Pinout

HC-SR04 ultrasonic distance sensor (4-pin) pinout

Pins

Supply voltage	5 V DC
Working current	15 mA
Logic level	5 V (TRIG and ECHO)
Measuring range	2–400 cm
Resolution	≈3 mm
Measuring angle	15°
Ultrasonic frequency	40 kHz
Trigger pulse	10 µs HIGH
Distance formula	Echo time (µs) / 58 = cm
Measurement cycle	≥ 60 ms between pings recommended
Size	45 × 20 × 15 mm

ECHO is a 5V output. Feeding it straight into a 3.3V MCU input (ESP32, most ARM boards) is out of spec — use a voltage divider (e.g. 1kΩ over 2kΩ) or a level shifter first.
~15° detection cone, 2–400 cm range; soft or angled surfaces absorb or deflect the ping instead of returning it.

DHT11 / DHT22 temperature & humidity sensor (4-pin)Supply voltage: DHT11: 3–5.5 V; DHT22: 3.3–6 V; Interface: Single-wire digital (proprietary, not 1-Wire); Pull-up on DATA: 4.7–10 kΩ to VCC
PIR motion sensor (HC-SR501, 3-pin)Supply voltage: 4.5–20 V DC (5 V typical, onboard 3.3 V regulator); Quiescent current: < 50 µA; Output level: 3.3 V HIGH / 0 V LOW
Hall effect sensor module (KY-003, A3144, 3-pin)Sensor IC: A3144 unipolar Hall-effect switch; Supply voltage: 4.5–24 V (A3144 rating; 5 V typical); Supply current: ≈4.4 mA typical (chip)
DS18B20 temperature sensor (1-Wire, TO-92)Supply voltage: 3.0–5.5 V (or parasite power from DQ); Interface: 1-Wire, unique 64-bit ROM code per sensor; Pull-up on DQ: 4.7 kΩ to VDD
MPU6050 accelerometer/gyro module (GY-521, I2C)Board supply: 3.3–5 V (onboard 3.3 V regulator); Chip supply: 2.375–3.46 V; Interface: I2C, up to 400 kHz
Rotary encoder module (KY-040, 5-pin)Supply voltage: 3.3–5 V; Output: 2-channel quadrature (CLK, DT); Pull-ups: 10 kΩ on CLK and DT; none on SW
BMP280 / BME280 barometric module (GY-BMP280, I2C/SPI)Board supply: GY-BMP280-3.3: 3.3 V only; boards with LDO: 3.3–5 V; Chip supply: 1.71–3.6 V; Interface: I2C (up to 3.4 MHz) or SPI (up to 10 MHz)
MQ-2 gas sensor module (4-pin)Supply voltage: 5 V; Heater resistance: 33 Ω ±5 %; Heater current: ≈150 mA