Realize a family security and environmental monitoring system (I)

One 、 System requirements analysis and overall design

1.1 System functional requirements analysis

（1） Use ESP8266 Connect the temperature and humidity sensor 、 Smoke sensor 、 Flame sensor 、 Infrared sensor of human body 、 Ultrasonic distance sensor , Real time collection of family environment , Relevant data is displayed on the screen .
（2）ESP8266 Be able to establish a connection with the cloud , Data can be uploaded to the cloud in real time .
（3） It can make local audible and visual alarm in time for the abnormal information of the monitored family environment , Warn people around , And it can remotely receive real-time alarm information at home from a special window on mobile wechat .
（4） Users can view the real-time environmental conditions in the home and the real-time picture of video monitoring outside the door through wechat applet without being at home .

1.2 Overall design of system structure

The overall architecture of the system ：

chart 1 The overall architecture of the system

System function block diagram ：

chart 2 System function block diagram

     The overall goal of the system is to adopt ESP8266-NodeMCU The control core collects the required environmental data through sensors , The network will MCU The collected data is uploaded to the cloud server , Family members can monitor the internal environment of the family and the real-time video surveillance image outside the door in real time through wechat applet .MCU Be able to perceive the security warning information inside the family in time , It also gives audible and visual alarm and can receive sudden warning messages in time in the security message receiving window of the user's wechat . Form a good real-time 、 Simple deployment 、 Low cost home security and environmental monitoring system .

Two 、 The hardware design of the system

2.1 Overall design of system hardware

     The hardware part of this system mainly includes two parts , First, data acquisition , Second, family security . Among them, data acquisition is a very important part of this system , Its main function is to collect environmental parameters in the environment ; Family security , The main function of this part is to alarm some dangerous situations of the family and to view the video monitoring outside the home remotely .
     The data acquisition module is mainly used to collect environmental data in the family , The collected data mainly includes temperature and humidity 、 Combustible gas smoke concentration 、 The distance between the door and the ultrasonic distance sensor 、 flame 、 Human body infrared , It can monitor the safety of the home environment in real time . The control core of the whole hardware is ESP8266 controller , because ESP8266 It has both data processing and WiFi Wireless capabilities , therefore ESP8266 Connect WiFi After that, the collected sensor data can be uploaded to the cloud in real time .
     Through buzzer and LED Light these two hardware to carry out local audible and visual alarm , It also pushes alarm messages in real time through wechat notification ; The hardware to realize remote video surveillance is ESP32-CAM modular , This module includes a OV2640 camera , There is no connection with ESP8266 The development board has a direct connection to the hardware , only ESP32-CAM The development board and a camera module constitute the hardware part of the remote monitoring .
     The hardware design also includes a OLED display , The display screen is mainly used to display the collected environmental data and some alarm information . The hardware structure block diagram of home security and environmental monitoring is shown in Figure 3 Shown .

chart 3 Hardware structure block diagram of home security and environment detection system

2.2 Selection and introduction of main control chip

     The control core of this system is ESP8266 chip , For development convenience , Use ESP8266-NodeMCU The development board is the control board of the system , The system also uses ESP32-CAM The module is used as a camera module for remote monitoring ,ESP32-CAM The core of the module is ESP32 chip . among ESP8266-NodeMCU Responsible for the collection and upload of family environment data 、 Audible and visual alarm and OLED Screen display ,ESP32-CAM The development board is mainly responsible for the realization of remote monitoring function .

2.2.1 ESP8266-NodeMCU Development board

    ESP8266-NodeMCU The main control chip of the development board is ESP8266. It is 32 Bit miniature MCU, with 16 Bit reduction mode , Main frequency support 80 MHz and 160MHz, Integrated WiFi function .
    ESP8266 Processor plus WiFi Antenna and so on ESP12-F WiFi modular ,ESP8266-NodeMCU The development board is in ESP12-F WiFi Extended on the basis of modules .ESP8266 It can be done by GPIO Port connected sensors and other application specific devices , This depends on its powerful storage capacity and on-chip processing capacity , Greatly reduce the cost of early development .ESP-12F WiFi The schematic diagram of the module is shown in the figure 4 Shown ：

chart 4 ESP-12F Schematic diagram

    ESP8266-NodeMCU It's an open source IoT Internet of things development board , Because it supports WIFI Function and with Arduino The use of development boards is very similar , You can use it directly Arduino IDE Software development , Greatly simplifies the development process . The design of this project is a project of Internet of things , Use ESP8266-NodeMCU The cost of development board is not high , Than raspberry pie and Arduino The family's IoT Platforms have more advantages .

ESP8266-NodeMCU Pin figure ：

chart 5 ESP8266-NodeMCU Pin figure

2.2.2 ESP32-CAM modular

     Because the data flow of the camera exceeds ESP8266 The computing power of microcontroller , Therefore, the video monitoring function of this system adopts ESP32-CAM Module to complete . This module is a small camera module launched by anxinco .

chart 6 ESP32-CAM Appearance drawing

ESP32-CAM The main features ：

• use 32 Bit low power dual core CPU
• The main frequency can reach 240MHz, The highest computing power can reach 600 DMIPS
• External 8MB PSRAM, Built in 520KB SRAM
• The supported interface types are SPI/UART/PWM/ADC/I2C/DAC
• The supported camera types are OV2640 and OV7670
• Support TF card
• Support STA/AP/STA+AP Working mode
• Support Smart Config/AirKiss One key distribution network , wait …

2.3 Sensor selection and control introduction

2.3.1 Temperature and humidity sensor

Scheme 1 ：
     choice DS18B20 Temperature sensor , It's smaller , It is widely used in equipment with small space . Microprocessor and DS18B20 The temperature sensor can realize two-way communication, and the sensor and MCU Only one is needed when connecting IO Line , The measurement results are as follows 9-12 Serial transmission for digital quantity . But because it can only detect temperature , Single function , Therefore, this scheme is not adopted .
Option two ：
     choice DHT11 sensor , The sensor is a calibrated digital signal output sensor , Only one IO mouth , Easy to program , The important thing is to save MCU Of IO resources .DHT11 There are resistive humidity sensing elements and NTC Temperature measuring element , Combined with temperature and humidity sensing technology and special digital module acquisition technology , Its reliability and stability are greatly improved , It has completely calibrated the measured data , Direct digital output . Self 4 One pin can realize power supply and data transmission without additional component connection , And low power consumption 、 Cost effective features .
     In many ways , choose DHT11 It is suitable as a sensor for measuring ambient temperature and humidity .

DHT11 The relevant parameters of temperature and humidity sensor are shown in the table below 3.1 Shown ：

type	Parameters
Working voltage	3.3V-5V
Temperature measurement range	-20℃~+60℃
Temperature measurement error	±2℃
Humidity measurement range	20% ~ 95%（0~50℃）
Humidity measurement error	±5%

DHT11 The physical drawing of temperature and humidity sensor module is shown in the figure 7 Shown , The internal circuit schematic diagram is shown in the figure 8 Shown ：

chart 7 DHT11 A physical picture

chart 8 DHT11 Module internal circuit diagram

     It can be seen from the schematic diagram DHT11 Sensors and MCU Connection method of ：1 Pin and VCC Pick up ,2 Pin connection DATA,3 Pin for NC Pin , In the air ,4 Pin connection GND, In the power supply and DATA Add a pull-up resistor between pins to improve stability . In this design DHT11 Sensor module DATA Pin connection ESP8266-NodeMCU Of D0（GPIO16） Pin for data transmission .

3.3.2 Flame sensor

chart 9 Physical drawing of flame sensor

chart 10 Schematic diagram of flame sensor

The physical drawing of the selected flame sensor is shown in the figure above 9 Shown . The schematic diagram is shown in the figure 10 Shown
The main parameters of the sensor are as follows ：

• The wavelength range of flame that can be detected is 760 nanometer ~1100 nanometer
• Detection angle 60 Degrees or so
• The sensitivity can be adjusted
• The working voltage is 3.3~5V
• Digital switching value （0 or 1） Output

     In this design, the flame sensor module D0 Pin connection ESP8266-NodeMCU Of D3（GPIO0） Pin for data transmission , adopt D0 The level of pin output determines whether flame is detected .

2.3.3 Smoke sensor

     In modern home life , Combustible gases such as natural gas greatly facilitate people's life , In case of leakage, it may cause serious harm . If these leaked gases encounter open flames again , There will be terrible consequences such as fire and explosion . In order to detect whether the combustible gas in the home leaks , choice MQ-2 Smoke sensors detect the concentration of natural gas smoke in the home environment , It is of great significance to ensure the indoor safety of families .

chart 11MQ-2 Physical drawing of smoke sensor

    MQ-2 Type a gas sensor uses tin oxide （SnO2） As a combustible gas sensing material , Tin dioxide has less conductivity in clean air , In contact with flammable gases , Its conductivity is positively correlated with the concentration of combustible gases in the air , With the increase of flue gas concentration and conductivity , Its output value will also increase .MQ-2 Type a gas sensor for liquefied gas 、 alkane 、 Hydrogen and other combustible gases are highly sensitive , It can effectively detect the combustible gas in the surrounding air , It has good anti-interference . The sensor has the ability to measure various flammable gases , It is a low-cost sensor , Suitable for many occasions .

MQ-2 Sensor parameters ：

type	Parameters
Detect gas	Combustible gas 、 smoke
Working voltage	2.5V-5V
Heating power	≤900mW
Detection range	3000-10000ppm

     In a safe situation , The smoke concentration in the home is maintained in a normal range , therefore , You can set an upper limit on the smoke concentration in your home , When MQ-2 The smoke concentration detected by the smoke sensor exceeds this upper limit , It will trigger the operation of the alarm system , Convey the corresponding alarm information to people .

MQ-2 The schematic diagram of the module is shown in the figure below 12：

chart 12 MQ-2 Schematic diagram

     In this system ,MQ-2 The gas sensor uses only three pins ,VCC Connect the positive pole of the power supply ,GND Grounding , Analog interface AOUT Pick up ESP8266 Of A0 Interface .ESP8266-NodeMCU By reading the MQ-2 Simulate the value of the port to judge whether the natural gas in the home leaks .

2.3.4 Infrared sensor of human body

chart 13HC-SR312 A physical picture

     To prevent burglary , Pyroelectric infrared sensor is used for monitoring , Pyroelectric infrared sensor has high cost performance , Sensitive and anti-interference , It can effectively prompt people to detect someone nearby , It can play the role of family theft prevention .
     Combined with ESP8266-NodeMCU The output voltage is 3.3V, Pyroelectric infrared sensor that can work normally under this voltage is selected ,HC-SR312 The human body sensor module meets this requirement , chart 3.11 It is the physical picture . This module can realize automatic induction , When someone enters the sensing area HC-SR312 The output pin of outputs high level , Output low level when leaving the sensing area or no one enters the sensing area .

HC-SR312 Parameter list of human body induction module ：

type	Parameters
Working voltage	2.7-12V
Delay Time	2 second
Blockade time	2 second
Trigger mode	repeatable
Sensing range	≤ 100 Degree cone angle ,3-5 rice
working temperature	-20℃~+60℃
Dimensions	10mm×8mm

Functional characteristics ：

（1） It has good anti-interference performance . Its interior is processed by digital signals , Can be high 、 The low level is directly output from the outside ;
（2） Repeatable trigger mode . After sensing human activity output high level , Within a certain delay period , If there is activity within its perceptual range , Then its output will always be maintained at high level , Until the person leaves the sensing range and the delay ends , Will become low level .

     In this design HC-SR312 Human body induction module OUT Pin connection ESP8266-NodeMCU Of D5（GPIO14） Pin for data transmission . The method of flame detection is the same as that of the previous flame sensor , By judgment OUT The level of the pin determines whether someone is active in the current sensing area .

2.3.5 Ultrasonic ranging sensor module

The model of ultrasonic distance sensor selected in this system design is HC-SR04, The physical picture is shown in the picture 14 Shown .

chart 14 Physical drawing of ultrasonic distance sensor

chart 15 HC-SR04 Schematic diagram

working principle ：
（1） use 10us High level signal triggers ranging ;
（2） The module sends out ultrasonic waves , And can automatically detect whether there is echo ;
（3） Ultrasonic signal detected bouncing , Will pass immediately I/O Pin output high level , The time from the emission to the return of ultrasonic wave is the duration of high level . The test distance =( High level time * The speed of sound (340M/S))/2.

Working parameters ：

• Working voltage ：3.3V-5V
• Quiescent current ： Less than 2mA
• Detection angle ： No more than 15°
• Detection distance ：2cm-450cm
• Highest accuracy ： Can be up to 0.3cm
• working temperature ：-20℃~80℃

2.4 Introduction to selection and control of display module

     In the field of electronic design , The display screen is often used to display data and important messages . Common screen displays are LED The nixie tube shows ,OLED Display and TFT-LCD The screen shows , Here is a brief analysis ：
（1）LED The nixie tube shows
    LED The nixie tube can only display numbers or characters , And occupy I/O Too many resources , Can't display the Chinese characters or pictures we want .
（2）TFT-LCD screen
    TFT-LCD It is the mainstream display screen in the market , This kind of screen can support higher digit color depth , It can also support RGB Color mode , Some can also support touch , The function is all ready . All design requirements are TFT-LCD The requirements of the subject can be realized on the screen , But considering power consumption, size, appearance and other factors , It's not as light and compact as the one with lower power consumption OLED The screen is more suitable for this design .
（3）OLED The screen shows

chart 16 OLED Physical picture of display screen

     More mainstream in the market OLED The screen is 0.96 " OLED display （ Pictured 16） and 1.3 " OLED display , This kind of display adopts the organic diode light-emitting principle , Less materials are needed , It can withstand low temperature , Low power consumption , These two paragraphs OLED The screen can meet the requirements of displaying pictures 、 Chinese characters 、 English and other characters , The resolution can also meet the requirements , The screen interface style is simple , Small and light , It is very suitable as the display module of this topic .

Its schematic diagram is shown in the figure below 17 Shown ：

chart 17 OLED Schematic diagram of screen

    OLED Of SCL and SDA The pins are connected separately ESP8266-NodeMCU Of D1（GPIO5） and D2（GPIO4） Pin , Conduct IIC signal communication .

2.5 Sound and light alarm hardware design

    （1） Buzzer is a common sounding element in electronic design , Widely used in electronic equipment . In the system design of this subject , Buzzer is mainly used to give audible alarm for relevant abnormalities . There are two main types of buzzers , One is an active buzzer , The other is a passive buzzer .
     The active buzzer has a vibration source inside , You can make it sound just by applying direct current ; There is no vibration source inside the passive buzzer , DC cannot make it sound , need PWM Drive sound .

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chart 18 The actual picture of buzzer

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chart 19 Schematic diagram of buzzer

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     On the premise that the program is not too complex and the sound alarm effect can be achieved , It is more appropriate to choose the active buzzer as the alarm in this design . Its I/O Pin connection ESP8266-NodeMCU Of D6（GPIO12） Pin , Write a low level to it to sound .
    （2） The light part of audible and visual alarm is red LED As a light source . Just power on the alarm when it is needed .

2.6 PCB draw

2.6.1 Schematic drawing

chart 20 ESP8266 Schematic diagram of the expanded version

2.6.2 PCB Make

     Combine the schematic diagram in Lichuang EDA In software PCB Design , The circuit connection between various components is shown in the figure below 21 Shown .

chart 21 PCB Internal wiring

Set teardrops and lay copper ：

chart 22 The front is paved with copper

chart 23 The reverse side is covered with copper

PCB After the design 3D Preview ：

chart 24 PCB 3D Preview

3、 ... and 、 Software design of the system

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