Arduino and Temperature Measurement: Thermistor Calculations and Circuit Design

Temperature measurement is a common application in electronics projects, often achieved using thermistors with Arduino microcontrollers. Understanding how to calculate resistance changes and design circuits is essential for accurate readings.

Thermistors and Their Types

Thermistors are temperature-sensitive resistors that change resistance with temperature. There are two main types:

• NTC (Negative Temperature Coefficient): Resistance decreases as temperature increases.
• PTC (Positive Temperature Coefficient): Resistance increases as temperature increases.

Calculating Resistance and Temperature

The resistance of a thermistor at a specific temperature can be calculated using the Steinhart-Hart equation or a simplified Beta parameter equation. The Beta equation is commonly used:

R_T = R₀ * exp(B * (1/T – 1/T₀))

Where:

• R_T: Resistance at temperature T
• R₀: Resistance at reference temperature T₀
• B: Beta coefficient (provided by thermistor datasheet)
• T: Temperature in Kelvin
• T₀: Reference temperature in Kelvin

Circuit Design for Temperature Measurement

A common circuit involves connecting the thermistor in a voltage divider configuration with a known resistor. The voltage across the thermistor is read by the Arduino analog input to determine temperature.

Key steps include:

• Selecting an appropriate resistor value based on thermistor resistance.
• Connecting the thermistor and resistor in series between V_cc and ground.
• Measuring the voltage at the junction point with Arduino analog pin.

The voltage reading can then be converted to resistance and temperature using the formulas provided.