China's existing garbage charging standards are low, and the government has to invest a large part of the funds every year to supplement the garbage disposal enterprises. After the reform of the garbage charging system, it can not only make up for government and enterprise investment, but also urge residents to strengthen the awareness of waste reduction and resource utilization, and promote waste reduction, resource utilization and harmlessness.
Many developed countries have implemented garbage metering charges. The experience of Japan, South Korea and the United States is based on the calculation of garbage bags. The residents spend more money when they throw more garbage and buy more bags. The other form is to charge directly according to the weight of garbage. Barrel garbage costs a certain amount of money, and can avoid the "one size fits all" approach to household or per capita charges.
This paper designs a garbage weighing and billing control system based on single chip microcomputer. Compared with other control systems, the single-chip microcomputer system has the advantages of small size and low cost.
1 system requirements and selection of the main controller
The working principle of the system is as follows: The garbage bin is composed of three different boxes, which collect garbage (box 1), recyclable garbage (box 2) such as paper and plastic, and other non-recyclable garbage (box 3). Install a properly sized input door on the top of each cabinet and a weighing platform at the bottom. When the household is ready to put garbage, take out the recharge card. When the balance in the card is sufficient, you can open the box 1, box 2 or box 3 to carry out the garbage. The box 1 and the box 3 are reduced according to the weighing, and the box 2 is charged according to the weighing. In order to prevent different types of garbage from being mistaken, the input doors of each box can be made different. For example, the paper input box control door should be made into a flat mouth, and only paper or newspapers and magazines can be put into operation. The hardware structure of the control system is shown in Figure 1.
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Compared with other controllers, the single-chip microcomputer has the advantages of small size, low price and high cost performance. Therefore, the control system selects the AT89 S51 single-chip microcomputer which is currently the most widely used as the main controller, and can conveniently communicate with the radio frequency circuit, display circuit and communication circuit. The A/D conversion circuit interface is connected to form a complete control system.
2 IC card and card reader circuit
The non-contact IC card, also known as the RF card, solves the problem of passive and contactless compared with the contact IC card, and has the advantages of high reliability and convenient operation. In this design, the currently popular Mifare1 card and controller are selected. The antenna coil connected to the dedicated card reader chip continuously emits a set of electromagnetic waves with a fixed frequency of 13.56 MHz. When the Mifare1 card is close, the LC series resonant circuit in the card resonates, causing the capacitor to charge to generate electric charge. When the capacitor is charged to 2 V. When the capacitor acts as a power source to provide operating voltage for the circuit on the card, the data in the card is transmitted or received and stored in the controller [1].
MFRC500 is a non-contact communication high-integration card reader chip for 13.56 MHz. It integrates all types of passive contactless communication methods and protocols at 13.56 MHz. It supports Mifare1 card. The interface circuit with AT89S51 is shown in Figure 2. According to the system requirements, the functions required by the corresponding part of the control program are as follows [2]:
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(1) When there is no card swiping, the system is in a waiting state; when there is a swipe card, the information in the card is identified, including the user information, the balance in the card, and the storage area inside the system, and the display program is called.
(2) The payment method can be optional for recharge and billing. This design uses a recharge method to deduct food waste and non-recyclable waste, while paper and plastic waste can be recharged into the card.
3 Design of weighing module and display module
(1) Selection of load cell
For electronic scales, platform scales, etc., aluminum alloy cantilever beam sensors are suitable for deformation caused by bending. Strain gauges are attached to the upper and lower sides of the area where the curved surfaces are concentrated to form a full bridge measurement circuit. Figure 3 shows the CYT-204 series cantilever beam load cell with a range of 0~0.1 T, high precision and low drift. The output is 0~5 V, which is easy to interface with the microcontroller. The size is 130 mm × 32 mm × 32 mm. Easy to install [3].
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(2) Design of A/D conversion circuit and display circuit
The TLC2543 is TI's 12-bit serial analog-to-digital converter that uses a switched capacitor successive approximation technique to perform the A/D conversion process. The serial input structure can save the I/O resources of the single-chip microcomputer, and has the characteristics of simple interface, moderate price and high resolution. It has a wide range of applications in instrumentation. Therefore, TLC2543 is used for A/D conversion in this system. element.
The display devices commonly used in control systems include LED displays and LCD displays. In addition to displaying digital characters, LCDs can display characters. Therefore, this design uses the currently very popular LCD1602 display module for display of weighing results.
The display control program implements display of user information, including name, house number, and card balance. When the user presses the box selection button, the garbage weight metering device opens the corresponding input door. After the user delivers the garbage, the card balance can be increased or deducted and displayed according to the type and weight of the garbage.
4 Design of storage module and communication module
AT24C08 is ATMEL's EEPROM memory. Its wiring is very simple. It only needs 2 signal lines. Its storage capacity is 1 KB. One memory module can store hundreds of user information. The interface circuit with MCU is shown in Figure 4. Show.
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Statistics on the garbage discharge of each household need to be read out from the household garbage disposal information stored in the system. The serial communication interface of the single chip microcomputer can be extended to the USB interface, the RS232 interface and the GPRS interface. There is only one serial interface of AT89S51 in this system. Considering the convenience of the system, USB port expansion is adopted in this design.
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