current-monitor

Overview

The current-monitor node measures electrical current by reading the voltage drop across a shunt resistor via an ADC. It supports configurable sample averaging for stable readings and computes current in milliamps and power in milliwatts. Essential for energy monitoring, load profiling, and overcurrent detection in IoT deployments.

Properties

Output

{
  "current_mA": 523.4,
  "voltage_mV": 52.34,
  "power_mW": 6280.8,
  "shuntResistor": 0.1,
  "samples": 4,
  "timestamp": 1640000000000
}

Wiring

  V_supply (+)
      |
      +---→ AIN0 (high side)
      |
    [R_shunt] 0.1Ω
      |
      +---→ AIN1 (low side)
      |
    [LOAD]
      |
     GND

  V_shunt = I_load * R_shunt
  Example: 1A * 0.1Ω = 100mV

Example: Energy Consumption Tracker

Accumulate energy usage over time and compute cost estimates.

// Function node: Energy accumulator
var current_mA = msg.current_mA;
var power_mW = msg.power_mW;
var now = Date.now();

var state = flow.get('energyState') || {
    totalEnergy_Wh: 0,
    lastTimestamp: now,
    peakCurrent_mA: 0
};

// Calculate energy consumed since last reading
var elapsed_h = (now - state.lastTimestamp) / 3600000;
var energy_Wh = (power_mW / 1000) * elapsed_h;
state.totalEnergy_Wh += energy_Wh;

// Track peak current
if (current_mA > state.peakCurrent_mA) {
    state.peakCurrent_mA = current_mA;
}

state.lastTimestamp = now;
flow.set('energyState', state);

// Cost estimate (configurable rate)
var rate_per_kWh = 0.12;
var cost = (state.totalEnergy_Wh / 1000) * rate_per_kWh;

msg.payload = {
    current_mA: current_mA.toFixed(1),
    power_mW: power_mW.toFixed(1),
    totalEnergy_Wh: state.totalEnergy_Wh.toFixed(3),
    peakCurrent_mA: state.peakCurrent_mA.toFixed(1),
    estimatedCost: cost.toFixed(4)
};

return msg;

Example: Overcurrent Protection Alert

Detect overcurrent conditions and send immediate alerts.

// Function node: Overcurrent detector
var current_mA = msg.current_mA;
var maxCurrent_mA = 5000; // 5A threshold

var alerts = flow.get('currentAlerts') || [];

if (current_mA > maxCurrent_mA) {
    var alert = {
        type: "overcurrent",
        current_mA: current_mA,
        threshold_mA: maxCurrent_mA,
        timestamp: msg.timestamp,
        message: "Current exceeded " + maxCurrent_mA + "mA: " + current_mA.toFixed(0) + "mA"
    };

    alerts.push(alert);
    flow.set('currentAlerts', alerts);

    msg.payload = alert;
    msg.topic = "alerts/overcurrent";
    return msg;
}

return null; // No alert needed

Common Use Cases