[IOT design. Part I] stm32+ smart cloud aiot+ laboratory security monitoring system

1   System content requirements

（1） Measure the temperature and humidity in the Laboratory 、 Smoke concentration 、 Propane concentration ;
（2） Check the water leakage on the ground , If there is water leakage, start the water pump to drain ;
（3） Detect door and window intrusion ;
（4） It has a variety of alarm modes ;
（5） mobile phone APP Remote control .


2   Component selection


 

3   System hardware design
3.1 Hardware component block diagram
3.1.1 The main control hardware is composed of

The main control circuit is shown in the figure 3.1 Shown , It consists of the following parts ： With STM32 As a processing center , Smoke sensor measures smoke concentration , Propane sensor measures propane concentration , The temperature and humidity sensor measures the temperature in the air 、 humidity , The Bluetooth host receives the data sent by the auxiliary control , Fan 1 circuit 、 Fan 2 circuit 、 The audible and visual alarm circuit triggers when the conditions are met ,4G The module transmits the measured data to the cloud server , Receive mobile phones at the same time APP Downlink command of .




chart 3.1 Main control hardware composition


3.1.2 The auxiliary control hardware is composed of

The auxiliary control circuit is shown in the figure 3.2 Shown , It consists of the following parts ： With STM32 As a processing center , The water immersion sensor detects whether there is water leakage on the ground , The human body sensor senses whether someone has passed , The Bluetooth slave sends the information collected by the auxiliary control to the master , Audible and visual alarm circuit 、 The water pump circuit triggers when the conditions are met .






chart 3.2 Composition of auxiliary control hardware


3.2 Human body sensor

Choose human body sensor HCSR505 To sense whether someone has passed , So as to judge the intrusion of doors and windows [2]. The sensor is based on infrared , When someone moves within the sensing angle , It will output high level , The delay time is 8 second , Otherwise, it is low level . As shown in the table 3.1 You can know some parameters of human body sensor , Its working state can also be selected , Suitable for different occasions .
surface 3.1 HCSR505 Product parameter table






As shown in the table 3.2 Shown , You know you should give VCC Pick up 5V Voltage supply , then GND Grounding is common ,OUT The pin is connected to the pin of MCU , The wiring circuit is shown in the figure 3.3 Shown . When someone moves within the sensing range , It will change the detection distance of the infrared spectrum , The signal pin outputs a high level , Conversely, low level . By reading the pin status of the connected MCU , You can know if anyone has passed , So we can know the invasion of the doors and windows of the Laboratory .

chart 3.3 HCSR505 Wiring diagram


3.3 Electrode type water immersion probe

Select a water immersion probe to detect whether there is water leakage on the key ground , The electrode type water immersion probe is used , The probe is contact , It means that it can sense only when it is in contact with water . As shown in the table 3.3 Shown , The working state and material of electrode type water immersion probe can be understood .


surface 3.3 Product parameters of water immersion sensor






chart 3.4 Wiring diagram of water immersion sensor


From the figure 3.4 It can be seen that , Working principle of water immersion sensor , When the probe of the water immersion sensor detects water , The signal passes through the conversion circuit , The voltage of the collector of the triode is low , If there is no water, the output is high . Connect the output end to the pin of the MCU , By reading the status of this pin , Then you can know whether there is water leakage on the ground , If water leaks, turn on the water pump , Do not open if there is no .


3.4 Bluetooth wireless module

Select Bluetooth module HC05 To communicate with the main control and auxiliary control , Connect via Bluetooth , You can send data to each other , Data transmission [12]. The working state and working principle of Bluetooth module can be found through parameter setting , The basic parameters are shown in table 3.4 Shown .
surface 3.4 Bluetooth module HC05 Parameter description of








chart 3.5 HC05 Wiring diagram


By the table 3.5 You can know the Bluetooth module HC05 The wiring method of the system . For the moment , The connection between Bluetooth and MCU only needs to be connected 4 Line ,VCC Connect 5V,GND Grounding , The receiving end of Bluetooth is connected to the serial port of MCU 1 The sender of , The sending end is connected to the serial port of the MCU 1 The receiving end of , Pictured 3.5 Shown .

3.5 Audible and visual alarm circuit

utilize NPN Type a crystal triode S9012 As the core of control , When the single chip microcomputer gives instructions to low level 0V when , The emitter of the triode E by 5V, The base B by 0V, The condition of triode conduction is the base B And the emitter E The voltage difference between them exceeds 0.7V that will do , So give 0V Low level meets this condition , Triode conduction , The LED meets the conduction conditions and lights up . After the triode is turned on , The voltage difference between the positive and negative poles of the buzzer is about enough , Meet the voltage difference required for operation 3V, Sound the alarm . If the single chip microcomputer gives a high level , It doesn't meet the condition of triode conduction , The LED doesn't work , There is no voltage difference between the positive and negative poles of the buzzer and they are mute . The audible and visual alarm circuit is shown in the figure 3.6 Shown .





3.6 Relay circuit

The type of relay used is SRD-05V-DC-SL-C, It has 5 One pin ： Input pin 1、 Input pin 2、 Public end 3、 The constant beginning 4、 Normally closed end 5.1、2 Pin connection control voltage 5V, When the MCU gives a high level 3.3V When , Triode base B And the emitter E Meet the conduction voltage 0.7V, The LED meets the conduction conditions and emits light . The constant beginning 4 And public end 3 Conduction , The positive pole of the fan is connected to the constant start of the relay 4, Connect to the breadboard , At the beginning 4 And public end 3 After conduction , There is enough voltage to drive the fan , Otherwise, the normally closed end 5 And public end 3 Conduction , The fan does not have enough voltage to drive . diode IN4148 The function of is at the moment when the MCU gives high-level instructions , Avoid burning the triode due to the sudden increase of voltage . The relay circuit is shown in the figure 3.7 Shown .




chart 3.7 Relay circuit


3.7 Indicator circuit

For the laboratory safety monitoring system , Indicator circuit is indispensable , Pictured 3.8 Shown . When the MCU gives a high level , The LED turns on ; When giving low level , The LED is not conductive [5]. The high and low levels given by the single chip microcomputer are determined by the measured data . And the LED can't bear it directly 3.3V The voltage of , Therefore, resistance is needed to divide the voltage .






3.8 Gas sensor

Many people know that most metals have electrical conductivity , And the gas sensor uses this principle to measure the gas concentration , Different sensors have different conductivity for different gases [7]. such as MQ2 Smoke sensors are sensitive to the concentration of smoke in the air , Therefore, it is suitable for measuring smoke concentration .




chart 3.9  MQ2 Wiring diagram


By the table 3.7 You know , It is necessary to read the gas concentration in the Laboratory , Therefore, the analog signal output pin needs to be connected AO, And then through the internal AD Convert it into numbers and display it [9],GND Grounding ,VCC Connect 5V Power it [1], Pictured 3.9 Shown , Make it work . And another gas sensor MQ6 How it works 、 The same is true of the wiring diagram .
3.9 Temperature and humidity sensor


The pin description is shown in table 3.8 Shown , So just connect the positive and negative poles , Then connect the analog output pin . The wiring circuit is shown in the figure 3.10 Shown .



chart 3.10 DHT11 Circuit diagram


3.10 Power access circuit

For all products , Power supply is essential . Therefore, we need to connect the power supply with stable voltage , Pictured 3.11 Shown , It can be seen that the connected power base is P2, Can pass USB Power transfer DC The DC data line is directly connected to the usual household power supply , Supply the system with 5V electric . When 6 Foot self-locking switch SW1 When pressed , Pin 2、3 Conduction , The connected power supply can drive the laboratory safety monitoring system .




chart 3.11 Power access circuit


3.11 4G Module access circuit

about 4G The module says , It uses Cat module ML302 At the core , The supported frequency bands are LTE-TDD B34/B38/BB39/B40/B41、LTE-FDD B1/B3/B5/B8, Its average power consumption is 1W. It regularly sends data to the monitoring platform , Real-time monitoring [11]. The pin description is shown in table 3.9 Shown .






therefore , take 4G The module is connected to STM32 Minimum system board , take TXD、RXD Connect to the serial port 3 Reception 、 Send pin ,GND Connected to the SCM GND. At the same time, connect the positive pole of the lithium battery 4G Modular VCC, Power it , The negative pole is connected to the single chip microcomputer GND, Its wiring is shown in the figure 3.12 Shown .




chart 3.12 4G Module access circuit

The next chapter contains the following ：
4   System software design
4.1 SCM programming
4.1.1 SCM program development environment
4.2 mobile phone APP Programming
4.2.1 Timer timing program

5   mobile phone APP The design of the
5.1 Wit cloud AIoT The access process of