Example 35: Smoke Sensor (MQ-2)

Experiment Overview

The MQ-2 gas sensor detects combustible gases (LPG, propane, hydrogen) and smoke concentration, outputting an analog signal. Suitable for kitchen gas leak alarms, smoke fire alarms, and other safety scenarios.

Hardware Wiring

Board Label	GPIO Pin	Connected Device
AO	GPIO34	MQ-2 analog output
DO	GPIO4	MQ-2 digital output (over-threshold alarm)

MQ-2 requires 1-2 minutes of preheating before readings stabilize.

JSON Configuration Example

{
  "peripherals": [
    {
      "id": "smoke_01",
      "name": "MQ-2 Smoke",
      "type": 15,
      "enabled": false,
      "pins": [34],
      "params": {}
    }
  ]
}

Peripheral Execution Linkage

Scenario: Smoke Alarm (Polling Trigger)

Feature: Trigger buzzer alarm when smoke concentration is too high (ADC > 2000)

Web UI Configuration Steps

Step 1: Ensure Buzzer Peripheral is Configured

• Peripheral ID: buzzer_gpio
• Type: GPIO Output

Step 2: Create Rule

1. Click Peripheral Config in the left menu → Switch to Peripheral Execution tab
2. Click New Rule button
3. Fill in basic configuration:
   • Rule Name: Smoke Alarm
   • Report Data: ✅ Enabled
   • Enable: ✅ Enabled

Step 3: Configure Trigger (Polling Trigger)

1. Click Add Trigger button

2. Fill in trigger configuration:

   Field	Value	Description
   Trigger Type	Select Polling Trigger	Periodic condition check
   Target Peripheral	Select smoke_01	MQ-2 smoke sensor
   Polling Interval	2000	2 seconds
   Condition Expression	value > 2000	Smoke concentration threshold

Step 4: Configure Actions (2 actions required)

Action 1: Buzzer Alarm

1. Click Add Action button
2. Fill in:
   • Action Type: Select HIGH
   • Target Peripheral: Select buzzer_gpio

Action 2: Send Alarm Event

1. Click Add Action button again

2. Fill in:

   • Action Type: Select Send Event
   • Event Type: alarm
   • Event Message: Smoke concentration too high!

3. Click Save button

MQ-2 Sensor Specifications

Feature	Description
Detectable Gases	LPG, propane, hydrogen, smoke
Preheat Time	24-48 hours first time, 1-2 minutes daily
Power Consumption	~800mW (heating element)
Lifespan	~2-5 years
Cross-Sensitivity	Also responds to alcohol, acetone

Notes

1. Preheating: First power-on requires 24-48 hours preheating; daily use requires 1-2 minutes warm-up
2. Power Consumption: Heating element consumes ~800mW; stable 5V power supply required
3. Cross-Sensitivity: Also responds to alcohol, acetone, etc.; not smoke-specific
4. Calibration: Record baseline value in clean air as alarm threshold reference
5. Lifespan: Sensor lifespan is ~2-5 years; sensitivity gradually decreases