Design and Implementation of Intelligent Agricultural Greenhouse System

DHT11 sensor is a temperature and humidity composite sensor with calibrated digital signal output [7]. Its features include low cost, good stability, can also be used in harsh environment, fast response to these aspects. DHT11 adopts the serial mechanism. The circuit design of DHT11 module is shown in Figure 1.

Figure 1

This part uses the photosensitive sensor to form the light intensity module. Photosensitive sensors convert the optical signals into electrical signals by using the characteristics of photosensitive elements, and their response wavelengths are near visible wavelengths.

Generally, when detecting light intensity, photosensitive sensor is also often used as a device. If other signals are converted into optical signals and then through the photosensitive sensor, the parameter values of other signals can also be obtained. The photosensitive sensor used in this design is a photosensitive diode, whose structure is similar to the semiconductor structure, with a PN junction inside, so the photosensitive sensor also has one-way conductivity. Schematic diagram of optical intensity module is shown in Figure 2. LS1 is a photodiode and R58 provides it with a reverse voltage. When the light intensity changes, the voltage at both ends of LS1 will also change. The stronger the light intensity is, the lower the corresponding voltage will be; otherwise, the higher the light intensity is, the higher the corresponding voltage will be. The LIGHT SENSOR connects to the PF7 pin of the development board and uses the analog input function of the pin. At the same time, the onboard ADC3 channel is used to convert the collected analog signal into digital signal.

Figure 2

Infrared detection module HC-SR501 is an automatic control module using infrared technology [8]. This module works in the dc voltage range of 4.5–20V and can output TTL level. It has a working range of 7 m. It has two triggering modes: Non-triggering mode and repeatable trigger mode.

This module has inductive blocking time, that is, when the inductive output high level becomes low level, the developer can manually set a blocking time, during the blocking time, the infrared sensor does not receive any inductive signal. Therefore, it plays an important role in interval detection and effective suppression of various interferences in the process of load switching.

The OV2640 offers a single UXGA camera. Generally, OV2640 module is controlled by SCCB bus. The OV2640 can achieve a maximum frame rate of 15 frames per second if in output UXGA image mode. If through SCCB interface programming can achieve any image processing process [9]. The OV2640 module consists of the following modules: photosensitive array, analog signal processing, 10-bit A/D conversion, 8-bit microprocessor [10].

Because ESP8266 module supports TTL serial port, if the TTL level of MCU is 3.3V or 5V, this module can be used. After firmware burning, the module can support three connection modes to realize data transmission, which are: serial port to WIFI STA mode, serial port to AP mode, serial port to STA+AP mode [11].

This part is mainly used for the display of the intelligent agricultural greenhouse system. It can refresh the information of temperature, humidity and light intensity in real time under normal circumstances, display the normal operation of the camera module during the capture, capture the picture and keep the latest capture on the screen.

TFTLCD screen is different from the simple matrix of passive TNLCD and STNLCD. Each pixel of TFTLCD corresponds to a thin film transistor. Therefore, the crosstalk of TFTLCD screen can be eliminated, and the static characteristics of the LCD screen can be independent of the number of scan lines, which greatly improves the image quality of the display.

This module is mainly used to store images taken. Considering to support SPI/SDIO driver, and large storage capacity, THE selection of SD card, and its MCU system used to do external memory is very convenient. Use the development board PC8, PC9, PC10, PC11, PC12, PD2 pins [12–13].

The SDIO interface has the advantage of being compatible with various memory cards. The SDIO controller of STM32F4 consists of SDIO adapter module and APB2 bus interface connecting CPU. The block diagram of its functional parts is shown in Figure 3. In general, SDIO_D0 is used for data transfer, and after initialization the host can be used to change the width of the data bus. If the memory card of multimedia type is connected to the bus, SDIO_D0, SDIO_D[3:0] or SDIO_DO, SDIO_D[7:0] can be used for data transmission. If the SD card is connected to the bus, the host is configured with SDIO_D0/SDIO_D[3:0] for data transmission. If you initialize, SDIO_CMD needs to be set to open mode; For command transfer, SDIO_CMD needs to be set to push-pull mode.

Figure 3

The light source module automatically adds light intensity according to the change of light intensity, and is connected with the PA2 pin of the development board for multiplexing function. Multiplexing is the output comparison function of timer 9 to control the intensity of light source. [14] This part of external circuit is composed of light-emitting diode in series with a pull-up resistor, and its circuit diagram is shown in Fig. 4.

Figure 4

The alarm module mainly uses STM32 to control the buzzer to send sound alarm and WiFi module to send alarm signal to the server. For details about how to send alarm signals, see 3.2.1ESP8266. The buzzer alarm is also relatively simple. It is connected to the PF8 pin of the development board for general output function, and its schematic diagram is shown in Figure 5.

Figure 5

Write the temperature and humidity collection code dht11.c according to the working time sequence diagram of DHT11 temperature and humidity sensor. DHT11_Rst() is used to reset the DHT11, DHT11_Check() is used to wait for the DHT11 response, and DHT11_Read_Data() is used to read the temperature and humidity data. In addition, it is also important to initialize the PG9 pin to pull up, normal output mode.

Lsens.c and adc3.c files are written according to the working principle of photosensitive sensor to complete the acquisition of light intensity. [15] Since ADC channel is used here to obtain the analog value, the configuration function of ADC initialization is first written, and the function of AD converter Adc3_Init() is turned on. Then write the Get_Adc3() function to obtain the value of the seventh channel of ADC3, then initialize the photosensitive sensor to set PA7 as the analog input function, and write Lsens_Get_Val() to complete the acquisition of light intensity value.

After writing functional functions, we can call DHT11_Read_Data() and Lsens_Get_Val() to complete the collection of temperature, humidity and light intensity.

Temperature and humidity light intensity display will mainly use TFTLCD screen, here need to write the screen driver and Chinese characters display function.lcd.c is used to drive the screen and text.c is used to display Chinese characters.

First, write lcd.c according to LCD usage flow chart (Fig. 6). Initialize the required pins to drive the FSMC interface, initialize the LCD screen by using the initialization series in the screen's data manual, and finally set the coordinates and write GRAM to display characters or numbers.

Figure 6

Text.c is written to make it easier to display text content, Get_HzMat() is used to find a font from a font library, Show_Font() is used to display characters of a specified size, and Show_Str() is used to display a string.

At the same time, in order to update the temperature and humidity and light intensity in real time without interfering the operation of the main program, timer 4 is started in this design, and TIM4_Int_Init() is written to initialize timer 4 and enable the NVIC interruption of timer 4.

Write timer 4 interrupt service program TIM4_IRQHandler() to obtain real-time temperature and humidity, light intensity information in real time and display it on LCD screen.

Show_Str() and LCD_ShowNum() are used to display the temperature, humidity, and light intensity. Their code in the program is as follows:

Show_Str(30,90,400,24,"LSENS_VAL:",24,0);

Transmission is the key and difficult point in this design. In this part, esp8266. c is mainly written to establish the connection, usart.c is used to send data through the serial port. In short, this part is to control WiFi module to send and receive data through TCP/IP protocol in wireless local area network through AT instruction set.

In common AT instruction sets, "AT+WAMODE=Y" indicates setting the working mode of WiFi module. At present, there are three working modes of WiFi module, which are as follows: Y equals 1 indicates that the module is in STA mode, and the function of the module is to connect to the wireless network as a wireless WiFi STA. Y = 2 means that the WiFi module is set in AP mode. At this time, the module can act as a WiFi hot spot and allow other WiFi to connect to the module. Y = 3 means that the WiFi module is set to STA+AP mode. At this time, the WIFI module has two functions at the same time. It can be used as a hot spot for the connection of other WiFi devices, and can also be added to other WiFi hot spots. One pattern corresponds to three sub-patterns. This design uses STA mode in which the module connects to other WiFi hot spots. Next, the three modes under STA are introduced in detail, and the sub-modes of the other two modes are similar. The WiFi module can be set as TCP server, TCP client and UDP in STA mode, and the corresponding upper computer is set as TCP client, TCP server and UDP respectively. In this design, WiFi module in STA mode is used as TCP client and configured as TCP server in the upper computer software. Table 4.1 shows the configuration in TCP client mode.

After mastering the AT instruction, it is necessary to write the WiFi module function, write esp8266_start_trans () to connect the hot spot and establish the connection with the server software of the upper computer, send data to the upper computer using esp8266_send_data (), Exit transparent transmission and close the connection with the server through the esp8266_quit_trans() function after the data is sent.

As the serial port to WiFi module is used, the process of data transmission is that MCU sends data to serial port 3, and then serial port 3 receives data and sends it to the upper computer server through WiFi module.

The function of using serial port 3 also needs to be configured. Write usart3_init() with the corresponding pin initialization and NVIC interrupt Settings.

To ensure that the transmission is not disturbed, the NVIC interrupt here should be set to have a high preemption priority. To ensure the correctness of received data, the serial port needs to invoke timer 7 to initialize the serial port, and use the timer 7 interrupt service function to clear data before receiving. Set the interrupt service function USART3_IRQHandler() to receive data after serial port 3 is initialized. Write the u3_printf() function to send data, which is used in writing the esp8266.c data send function, or to send data directly after the ESP8266 module has established a connection to the server.

This part of the function is mainly realized by writing dt.c. The PA3 pin is first configured to initialize it, and the PA3 pin is set to normal input and drop-down mode. Through PA3 pin to infrared detection module output level detection, detection of rising edge trigger interrupt. External interrupts are implemented on interrupt line 3 and need to be configured for interrupt initialization. Configuration interrupt initialization includes initializing PA3, enabling interrupt clock configuration interrupt, connecting PA3 pins to interrupt line 3, and configuring NVIC interrupts for interrupt line 3 and interrupt line 3.

This part of the software is designed to capture and store images. malloc.c is the memory management driver code. The FATFS file system code is open source and only needs to be ported for use on the development board. sdio_sdcard.c is the code for storing data to an SD card. sccb.c, ov2640.c, and photo.c are used to capture JPG images. dcmi.c is used to transfer captured image data to SD card. The process flow chart of capturing process is shown in Figure 7.

Figure 7

To accomplish this function, the driver code of SCCB interface should be written first. The second step is to write the OV2640.c code to turn on the OV2640 module. The OV2640 uses OV_SCL and OV_SDA to configure registers, as well as signals such as OV_PWDN and OV_RESET. Configure OV2640 initialization as shown in Figure 8. Another important function here is to set the image output window function OV2640_Window_Set(), set the image output size function OV2640_OutSize_Set(), set the window function OV2640_ImageWin_Set(), set the image resolution size function OV2640_ImageSize_Set ().

Figure 8

The third step is to compile dcmi.c which mainly completes four functions. The first is to enable the clock, configure the mode of the required pins and set the reuse function. Then complete the configuration of the DCMI. In this step, important parameters such as HSPOL/PCKPOL/VSPOL data width in the DCMI_CR register need to be configured. When frame interrupt is enabled, DCMI interrupt service function is written for data processing.

In the program prepared pwm.c to control the intensity of the light source to achieve this function. Initialize timer 9PWM, define the structure variable required by timer 9, enable TIM9 clock and port A clock, reuse PA2 pin to timer 9, initialize PA2 pin, and then initialize timer 9, because the PWM mode of timer 9 channel 1 is used here, Therefore, it is very important to initialize the channel. Finally, enable timer 9 to complete the setting of timer 9PWM wave.

Then we set the comparison value of PWM wave according to the obtained light intensity value, so as to modify the duty cycle to achieve the purpose of adjusting the light source. The larger the intensity value, the smaller the comparison value and the weaker the light source. This process is shown in Table 2.