Best Sensors for IoT Projects

Best Sensors for IoT Projects

There are hundreds of sensors available for microcontroller projects, but a small set covers the vast majority of real-world use cases. This guide covers the sensors worth knowing — with actual specs, the protocol they use, typical price in India, and what projects they are suited for.

Temperature and Humidity

DHT22 (AM2302)

Range: -40 to +80°C (±0.5°C accuracy), 0–100% RH (±2–5% accuracy). Single-wire protocol. Minimum 2-second interval between readings. Needs a 10 kΩ pull-up resistor on the data line. Price: ₹130–180.

The DHT22 is the go-to for most indoor/outdoor temperature monitoring. Use it for weather stations, greenhouse monitoring, HVAC control, and cold chain logging.

DHT11

Range: 0–50°C (±2°C), 20–90% RH (±5%). Cheaper at ₹50–80 but less accurate and limited to positive temperatures. Fine for classroom demos; use DHT22 for anything you actually deploy.

BME280

Measures temperature (±1°C), humidity, and barometric pressure (300–1100 hPa). I2C or SPI interface. Ultra-compact — fits on a 2.5 × 2.5 mm package. Price: ₹180–250 for the module. Better than DHT22 for weather stations because of the pressure sensor. Use for altitude estimation, weather prediction, and HVAC systems.

Gas and Air Quality

MQ-135

Detects NH₃, NOₓ, alcohol, benzene, smoke, CO₂. Analog output. Requires warm-up time (24–48 hours for initial burn-in, 20 seconds before each reading). Output is a resistance ratio — needs calibration against known gas concentrations for accurate ppm values. Price: ₹60–100. Good for relative air quality index, not precise ppm measurement.

MQ-2

Sensitive to LPG, propane, hydrogen, methane, smoke. Use for kitchen gas leak detection and smoke alarms. Same analog output approach as MQ-135. Price: ₹60–90.

MQ-7

Specifically calibrated for carbon monoxide (CO). Requires voltage cycling (5V for 60s, then 1.4V for 90s) for accurate readings — more complex to implement properly. Price: ₹70–110.

Distance and Proximity

HC-SR04 Ultrasonic Sensor

Range: 2–400 cm, accuracy ±3 mm, 5V supply, Trig and Echo digital pins. Uses 40 kHz ultrasonic pulses and measures time-of-flight. Price: ₹40–70.

The workhorse for distance measurement, water level detection, obstacle avoidance, and smart parking. Note: ESP32 operates at 3.3V logic — use a voltage divider on the Echo pin (5V output → 3.3V input) to protect the GPIO.

VL53L0X (ToF Sensor)

Time-of-flight laser ranging sensor, I2C interface, 30–1200 mm range, 1 mm resolution, works regardless of target color or reflectivity (unlike ultrasonic). Price: ₹200–300. Better than HC-SR04 for short-range precision applications and robotics.

Sharp IR Distance Sensors (GP2Y0A21)

Analog output, 10–80 cm range, reliable in low-light but affected by surface color and angle. Price: ₹200–350. Good for robotics line-of-sight obstacle detection.

Motion and Presence

HC-SR501 PIR Sensor

Passive infrared, detects human body heat movement, 5V supply, digital output. Adjustable sensitivity (3–7 m) and time-delay (3 seconds to 5 minutes) via two potentiometers. Price: ₹40–70. The standard for motion-activated lighting, security systems, and occupancy detection.

Soil and Moisture

Capacitive Soil Moisture Sensor v1.2

Analog output (0–3.3V), measures dielectric permittivity of soil without metal probes touching the soil. Does not corrode like resistive sensors. Price: ₹80–150. The right choice for long-term smart irrigation deployments. Calibrate by recording ADC value in dry air and submerged in water.

Current and Power

ACS712 Current Sensor

Hall-effect based, available in ±5A, ±20A, ±30A variants. Analog output proportional to current. Supply voltage: 5V. Sensitivity: 185 mV/A (5A version), 100 mV/A (20A). Price: ₹80–130.

Use for energy monitoring, overcurrent detection, and motor current sensing. The ACS712 is not precision — use an INA219 (I2C, 0.1% accuracy) if you need accurate power measurement.

Sensor Protocol Quick Reference

• Digital single-wire: DHT11, DHT22, DS18B20 (temperature probe)
• I2C: BME280, BMP280, MPU-6050, VL53L0X, OLED displays, INA219
• SPI: RC522 RFID, SD card, MAX6675 thermocouple
• UART: GPS (NEO-6M), SIM800L GSM, fingerprint scanner
• Analog: MQ-series gas sensors, soil moisture, LDR, NTC thermistor

For your next project build, browse sensors at Circuitkar — all modules tested and ready to use with Arduino and ESP32.