Use a negative temperature coefficient temperature sensor with a simple voltage divider to obtain stable temperature readings in electronic control systems. Connect the sensing resistor in series with a fixed resistor between a regulated supply and ground, then measure the midpoint voltage with an analog input. A common configuration uses a 10 kΩ temperature sensor at 25 °C paired with a 10 kΩ reference resistor and a 3.3 V or 5 V supply.
The sensing element decreases resistance as temperature rises. For example, a typical 10 kΩ device measures about 10 kΩ at 25 °C, ~6.5 kΩ at 35 °C, and ~3.6 kΩ near 50 °C. This predictable change allows the midpoint voltage in the divider network to shift proportionally. When connected to an ADC pin of a microcontroller, the measured voltage can be converted to temperature through a lookup table or the Beta parameter equation.
For stable measurements, place the sensing component close to the monitored surface and keep the analog trace short. Add a small 0.01–0.1 µF capacitor from the measurement node to ground to reduce noise. Choose the fixed resistor value close to the sensor resistance at the expected mid-range temperature; this improves voltage resolution across the working range.
Designers often integrate this temperature-dependent resistor into power supply protection, battery packs, fan controllers, and embedded monitoring units. The divider layout, resistor matching, and ADC reference voltage determine measurement accuracy, so each element of the electrical layout should be selected with the expected temperature span in mind.
NTC Thermistor Circuit Diagram With Voltage Divider Wiring and Temperature Sensing
Place the temperature-dependent resistor in series with a fixed resistor between the supply rail and ground, and connect the midpoint to an analog measurement pin. With a 3.3 V supply and a 10 kΩ sensing element rated at 25 °C, pair it with a 10 kΩ reference resistor. This arrangement produces a midpoint voltage near 1.65 V at room temperature, allowing balanced measurement resolution across moderate temperature ranges.
The midpoint voltage depends on the resistance ratio inside the divider network. When the sensing element heats up, its resistance drops, shifting the node voltage. For example, with a 5 V supply and a 10 kΩ reference resistor:
- 10 kΩ sensor → ~2.5 V output
- 5 kΩ sensor → ~1.67 V output
- 2.5 kΩ sensor → ~1.0 V output
Choose the reference resistor according to the expected temperature span. Matching its value to the sensor resistance near the midpoint of the working temperature range spreads the voltage change more evenly across the analog input range.
Common resistor pair selections include:
- 10 kΩ sensor + 10 kΩ reference for 0–50 °C monitoring
- 10 kΩ sensor + 6.8 kΩ reference for 20–80 °C systems
- 10 kΩ sensor + 4.7 kΩ reference for higher temperature measurement
Stabilize the measurement node with a small capacitor connected to ground. Values between 10 nF and 100 nF reduce high-frequency noise from switching regulators or long PCB traces. The capacitor and divider resistance form a low-pass filter that smooths ADC readings.
Convert the measured voltage into temperature using resistance calculation followed by the Beta equation. Many embedded controllers use a lookup table containing resistance values at fixed temperature steps such as 0 °C, 10 °C, 25 °C, 50 °C, and 80 °C. Interpolating between these points yields accurate temperature readings across the full measurement range.
How an NTC Thermistor Works in a Voltage Divider Temperature Measurement Circuit
Connect the temperature-dependent resistor and a fixed resistor in series between the supply line and ground, then read the midpoint voltage with an analog input. A common setup uses a 10 kΩ sensor at 25 °C with a 10 kΩ reference resistor powered from 3.3 V or 5 V. The measured node voltage shifts as the sensing element changes resistance with temperature.
Resistance change and voltage behavior
The sensing element shows decreasing resistance as temperature rises. For a device with Beta ≈3950:
0 °C → ~32 kΩ
25 °C → 10 kΩ
50 °C → ~3.6 kΩ
75 °C → ~1.8 kΩ
Placed in a divider network, this resistance drop pulls the midpoint voltage downward if the sensor is connected toward ground. The analog input therefore receives a predictable voltage shift tied to temperature.
Voltage calculation example
The midpoint voltage follows the relation:
Vout = Vcc × (R_sensor / (R_sensor + R_fixed))
With a 5 V supply and a 10 kΩ reference resistor:
25 °C → 2.5 V
50 °C → ~1.3 V
75 °C → ~0.75 V
Microcontrollers convert this voltage using an ADC. A 10-bit converter with a 3.3 V reference produces 1024 steps, giving about 3.22 mV per step. That resolution typically yields temperature precision between 0.2 °C and 0.5 °C across moderate ranges when the resistor pair is matched to the measurement span.
Accuracy improves by keeping the sensing element close to the monitored surface, using a stable reference resistor with 1 % tolerance, and adding a 10–100 nF capacitor from the measurement node to ground to smooth electrical noise before the ADC input.