extreme values. More...

#include <nrfcxx/sensor/adc.hpp>

Public Member Functions
constexpr	SteinhartHart (float a=1.19438315714902408e-03, float b=2.19852114398042317e-04, float c=1.72427510143621963e-07, uint16_t open_adc16=2281, uint16_t short_adc16=65133)
	Store the coefficients and reference values. More...

int	temperature_cK (unsigned int therm_Ohm) const
	Calculate the temperature corresponding to a measured thermistor resistance. More...

Data Fields
const float	a
	Coefficient of ln(R)^0.

const float	b
	Coefficient of ln(R)^1.

const float	c
	Coefficient of ln(R)^3.

const uint16_t	open_adc16
	16-bit ADC upper threshold for open thermistor. More...

const uint16_t	short_adc16
	16-bit ADC lower threshold for shorted thermistor. More...

Detailed Description

Type holding Steinhart-Hart coefficients and extreme values.

These coefficients are used to calculate the temperature given the measured resistance of an NTC thermistor. Steinhart-Hart is significantly more accurate across a wide range of temperatures than linear interpolation, and generally requires less space than table lookup.

The class also provides calculations for a thermistor installation where Vcc leads to a voltage divider where the top resistor is the thermistor, the bottom resistor is #ref_Ohm, and the ADC is measuring the divided voltage. In this configuration an open thermistor allows no current flow (divided voltage is zero), and a shorted one allows maximum flow (divided voltage is Vcc).

For generality it is assumed a 16-bit ADC is used.

Constructor & Destructor Documentation

◆ SteinhartHart()

constexpr nrfcxx::sensor::adc::SteinhartHart::SteinhartHart	(	float	a = `1.19438315714902408e-03`,
		float	b = `2.19852114398042317e-04`,
		float	c = `1.72427510143621963e-07`,
		uint16_t	open_adc16 = `2281`,
		uint16_t	short_adc16 = `65133`
	)

inlineconstexpr

Store the coefficients and reference values.

Default values correspond to the values for a full-scale (-40 Cel to 200 Cel) measurement with the Adafruit #372 NTC thermistor.

Parameters

a	the coefficient scaling ln(R)^0 in the Steinhart-Hart equation.
b	the coefficient scaling ln(R)^1 in the Steinhart-Hart equation.
c	the coefficient scaling ln(R)^3 in the Steinhart-Hart equation.
open_adc16	the value used to initialize open_adc16.
short_adc16	the value used to initialize short_adc16.
ref_Ohm	the resistance of the top resistor in the measured voltage divider.

Member Function Documentation

◆ temperature_cK()

int nrfcxx::sensor::adc::SteinhartHart::temperature_cK ( unsigned int therm_Ohm ) const

Calculate the temperature corresponding to a measured thermistor resistance.

Parameters

therm_Ohm the measured resistance of the thermistor, in Ohms.

Returns: the estimated temperature of the thermistor in hundredths of a degree Kelvin.

Field Documentation

◆ open_adc16

const uint16_t nrfcxx::sensor::adc::SteinhartHart::open_adc16

16-bit ADC upper threshold for open thermistor.

An open thermistor has an infinite resistance corresponding to an extremely low temperature.

If the measured 16-bit ADC value is at or below this value assume the thermistor is open.

◆ short_adc16

const uint16_t nrfcxx::sensor::adc::SteinhartHart::short_adc16

16-bit ADC lower threshold for shorted thermistor.

A shorted thermistor has a tiny resistance corresponding to an extremely high temperature.

If the measured 16-bit ADC value is at or above this value assume the thermistor is shorted.

The documentation for this class was generated from the following file:

nrfcxx/sensor/adc.hpp

Public Member Functions

Data Fields