A simple design of smart refrigerator

Automatically monitoring the freshness of food and giving an alarm in time greatly facilitates people to manage food in the refrigerator. People often eat or discard food when they are not sure whether it is expired. The former may be harmful to health, while the latter wastes food. Using a smart refrigerator can quickly solve such problems. In addition, as a self-developed product, we should strive to occupy the corresponding market as soon as possible to gain the initiative in development.

1 Preliminary preparations

According to the functions of current refrigerators and the needs of consumers, the design goal is a smart refrigerator that can detect food quality. Before designing, it is necessary to analyze the consumer market to position the refrigerator price and improve the functions. Of course, this refrigerator is not designed for people who need a high-quality life. The general public with regular life and stable income are also our consumers.

1.1 Consumer Market Analysis

In order to facilitate consumers to more conveniently and easily know the shelf life of food during the use of refrigerators, smart refrigerators just meet the needs of consumers. Intelligent products have become a development trend and are gradually becoming popular. According to statistics, the national production capacity of refrigerators (including ordinary refrigerators) is more than 20 million units, while the annual demand for refrigerators in my country is 12 million units. The domestic production capacity is obviously in excess, but my country exports 22.45 million refrigerators each year. Therefore, refrigerators on the market are in short supply. Moreover, in today's world where people attach so much importance to health and the price is comparable, compared with ordinary refrigerators, a smart refrigerator that can detect food quality will be the first choice of consumers. In general, there is a vast market for smart refrigerators.

1.2 Design positioning

According to market research and analysis, my country's refrigerator market is in short supply, and the market for functional smart refrigerators will be even larger. The smart refrigerators we designed that can monitor the shelf life of food are mainly for middle- and high-end people with stable income and life. In terms of price, we will set it at 3,000 to 5,000 yuan, which is the most popular product. In terms of function, the main purpose is to monitor the shelf life of food. Many foods are placed in the refrigerator but their shelf life is ignored, such as fruits, fresh meat, etc. The refrigerator has intelligent functions, which can sort out food information and remind people of food that is about to expire in time, so that people can use safe food and ensure people's health.

2 Refrigerator structure

The internal structure is shown in Figure 1. The working principle of the refrigerator is shown in Figure 2.

Figure 1 Refrigerator internal structure

Figure 2 Refrigerator working principle

The refrigerator is a single-door refrigerator, mainly divided into two layers. The first layer is the freezer, and the freezing temperature can be adjusted by the nearby rotary button. The second layer is the refrigeration layer, which is mainly divided into a meat layer (the space size can be changed), a fruit and vegetable layer (the space size can be changed), and a beverage layer. There is a reminder speaker and a display screen on the side of the refrigerator.

3 Function Implementation

The core function of this smart refrigerator is to monitor the quality of food and manage the food input. This function consists of three core parts: control system, food identification and input management system, and food monitoring and alarm system.

3.1 Control System

3.1.1 Controller selection

In order to integrate the functions of each system, the STC89C51RC embedded microcontroller is used as the control system. As shown in Figure 3. The STC89C51RC microcontroller has the characteristics of small size, strong control ability, high integration, high reliability, and high cost performance, and is widely used in household appliances. The STC89C51RC uses the ISP (In System Programming) in-system programmable chip of the 8051 core, with a maximum operating clock frequency of 80 MHz. The chip contains 4K Bytes of Flash read-only program memory that can be repeatedly erased and written 1,000 times. The device is compatible with the standard MCS-51 instruction system and 80C51 pin structure. The chip integrates a general 8-bit central processor and ISP Flash storage unit. It has the characteristics of in-system programmability (ISP). With the control program on the PC side, the user's program code can be downloaded into the microcontroller, eliminating the need to purchase a general programmer, and the speed is faster.

Figure 3 STC89C51ＲC Figure 4 Keil operation interface

3.1.2 Selection of programming software

The programming software is written using the Keil compiler system, as shown in Figure 4. This system is developed by KEIL and is a highly readable modular system programming software that can easily write, compile and modify programs. To make the microcontroller and various hardware work together, it must be achieved through programming. Using C language compiler software, Keil can use any 51 series microcontroller, and the programming software has a perfect compilation and development environment.

After the program is written, it is necessary to import the program. For the program import software, select STC-ISP to import the program. As shown in Figure 5. STC-ISP is a microcontroller download programming and burning software, which is designed for STC series microcontrollers. It can download STC89 series, 12C2052 series and 12C5410 series STC microcontrollers. It is easy to use and has been widely used.

Figure 5 STC-ISP operation interface

3.2 Food Identification and Entry Management System

The refrigerator uses RFID food management technology. Radio frequency identification (RFID) is a wireless communication technology that can identify specific targets and read and write related data through radio signals without establishing mechanical or optical contact between the identification system and the specific target. Attach RFID electronic tags to the food to be stored to realize the identification of the food electronic ID card. The RFID reader reads, writes and identifies the RFID electronic tags, automatically identifies the category, time and location of the stored food in real time, and manages it. Secondly, there will be a pressure sensor in each layer of the refrigerator. When food is put in, the pressure sensor will transmit the signal to the microcontroller, and the microcontroller will make corresponding processing according to different signals.

3.3 Food Monitoring System

Generally speaking, vegetables cannot be eaten after being stored in the refrigerator for a week, while the freshness period of fruits is generally 3 to 4 days, and that of meat is generally 2 to 3 days. The refrigerator is divided into meat layer and vegetable and fruit layer. When meat or vegetables and fruits are put into the refrigerator, the pressure sensor transmits the signal to the microcontroller, and the microcontroller will make corresponding processing according to different signals.

3.4 Alarm system

The alarm system is mainly composed of a buzzer. The single chip receives signals from different electronic tags and uses the buzzer to alarm. When the monitoring system detects an electronic tag, it counts down according to different electronic tags. After the countdown is completed, the alarm system will use a buzzer to remind the owner that there is a problem with the quality or freshness of the food, and will display the specific location of the food on the LCD screen. The alarm system will not continue to alarm, each alarm lasts for 2 minutes, and there is no alarm at night.

3.5 Functional module programming

The functional module program design flow chart is shown in Figure 6. After identifying fruits, vegetables and meat through RFID, the information is fed back to the microcontroller to enter the food. After entering, the pressure sensor signal is combined to determine the location and time of the food, and an alarm and display prompt are issued within a certain period of time according to the type of food. As shown in Figure 7.

Figure 6 Functional module program design flow chart

Figure 7 LCD display reminder of meat spoilage in practice

The functional module mainly has 5 steps: RFID identification and entry, pressure sensor, microcontroller central processing, buzzer alarm, and LCD display.

4. Advanced product design

This product is a smart refrigerator that can monitor and manage food freshness. Compared with ordinary refrigerators, it has added food freshness monitoring and food entry management functions. It can remind people to eat food that is about to go bad in time, and can accurately display the name and location of the food, making it convenient for people to find food that is about to go bad as soon as possible.

4.1 Advantages of control system

The control system selects STC89C51 single-chip microcomputer as the controller. There are four major advantages in choosing this controller: ① Low cost. Since the price of single-chip microcomputers is relatively low now, and the price of components of peripheral circuits is not high, the overall design has a relatively low cost; ② The external storage capacity can be expanded as needed, and the design can be relatively flexible; ③ Since there are many well-designed subroutines and library files, they can be directly called in the system software design, reducing a large workload; ④ Excellent performance/price ratio. Since the hardware structure of the single-chip microcomputer is simple, the development cycle is short, the control function is strong, and the reliability is high, therefore, under the condition of achieving the same function, the control system developed with a single-chip microcomputer is cheaper than the control system developed with other types of microcomputers.