Overview
The hcsr04 node measures distance using ultrasonic sensors like the HC-SR04.
It sends ultrasonic pulses and measures the echo return time to calculate distance. Ideal for
level monitoring, parking sensors, and proximity detection.
2-400cm
Range
3mm
Resolution
15°
Angle
5V
Power
Voltage Level Warning
HC-SR04 ECHO pin outputs 5V. Use a voltage divider (1kΩ + 2kΩ) to protect the Pi's 3.3V GPIO pins!
Wiring with Voltage Divider
HC-SR04 Connection
VCC → 5V
TRIG → GPIO 23
ECHO → Voltage Divider → GPIO 24
GND → GND
Voltage Divider
ECHO → 1kΩ → GPIO 24
GPIO 24 → 2kΩ → GND
This drops 5V to ~3.3V (safe for Pi)
Properties
| Property | Type | Default | Description |
|---|---|---|---|
| trigPin | number | 23 | GPIO pin for TRIG |
| echoPin | number | 24 | GPIO pin for ECHO |
| interval | number | 1000 | Measurement interval (ms) |
| unit | string | "cm" | "cm", "m", or "inch" |
| median | number | 3 | Number of readings to average |
Output
{
"payload": 45.2,
"unit": "cm",
"raw": 45234,
"timestamp": 1640000000000
}Example: Water Tank Level Monitor
Monitor water tank level and alert when low.
// Function node: Calculate tank level
const TANK_HEIGHT = 100; // cm from sensor to bottom
const TANK_CAPACITY = 500; // liters
var distance = msg.payload; // distance to water surface
var waterHeight = TANK_HEIGHT - distance;
var percentFull = (waterHeight / TANK_HEIGHT) * 100;
var liters = (percentFull / 100) * TANK_CAPACITY;
msg.payload = {
distance: distance,
waterHeight: waterHeight.toFixed(1),
percentFull: percentFull.toFixed(0),
liters: liters.toFixed(0),
status: percentFull < 20 ? "LOW" : percentFull < 50 ? "MEDIUM" : "OK"
};
return msg;