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Latest Version: 2.0.0

This library makes it simple for an imp to read an NTC (“Negative Temperature Coefficient”) thermistor and determine the temperature. Thermistors are essentially temperature-dependent resistors. To use as a thermometer, a thermistor is used as half of a resistive divider, where the voltage across the full divider is known. The imp then reads the voltage at the center of the divider to determine the ratio of resistance of the thermistor and the bias resistor (also the nominal resistance of the thermistor), from which the temperature can be derived.

You can view the library’s source code on GitHub. Click here to see information on other versions of this library.

To add this library to your project, add #require "Thermistor.class.nut:2.0.0" to the top of your device code


A resistive divider can be formed with the thermistor on the top or the bottom; this class allows for either configuration. The top of the divider should be connected to the same rail as an imp’s VDDA pin (or VDD pin, in the case of the imp001, as VDD and VDDA are internally connected). The bottom of the divider should be connected to ground.

The resistance of the bias resistor in the voltage divider should be equal to the nominal resistance of the thermistor (the resistance at T0). This simplifies the temperature calculation and allows the largest dynamic range.

The center of the divider must be connected to a pin capable of analog input. On the imp001, any pin can be used as an analog input. On the imp002, imp003 and imp004m, only some pins can be configured this way, so check the appropriate Imp Pin Mux chart. The imp005 does not support analog input.

Class Usage

Constructor: Thermistor(pin, b_therm, t0_therm[, points][, high_side_therm])

The thermistor class takes three to five parameters. Three are required, two are optional:

Parameter Name Description Optional/Required
pin Imp pin object capable of analog input Required
b_therm Thermistor ß parameter, from datasheet Required
t0_therm Thermistor T0 parameter, from datasheet Required
points Number of readings to average when reading the thermistor Optional, defaults to 10
high_side_therm Set false to place thermistor on low side of divider Optional, defaults to true

The ß and T0 parameters are all available on the thermistor datasheet:

Parameter Meaning
ß Characteristic of the thermistor. Most thermistors have many ß values listed, for various temperature ranges. Choose the value for the temperature range you will be operating in.
T0 Temperature at which the nominal resistance (R) of the thermistor is measured. Typically room temperature (~25°C)
#require "Thermistor.class.nut:2.0.0"

const b_therm = 3988;
const t0_therm = 298.15;
pin <- hardware.pin9;

// Thermistor on bottom of divider
myThermistor <- Thermistor(pin, b_therm, t0_therm, 10, false);

Class Methods


The read() method returns the temperature in Celsius.

local celsius =;


The read() method returns the temperature in Kelvin.

local kelvin = therm.readK();

Release History

The Electric Imp Dev Center documents the latest version of the library. For past versions, please see the Electric Imp public GitHub repos listed below.

Version Source Code Notes
1.0.0 GitHub Initial release
2.0.0 GitHub readF() method removed and readC() renamed for consistency with other libraries


Thermistor is licensed under MIT License.