EFM32 smart door lock application case

Reprinted from http://www.elecfans.com/analog/20111024225773.html

Overview

Smart locks refer to locks that are more intelligent than traditional mechanical locks in terms of user identification, security, and management. It is the execution part of the locks in the smart access control system. Currently, common smart locks in applications can be classified by user identification technology:

· Biometrics, including fingerprint locks and iris recognition access control. This type of lock uses biometric identification technology to identify user IDs. It has the advantages of high security and no loss or damage, but it is not convenient to configure and is relatively expensive than equipment.

· Non-contact type, including magnetic cards and RF cards. It has the advantages of high security, plastic material, portable configuration, and low price.

· Contact type, including tmcard, contact IC card \ CPU card. High Security, stainless steel material, easy to carry configuration, low price.

Unlike traditional mechanical locks, smart locks mainly consist of five parts: Lock center, main control circuit board, interactive operation panel, handle, and power supply battery box. It is usually an active device and needs to use a power-driven motor to control the execution part in the lock. At the same time, in the installation process of the door lock, due to reasons such as inconvenient power supply and battery power supply, smart door locks have strict requirements on the power consumption of the entire device under the conditions of battery power supply. The power consumption of the entire machine directly affects the battery life of the smart lock tool. Therefore, it is also an obvious indicator of the product differentiation of the smart lock manufacturers. The low power consumption characteristics of the main control MCU are particularly critical in the system.

System Structure

EFM32 is a high-performance, low-power 32-Bit Microcontroller designed by Energymicro, Norway, using the ARM Cortex-M3 kernel. It has outstanding low power consumption characteristics and is suitable for "three tables" (electric meter, water/heat meter, and gas meter) industrial Control, alarm security system, health and motion application system, handheld medical devices, and smart home control.

EFM32 can be applied to fingerprint locks, non-contact snap-in locks, and contact snap-in locks. The system mainly includes power supply battery, recognition module (including fingerprint recognition, non-contact card reading, and contact card reading), control execution mechanism, interactive interface and communication module.

· Main control MCU EFM32TG/G

According to the functional requirements of the smart door lock application, you can configure EFM32 chips of different models as the main control MCU. The EFM32 chip has good compatibility, and the pins of the same series chip are pin-pin compatible. In low-end smart door lock applications, the system has relatively low requirements on MCU Flash and RAM resources. EFM32TG222 can be used as the main control, and QFP48 can be encapsulated as Flash and RAM resources from 2 ~ 4 kb and 8 ~ 32 KB; in high-end smart door lock applications, the system features are complex, and the requirements for MCU Flash and RAM resources are improved. EFM32G222 can be used as the master, and its Flash and RAM resources are from 8 ~ 16 KB and 32 ~ 128KB.

· Recognition module

The fingerprint lock recognition module consists of the fingerprint acquisition module and DSP. The fingerprint acquisition part mainly transmits the fingerprint details to the DSP in the form of a monochrome image. The DSP executes the feature extraction algorithm and compares the feature values with the information in the database, the pairing result is then transmitted to the master MCU through UART.

The non-contact card lock identification module consists of the card reading module and antenna. When a user opens a door card near the door lock, the card obtains energy from the electromagnetic wave generated by the door lock oscillation, and feedback the recognition request. Then, the information is exchanged through the non-contact protocol, to determine whether the database in Flash matches the current request information. This function is mainly implemented in MCU. Information Communication Between card reading module and MCU is mainly implemented through SPI interface.

The contact card lock is mainly in the contact card slot. The usart in the EFM32 chip carries the standard smart card interface (SmartCard, ISO7816 ). Therefore, the underlying design of system connection contact card communication is relatively simple. You only need to focus on implementing the upper-layer software communication protocol.

· Power Supply

The operating voltage of EFM32 is 1.8 ~ 3.8 V, the working voltage range is relatively wide, which is conducive to the simple design of the voltage module. Therefore, the smart door lock can be powered by a V Lithium battery system, without the need to add a front-end regulator chip. Alternatively, you can use three 3.3 V Dry Battery power supplies and the LDC chip to reduce the voltage to V. Because the operating ratio of the chip is wider, compared to the traditional 2.8 ~ 3.6V MCU, which omitting the boost chip, charge pump and other front-end chips.

· Execution part

EFM32's Internal Timer can parameter PWM with Dead Zone Control and commonly used single edge and bilateral edge PWM, which is very helpful for controlling the unlocking motor and executing corresponding action control. In addition, I/O can be used to expand the corresponding audible and visual alarm devices to facilitate alarms for illegal locks and damages. To expand the user information storage of the door lock system, NorFlash can be extended using the EFM32 SPI interface.

· Interaction and communication

In high-end door lock applications, friendly human-computer interaction interfaces are necessary, you can choose to extend the LCD screen with EFM32 series chips with EBI or TFT drives, GSM modules for remote alarm extension with uart, and buttons for user interaction with I/O Extension.

When you use the EBI interface to display an extended LCD screen, you need to use the 8080 interface with the Driver chip LCD screen. When you use the MCU with the TFT Driver in the chip, you can use the standard LCD interface of the RGB565 interface. In a simple door lock system, you can also omit the display LCD screen, or use the EFM32 LCD controller to drive the block-code LCD screen for simple operation instructions. When the door lock is violently damaged or illegal, the MCU can send the corresponding AT execution through UART, And the GSM module can send a text message to notify the user.

The system structure of the fingerprint lock is shown in:

 

The structure of the non-contact card lock system is shown in:

 

The schematic diagram of the contact card lock system is shown in:

Advantages

Compared with the smart Door Lock solution implemented by the traditional 8-bit and 16-bit single-chip microcomputer, this solution based on EFM32 has the following advantages:

· Low Power Consumption

EFM32 is the world's most low-power 32-Bit Microcontroller. It has five power consumption modes, in RTC running, LEUART, LCD controller, DMA EM2 mode that can run, the power consumption current is only 900nA. In the off mode Em4, the power consumption current is only 20nA. The excellent low power consumption of MCU will play a critical role in extending the battery life of the door lock. To meet the needs of low-power applications, EFM32 has a sound low-power working mechanism and extremely low-power peripherals. Through the combination of PRS and DMA, LEUART can work in a sleep mode without kernel intervention. In kernel sleep mode without kernel intervention, the LCD can maintain the display, or even implement simple animated display.

EFM32 has excellent peripherals with low power consumption performance: the 12-bit ADC on the chip is at A speed of 1 MSPs, and the power consumption current only needs 350 μA; the analog comparator only needs NA; LCD Driver 8*36 LCD display, only 0.55 μA; full-featured LEUART, at BPS rate, power consumption current only NA; 128/256-bit AES encryption/Decryption requires only 54/75 clock cycles.

· High Integration and Performance

EFM32 is the Cortex-M3 kernel, the command efficiency and code density of the kernel is higher than the traditional 8-bit single chip microcomputer, especially in algorithm processing has a relatively large advantage. For example, the same C language AES algorithm or 3DES algorithm, In the Cortex-M3 kernel MCU running, the efficiency is about 4 times higher than the 8-Bit Microcontroller running, therefore, the MCU can process and respond to peripheral events more quickly. In addition, EFM32 is integrated with LCD drivers, ISO7816 Smart Card interfaces, and AES hardware modules. A wide range of integrated peripherals provide diverse options for different system applications.

· Good scalability

Efm32's TG, G, and GG series have good compatibility. The chips of the same series are pin-pin compatible, ensuring that users are on a unified hardware platform, you can crop different functional requirements. Flash resources from the lowest 4 kb ~ KB, Ram resources from 2 kb ~ 128kb.

Summary

Efm32 has excellent low power consumption characteristics and is very suitable for applications of smart door locking systems with demanding low power consumption. The efm32 kernel adopts a Cortex-M3 design with outstanding computing performance, which greatly shortens the algorithm processing time and improves the system performance. Efm32 has a wide range of peripherals, providing the system expansion function and cost reduction conditions. Therefore, efm32 is the best choice for Low-Power smart door lock control MCU.