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The ADC reading was determined using NTC thermistors (unlike MSX, which used thermocouples), and then put through an equation in order to determine the temperature.

Equations

Steinhart–Hart equation

The Steinhart-Hart equation models the resistance of a semiconductor at various temperatures. You can read up on the equation online, but this is the equation of interest (which was taken from the NTCLE100E3 datasheet).

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where 

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body R_{25}

is the reference resistance of the thermistor taken at room temperature (25 °C)

Voltage-Divider equation

A voltage-divider is a circuit which turns a large voltage into a smaller one, using two resistors in series and an input voltage. This equation states that the output voltage is directly proportional to the input voltage and the ratio of

Mathinline
body R

 and 

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body R_{ref}

, where 

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body R_{ref}

 is the fixed resistor, and 

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body R_{cc}

 is the power supply voltage.

ADC equation

An ADC reports a ratio between

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body 0V

and the supply voltage, using however many bits of resolution.

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body \text{ADC reading} = \frac{V_o (2 ^ \text{bits of resolution} - 1)}{V_{cc}}

, where 

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body V_o

 is the system voltage, 

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body V_{cc}

 is the voltage measured, and 

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body \text{ADC reading}

 is the value read back from the ADC.

Derivation

The goal is to determine Temperature (T) as a function of the ADC-reading.

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