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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@tage
The expression will be different for Espruino vs Arduino because analogRead() gives a reading between 0 and 1.
If you have a resistive divider connected to the ADC input and the top resistor is 10k and the NTC resistor is the bottom resistor in the divider, the ADC reading (val) will be R/(10k+R). Where R is the resistance of the NTC. From this simple expression you derive the expression
ohms=10000*val/(1-val),
(ohms in this case is the same as R in the first expression).
so by taking a reading we can calculate the resistance of the NTC resistor. then it is relatively straightforward to use the Steinhart-Hart equation to figure out the temperature.
I don't remember exactly how I got the coefficients, it was something I did about a year ago. I probably found some online calculator. I can look into that tomorrow. The NTC resistor I use has a characteristic as shown in this table
-20 68.915
-15 54.166
-10 42.889
-5 34.196
0 27.445
5 22.165
10 18.010
15 14.720
20 12.099
25 10.000
30 8.309
35 6.939
40 5.824
45 4.911
50 4.160
55 3.539
60 3.024
65 2.593
70 2.233
75 1.929
80 1.673
You could try this online calculator, and plug in three values from the table.
http://www.thinksrs.com/downloads/programs/Therm%20Calc/NTCCalibrator/NTCcalculator.htm