Scenario: Smoke Alarm + Buzzer + MQTT Report

Scenario Description

Use an MQ-2 smoke sensor to collect smoke concentration via ADC. When the concentration exceeds a set threshold, trigger a buzzer alarm and report device alarm events to the IoT platform via MQTT, achieving both local and remote dual alarm.

Hardware List

Module	Model	Qty	Wiring
Smoke Sensor	MQ-2	1	AO→GPIO34
Buzzer	Active buzzer module	1	IN→GPIO25
LED Indicator	Red LED	1	→GPIO2 (onboard)

Complete Configuration Process

Method 1: Web Interface Configuration (Recommended)

This scenario requires first adding the smoke ADC, buzzer, and indicator LED, then using peripheral execution rules for threshold alarm and MQTT reporting.

The smoke alarm scenario is broken down in a closed loop: ADC collects concentration, rule evaluates threshold, buzzer and indicator execute actions, MQTT reports alarm event.

Step 1: Configure Peripherals

Step 1: Open Peripheral Management Page

1. Open a browser and navigate to the ESP32 IP address
2. After logging in, click Peripheral Configuration in the left menu

Step 2: Add MQ-2 Smoke Sensor

1. Click the Add Peripheral button

2. Fill in the configuration:

   Field	Value	Description
   Peripheral ID	smoke_sensor	Smoke sensor MQ2
   Name	Smoke Sensor MQ2	Display name
   Peripheral Type	GPIO Analog Input (type: 15)	ADC collection
   Pin Configuration	34	AO connected to GPIO34 (ADC1)
   Attenuation	11dB (3)	0-3.3V range
   Resolution	12-bit	0-4095
   Sample Rate	5	5Hz

3. Click Save

Step 3: Add Alarm Buzzer

1. Click the Add Peripheral button again

2. Fill in the configuration:

   Field	Value	Description
   Peripheral ID	buzzer_01	Alarm buzzer
   Name	Alarm Buzzer	Display name
   Peripheral Type	GPIO Digital Output (type: 12)	Buzzer control
   Pin Configuration	25	IN connected to GPIO25
   Initial State	0	Default off

3. Click Save

Step 4: Add Alarm LED

1. Click the Add Peripheral button a third time

2. Fill in the configuration:

   Field	Value	Description
   Peripheral ID	led_alarm	Alarm LED
   Name	Alarm LED	Display name
   Peripheral Type	GPIO Digital Output (type: 12)	LED control
   Pin Configuration	2	Onboard LED
   Initial State	0	Default off

3. Click Save

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Step 2: Configure Peripheral Execution Rules

Rule 1: Timed Smoke Concentration Collection

1. Click Peripheral Execution in the left menu

2. Click the Add Rule button

3. Fill in basic configuration:

   • Rule Name: Smoke Concentration Collection
   • Report Data: ✅ Enabled
   • Enable: ✅ Enabled

4. Configure trigger:

   • Trigger Type: Select Timer Trigger
   • Timer Mode: Select Fixed Interval
   • Interval Time: 5 (5 seconds; smoke detection requires high response speed)

5. Configure action:

   • Action Type: Select Sensor Read
   • Target Peripheral: Select smoke_sensor
   • Data Field: analog

6. Click Save

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Rule 2: Smoke Exceedance Alarm

1. Create rule, name: Smoke Exceedance Alarm

2. Trigger configuration:

   • Trigger Type: Select Event Trigger
   • Event ID: Enter ds:smoke_sensor_analog
   • Operator: Select Greater Than (>)
   • Threshold: 2000 (ADC value, approximately medium smoke concentration)

3. Action configuration (3 actions needed):

   • Action 1: Select Flash, target buzzer_01, interval 300 (300ms rapid beeping)
   • Action 2: Select Flash, target led_alarm, interval 500 (500ms flashing)
   • Action 3: Select Trigger Event, event ID smoke_alarm

4. Click Save

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Rule 3: Smoke Back to Normal

1. Create rule, name: Smoke Back to Normal

2. Trigger configuration:

   • Trigger Type: Select Event Trigger
   • Event ID: Enter ds:smoke_sensor_analog
   • Operator: Select Less Than (<)
   • Threshold: 1000 (below alarm threshold, forming hysteresis)

3. Action configuration (2 actions needed):

   • Action 1: Select Low Level, target buzzer_01
   • Action 2: Select Low Level, target led_alarm

4. Click Save

💡 Tip: Alarm threshold 2000, recovery threshold 1000, forming a 1000 hysteresis band to prevent repeated alarming

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Method 2: JSON Configuration File Import

Working Principle

• MQ-2 sensor outputs analog voltage; higher smoke concentration = higher voltage
• ADC reading range 0~4095 (corresponding to 0~3.3V)
• Threshold 2000 approximately corresponds to medium smoke concentration (needs calibration based on actual environment)
• Recovery threshold 1000 forms hysteresis to avoid repeated alarming near the threshold

Parameter Adjustment

Parameter	Recommended Value	Description
Collection Interval	5s	Smoke detection requires higher response speed
Alarm Threshold	2000	Raw ADC value; needs calibration based on environment
Recovery Threshold	1000	Below alarm threshold, forming hysteresis band
Buzzer Flash Interval	300ms	Rapid beeping to indicate danger

Precautions

1. MQ-2 sensor requires 5~10 minutes preheat time to stabilize
2. New sensor should be preheated for over 24 hours before first use
3. Alarm threshold needs calibration based on actual environment and application scenario
4. Regular sensor maintenance is recommended (dust accumulation affects sensitivity)