Temperature Sensing (NTC divider)

Turns temperature into a voltage an ADC can read — with a sensor that costs two cents. This is how the vast majority of products measure temperature: battery packs, 3D printer hotends, coffee machines.

TH1 — the NTC thermistor. A resistor that loses resistance as it warms (Negative Temperature Coefficient) — 10 kΩ at 25 °C, roughly halving every ~20 °C. That curve is steep and predictable, which is why a two-cent part beats many "real" sensor ICs on sensitivity.
R1 — the fixed half of the divider. Out = VCC · R1/(R1 + TH1), with the NTC on top: as it warms, its resistance shrinks and the output rises — the intuitive direction. R1 is chosen equal to the NTC's 25 °C value so room temperature sits at mid-rail — right where the divider's slope (and your resolution) is best.
C1 — gives the ADC's sampling capacitor a stiff source and quietly averages the noise a long sensor wire picks up.

Converting the reading: resistance → temperature uses the B equation (B = 3950 here) or, for real accuracy, the Steinhart–Hart fit. Every firmware ecosystem has a lookup-table generator for exactly this divider.

Exposes: vcc (use the ADC's reference rail — see the ratiometric note), out (to an ADC pin), gnd.

⚠ The sensor heats itself with its own measuring current, then dutifully reports its own warmth. Keep divider current well under a milliamp — the limits note has the numbers.

Inside this block

TH1

10k B3950

the sensor, on top — resistance falls as temperature rises (Negative Temperature Coefficient), so the output RISES as it warms: the intuitive direction

10k 1%

the fixed half of the divider, on the bottom — matched to the NTC's 25 °C resistance so the output sits at mid-rail at room temperature, where sensitivity is best

100n

filter — gives the ADC's sample capacitor a low-impedance source and averages out noise picked up on the sensor wiring

Limits & gotchas

⚠selfheat.note 0 — Current through the NTC heats it — and it measures its own heat as 'temperature'. At 3.3 V / 20 kΩ total that's ~0.5 mW: fine. Use a 1k NTC on 5 V and self-heating reads degrees high. Bigger divider = truer reading (the filter cap keeps the ADC happy anyway).

⚠ratiometric.note 0 — Power this divider from the ADC's OWN reference rail. Then VCC wobble cancels out of the ratio and the reading doesn't care — that's a ratiometric measurement, and it's free if you wire it right.

Use this block in a real design

Drop it on a canvas, wire it up, and watch the live checks — free, no card.

Start designing →

✦This page is generated from the block's source — the same content powers the editor's explanations and live checks.