interrupt

Overview

The interrupt node handles hardware interrupts for time-critical GPIO events. Unlike polling-based gpio-in, interrupts respond immediately to signal changes, making them ideal for encoders, pulse counting, and precise timing applications.

Interrupt vs Polling

Properties

Common Use Cases

Example: Rotary Encoder with Direction

Track position and direction of a quadrature rotary encoder.

// Function node for quadrature decoding
// Connect Channel A to GPIO 17 (interrupt node)
// Connect Channel B to GPIO 27 (read in function)

var pinB = 27; // Hardcode for this example
var lastA = context.get('lastA') || 0;
var position = context.get('position') || 0;

// Read current state of both channels
var stateA = msg.payload;
var stateB = global.get('gpio_' + pinB) || 0;

// Determine direction based on B when A changes
if (msg.edge === 'rising') {
    if (stateB === 0) {
        position++; // Clockwise
    } else {
        position--; // Counter-clockwise
    }
} else if (msg.edge === 'falling') {
    if (stateB === 1) {
        position++; // Clockwise
    } else {
        position--; // Counter-clockwise
    }
}

context.set('position', position);

msg.payload = {
    position: position,
    direction: (position > context.get('lastPos')) ? 'CW' : 'CCW'
};
context.set('lastPos', position);

return msg;

Example: Flow Meter

Calculate water flow rate from Hall effect sensor pulses.

// Function node: Calculate flow rate
// YF-S201 flow sensor: 7.5 pulses per liter

const PULSES_PER_LITER = 7.5;

// Use the frequency from interrupt node
var frequency = msg.frequency || 0;

// Calculate flow rate
var litersPerMinute = (frequency / PULSES_PER_LITER) * 60;

msg.payload = {
    flowRate: litersPerMinute.toFixed(2),
    unit: "L/min",
    totalPulses: msg.count,
    totalLiters: (msg.count / PULSES_PER_LITER).toFixed(2)
};

return msg;

Troubleshooting