| Sensor | Range | Typical accuracy | Interface | Indicative price |
|---|---|---|---|---|
| DS18B20 (waterproof probe) | −55 to 125 °C | ±0.5 °C from −10 to 85 °C | 1-Wire | ₹80–160 |
| DHT22 | −40 to 80 °C | ±0.5 °C (+ humidity) | Single-wire | ₹180–320 |
| SHT31 | −40 to 125 °C | ±0.3 °C (+ humidity) | I2C | ₹300–600 |
| BME280 | −40 to 85 °C | ±1 °C (+ humidity, pressure) | I2C / SPI | ₹350–650 |
| LM35 | 2 to 150 °C in the basic circuit | ±0.5 °C at 25 °C | Analog, 10 mV per °C | ₹60–120 |
| NTC 10 k thermistor | Roughly −40 to 125 °C (varies by part) | About ±1 °C after calibration | Analog (divider) | ₹10–60 |
| MAX6675 + K-type thermocouple | 0 to 1,024 °C | A few °C | SPI | ₹250–450 |
| MLX90614 (non-contact) | −70 to 380 °C (object) | ±0.5 °C near room temperature | I2C | ₹600–1,200 |
“Best” depends on what you’re measuring: room air, water, soil, a hot oven or a surface you can’t touch. Ranges and accuracy are typical datasheet values (Maxim/Analog Devices, Aosong, Sensirion, Bosch, TI, Melexis); prices are indicative for Indian modules.
For water, soil, fridges and outdoors: DS18B20
A sealed stainless-steel probe on a cable — drop it in a tank, bury it in soil or tape it inside a cold room. Digital, accurate, and many probes share one data pin. Needs a 4.7 kΩ pull-up. Reads −127 °C? That’s a wiring fault — fix.
Guides: DS18B20 with ESP32, with Uno. Project: cold storage alert.
For rooms (with humidity): DHT22, SHT31 or BME280
- DHT22 — cheapest that’s good enough.
- SHT31 — most accurate and fast; best for incubators and logging.
- BME280 — adds pressure for weather stations.
Full comparison: DHT22 vs BME280 vs SHT31. Avoid the DHT11 for anything above 50 °C — DHT11 vs DHT22.
For learning analog: LM35
Pinout, wiring and errors: LM35 component page.
Outputs 10 mV per °C — 30 °C reads as 0.30 V. Great for understanding analogRead() on an Uno.
- Needs at least 4 V supply, so power it from 5 V even on an ESP32; its output stays well under 3.3 V for normal temperatures.
- Long wires pick up noise; keep them short or average many readings.
Cheapest: NTC thermistor
A resistor whose value falls as it warms. Pennies each, used inside battery packs and appliances. Needs a fixed resistor as a divider and the B-value maths (or a lookup table) to convert to °C. Accuracy depends on your calibration.
Hot things: MAX6675 + K-type thermocouple
Ovens, kilns, tandoors, soldering stations, motor housings — up to about 1,000 °C. The thermocouple probe survives heat; the MAX6675 board stays cool and talks SPI.
Without touching: MLX90614
An infrared thermometer that reads a surface’s temperature from a short distance. Good for motor or bearing temperature, cooking surfaces, or a contactless thermometer. It measures the average over a cone that widens with distance, so get close to small targets. Shiny metal reads wrong — put a strip of matte tape on it.
Component: MLX90614.
Verdict
| Measuring | Pick |
|---|---|
| Water, soil, cold room, outdoors | DS18B20 probe |
| Room temperature + humidity | DHT22 (budget) or SHT31 (accuracy) |
| Weather station | BME280 |
| Learning analog on an Uno | LM35 |
| Ovens, kilns, very hot | MAX6675 + K-type |
| Surfaces, without contact | MLX90614 |