Thermistor voltage divider

Predict how a falling thermistor resistance changes a divider voltage.

Physics Phoebe, your practice guide

Physics Phoebe
Predict the reading, then compare it with the measurement.

Falstad CircuitJS

Third party Tool

Predict how a falling thermistor resistance changes a divider voltage.

Tier 1 · Web · No account

Version tested: Browser tool opened 2026-09-05; no version number exposed. Date: 2026-09-05.

Open the prepared circuit.

Open this circuit in Falstad (new tab)

Steps

Screens captured against Falstad CircuitJS Browser tool opened 2026-09-05; no version number exposed on 2026-09-05; the tool may have moved on — the text steps are the contract.

  1. Step 1

    Do
    In the circuit canvas, inspect the 5 V source and the two 10 kΩ resistors.
    You will see
    The 10 kΩ fixed resistor sits above the 10 kΩ thermistor model in the running circuit.
    Why it matters
    The chapter uses a voltage divider to turn resistance into voltage. The fixed resistor and sensor share the supply according to their resistance values.

  2. Step 2

    Do
    In the circuit canvas, point at the wire leaving the midpoint and read its measurement panel.
    You will see
    The midpoint measurement panel shows 2.5 V.
    Why it matters
    The midpoint is the voltage an ADC would sample. The chapter separates this raw voltage from the digital count and final physical reading.

  3. Step 3

    Do
    In the circuit canvas, use the resistor labels to calculate 5 × 10000 / (10000 + 10000).
    You will see
    Both labels show 10 kΩ, and the calculation gives 2.5 V, matching the midpoint reading.
    Why it matters
    Equal resistances divide the supply equally. This checks the divider calculation before you ask it to explain a changed sensor resistance.

  4. Step 4

    Do
    In the lower resistor’s right-click menu, choose Edit and set Resistance to 5000 Ω.
    You will see
    The lower resistor label changes to 5 kΩ, and the midpoint measurement falls to 1.667 V.
    Why it matters
    The lower resistance models a warmer NTC. The ADC sees the resulting voltage change, so temperature still needs a conversion from the sensor response.

  5. Step 5

    Do
    In the lower resistor’s right-click menu, choose Edit and set Resistance to 20000 Ω.
    You will see
    The lower resistor label changes to 20 kΩ, and the midpoint measurement rises to 3.333 V.
    Why it matters
    The colder model moves the midpoint in the opposite direction. The chapter’s sensitivity discussion explains why resistance and voltage changes are not simply proportional.

  6. Step 6

    Do
    In the lower resistor’s right-click menu, choose Edit and restore Resistance to 10000 Ω.
    You will see
    The lower resistor returns to 10 kΩ, and the midpoint measurement returns to 2.5 V.
    Why it matters
    Returning to balance checks the starting result again. It does not test ADC loading, where the input circuit changes the voltage it measures.

Chapter checks

These questions refer to the chapter’s examples. Use the return links to review their answers.

  1. Why does a resistive sensor such as a thermistor or LDR usually need a voltage-divider circuit before it can be read by a microcontroller?

    Return to the chapter’s knowledge check

  2. A divider uses a fixed top resistor and a sensor bottom resistor, fed from the same 3.3 V rail that supplies the ADC reference. The 3.3 V rail sags to 3.1 V under load. What happens to the ADC code for a fixed sensor resistance?

    Return to the chapter’s knowledge check

Return to Resistive Dividers and ADC Loading · Browse Labs