51 single chip microcomputer indoor environment monitoring system, mq-2 smoke sensor and DHT11 temperature and humidity sensor, schematic diagram, C programming and simulation

The design requirements

1. With 51 Single chip microcomputer is the control core , Temperature and humidity sensors and smoke sensors are used to collect and process indoor environmental data ;

2.LCD1602 LCD real-time display of temperature and humidity 、 Smoke concentration and other data ;

3. The user can set the upper and lower limit of temperature and humidity alarm threshold and smoke alarm threshold by pressing the key ;

4. When the indoor temperature and humidity are not within the set range 、 When the smoke concentration exceeds the limit , Buzzer and LED The lamp provides audible and visual alarm ;

System Overview
This paper designs a software based on MQ-2 and DHT11 Indoor temperature and humidity of the sensor - Smoke alarm system , It can realize the control of indoor temperature and humidity 、 Combustible gas / Real time monitoring and display of smoke concentration , It also provides early warning value setting and audible and visual alarm functions .

The system hardware mainly consists of AT89C52 Minimum system of single chip microcomputer 、MQ-2 Smoke sensor module 、DHT11 Temperature and humidity sensor module 、LCD1602 Display module 、 It is composed of key module and audible and visual alarm module , The system framework is as follows .

among ,AT89C52 Single chip microcomputer is the control core of the whole system , Used to receive 、 Process the information collected by the sensor , And send the processed information to LCD Real time display .

When indoor temperature and humidity 、 When the concentration of combustible gas or smoke exceeds the threshold set by the user , relevant LED The indicator light is on , The buzzer makes a sound .

Simulation circuit diagram

Schematic diagram

Simulation analysis
Open indoor temperature, humidity and smoke detection .pdsprj Simulation file for , Double click the MCU , Click the small yellow folder icon in the pop-up dialog window , load Monitor.hex file （ be located C In the program folder ）, Run the simulation , The effect is as follows .

It can be seen from the picture that ,LCD The first 1 Row display Monitor System（ The monitoring system ）, The first 2 The row shows that the current indoor temperature is 27℃, The humidity is 55%RH, The smoke concentration is 14%.LCD The displayed result is consistent with the value on the sensor , Indicates that the data sampling is correct .

adopt DHT11 On the sensor 3 A small red arrow simulates the change of indoor temperature and humidity . The first two small red arrows are used to increase or decrease the value , The last small arrow is used to switch between temperature and humidity .

because Proteus Simulation no MQ-2 Smoke sensor element , and MQ-2 The principle of the sensor is to convert the smoke concentration directly into the change of resistance , So here we use sliding rheostat to replace it .

Slide the rheostat by clicking RV2 Up and down red arrows , Simulate the change of indoor smoke concentration .

for example , We adjust the indoor temperature to 31℃, The humidity is 48%RH, The smoke concentration is 7%, give the result as follows .

The user can adjust the key 、 Increase and decrease keys to set the upper and lower limit of temperature and humidity alarm threshold and smoke alarm threshold .

Click the adjustment key , The system enters the upper and lower limits of temperature and humidity 、 Smoke alarm threshold setting interface , As shown in the figure below . among T Represents the temperature ,H Represents humidity ,S Represents smoke concentration .

The default temperature range of the system is ：20-35℃, The humidity range is ：40-85%RH, The smoke alarm threshold is ：15%.

After entering the setting interface , The lower temperature limit cursor flashes , At this time, you can add / Decrease the key to adjust the value , After adjustment , Continue to click the adjustment key , The cursor of the upper temperature value flashes , At this time, the upper limit value can be adjusted .

By analogy , After all parameters are set , Click the adjustment button again , You can exit the setting interface , Return to the system display interface .

for example , We set the temperature range to 28-36℃, The humidity range is 40-65%RH, The smoke alarm threshold is 5%.

When the system detects that the indoor temperature and humidity are not within the set upper and lower limits or the smoke concentration is greater than the alarm threshold , The buzzer beeps , Corresponding LED The light is on . When the indoor environment returns to normal , Alarm disarmed .

Return to the display interface , The system monitors that the current indoor smoke concentration is 7%, Greater than set 5%, At this time, the smoke alarm lamp is on , The buzzer makes a sound , Remind users to pay attention to .

in summary , The simulation results meet the design requirements .

part C Code

		while(KeySet_P)				 		// “ Set the key ” Not pressed , It is always in the setting of smoke limit 
		{
    
			if(KeyDown_P==0)		 		//  Judge  “ Minus button “  Is it pressed 
			{
    
				if(AlarmSK>0)			  	//  Only when the smoke limit is greater than 0 when , Can reduce 1
					AlarmSK--;
				LcdGotoXY(0,14);	 		//  Refresh to display the changed smoke limit 
				LcdPrintNum(AlarmSK);
				LcdGotoXY(0,15);			//  Reposition the flashing cursor position 
				DelayMs(350);
				while(!KeyDown_P);
			}
			if(KeyUp_P==0)				 	//  Judge  “ Add button “  Is it pressed 
			{
    
				if(AlarmSK<99)				//  Only when the smoke limit is less than 99 when , To add 1
					AlarmSK++;
				LcdGotoXY(0,14);	 			//  Refresh to display the changed smoke limit  
				LcdPrintNum(AlarmSK);
				LcdGotoXY(0,15);	 		//  Reposition the flashing cursor position 
				DelayMs(350);					//  Time delay 
				while(!KeyUp_P);
			}	
		}

		LcdWriteCmd(0x0C);	  		//  Cancel cursor blink 
		LcdShowInit();						//  The liquid crystal display is the... Of the detection interface 

		DelayMs(10);	  					//  Remove the jitter caused by key pressing 
		while(!KeySet_P);	 				//  Wait for the key to release 
		DelayMs(10);					  	//  Remove the jitter caused by key release 

Information content
（1） be based on MQ-2 and DHT11 Indoor temperature and humidity smoke alarm system design paper ;

（2）Proteus8.6 Simulation ;

（3）C Program ;

（4）AD Schematic diagram ;

（5）Visio flow chart ;

（6） Reference material ;

（7） List of components ;

Data figure






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