EFM32 smart door lock application case

Overview

Smart door locks Refers to locks that are different from traditional mechanical locks and are more intelligent in terms of user identification, security, and management. They are the executive components of the door lock in the smart access control system. The common smart locks currently in use can be classified according to their user identification technology:

Biometrics, including fingerprint locks and iris recognition access control. This type of lock uses the uniqueness of biological features and adopts biometric 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 has a relatively high equipment cost.

· Contactless type, including magnetic card and radio frequency card. It has the advantages of high security, plastic material, convenient configuration and low price.

· Contact type, including TM card, contact IC card\CPU card. High security, stainless steel material, extremely convenient to carry, low price.

Different from traditional mechanical door locks, smart door locks mainly consist of five parts: lock core, main control circuit board, interactive operation panel, handle, and power supply battery box. It is usually an active device that needs to use power to drive the motor to control the actuator in the lock. At the same time, during the installation of the door lock, due to the inconvenience of power wiring and the trouble of disassembly and assembly of battery power supply, smart door locks have strict requirements on the power consumption of the entire device under battery power supply. The power consumption of the whole machine directly affects the battery working life of the smart lock, so it is also an obvious sign of product differentiation of smart door lock manufacturers, and 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 of Norway using the ARM Cortex-M3 core. It has outstanding low-power characteristics and is suitable for "three meters" (electricity meter, water/heat meter, gas meter), industrial control, alarm security system, health and sports application system, handheld medical equipment and smart home control.

EFM32 can be applied to three types of intelligent door lock systems: fingerprint lock, contactless card door lock, and contact card door lock. The system mainly includes power supply battery, identification module (including fingerprint recognition, contactless card reader, contact card reader), control actuator, interactive interface and communication module.

Main control MCU EFM32TG/G

Different models of EFM32 chips can be configured as the main control MCU according to the functional requirements of the smart door lock application. EFM32 chips have good compatibility, and the pins of the same series of chips are pin-pin compatible. In low-end smart door lock applications, the system has relatively low requirements for the Flash and RAM resources of the MCU. EFM32TG222 can be selected as the main control. Its package is QFP48, and the Flash and RAM resources range from 2~4KB and 8~32KB; in high-end smart door lock applications, the system functions are complex, and the requirements for the Flash and RAM resources of the MCU are increased. EFM32G222 can be selected as the main control, and its Flash and RAM resources range from 8~16KB and 32~128KB.

Identification module

The identification module in the fingerprint lock consists of a fingerprint acquisition module and a DSP. The fingerprint acquisition part mainly transmits the fingerprint details to the DSP in the form of a monochrome image, and the DSP executes the algorithm for extracting feature values ​​and compares the feature values ​​with the information in the database, and then transmits the pairing results to the main control MCU via UART.

The identification module of the contactless card door lock is mainly composed of a card reader module and an antenna. When the user's door opening card is close to the door lock, the card obtains energy from the electromagnetic wave generated by the door lock oscillation, and feedbacks the identification request, and then exchanges information through the contactless protocol to determine whether the database in the Flash matches the current request information. This part of the function is mainly implemented in the MCU, and the information communication between the card reader module and the MCU is mainly realized through the SPI interface.

The contact card door lock mainly consists of the contact card slot. The USART in the EFM32 chip has a standard smart card interface (SmartCard, ISO7816). Therefore, the underlying design of the system connecting to the contact card communication is relatively simple, and the user only needs to focus on implementing the upper-level software communication protocol.

Power supply

The operating voltage of EFM32 is 1.8~3.8V, and the operating 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 3.3V lithium battery system without adding an LDO chip at the front end. Alternatively, three 1.5V dry batteries can be used for power supply and an LDO chip can be added to step down the voltage to 3.3V. Since the chip has a relatively wide operating voltage, compared with the traditional 2.8~3.6V MCU, it omits the front-end chips such as the boost chip and charge pump.

· Execution components

The internal timer of EFM32 can be parameterized with PWM with dead-zone control and the commonly used single-edge and double-edge PWM, which is very helpful to control the unlocking motor and perform the corresponding action control. At the same time, in order to facilitate the alarm of illegal lock picking and destruction, the corresponding sound and light alarm equipment can be expanded using I/O. In order to expand the user information storage of the door lock system, the SPI interface of EFM32 can be used to expand NorFlash externally.

Interaction and communication

In high-end door lock applications, a friendly human-machine interaction interface is a necessary part. You can choose to use EFM32 series chips with EBI or TFT driver to expand the LCD screen, use UART to expand the GSM module used for remote alarm, and use I/O to expand user interaction buttons.

When using the EBI interface to implement the extended LCD display, you need to use an LCD with an 8080 interface and a driver chip. When using an MCU with an on-chip TFT driver, you can use a standard LCD interface with an RGB565 interface. In a simple door lock system, you can also omit the display LCD, or use the LCD controller on the EFM32 chip to drive the segment code LCD for simple operation instructions. When the door lock is violently damaged or illegally broken into, the main control MCU can send the corresponding AT execution through UART to control the GSM module to notify the user in the form of a text message.

The system structure of the fingerprint lock is shown in the figure below.

The structural diagram of the contactless card door lock system is shown in the figure below.

The structural diagram of the contact card door lock system is shown in the figure below.

Solution Advantages

Compared with the traditional 8-bit and 16-bit MCU-based smart door lock solutions, this solution based on EFM32 has the following advantages:

Low power consumption

EFM32 is the world's lowest power 32-bit microcontroller. It has five power modes. In EM2 mode, where RTC is running, LEUART, LCD controller, and DMA can run, the power consumption current is only 900nA. In shutdown mode Em4, the power consumption current is only 20nA. The excellent MCU low power consumption characteristics will play an extremely critical role in extending the battery life of the door lock. In order to meet the needs of low-power applications, EFM32 has a complete low-power working mechanism and extremely low-power peripherals. Through the combination of PRS and DMA, LEUART can work in sleep mode without kernel intervention. In the kernel sleep mode without kernel intervention, the LCD can keep displaying, and even simple animation display can be achieved.

EFM32 has peripherals with excellent low-power performance: the on-chip 12-bit ADC consumes only 350μA at a rate of 1Msps; the analog comparator only requires 100nA; the LCD drives an 8×36-segment LCD display at only 0.55μA; the full-function LEUART consumes only 150nA at a rate of 9600bps; AES performs 128/256bit AES encryption/decryption in only 54/75 clock cycles.

High integration and high performance

EFM32 is a Cortex-M3 core, and the core's instruction efficiency and code density are higher than those of traditional 8-bit microcontrollers, especially in algorithm processing. For example, the same C language AES algorithm or 3DES algorithm, when running in an MCU with a Cortex-M3 core, is about 4 times more efficient than running on an 8-bit microcontroller, so the MCU has the ability to process and respond to peripheral events faster. In addition, EFM32 integrates resources such as LCD driver, smart card ISO7816 interface, AES hardware module, etc., and the rich integrated peripherals provide a variety of choices for different system applications.

Good scalability

EFM32's TG, G, and GG series have good compatibility, and the chips of the same series are pin-pin compatible, ensuring that users can tailor different functional requirements on a unified hardware platform. Flash resources range from the lowest 4KB to 1024KB, and RAM resources range from 2KB to 128KB.

Summarize

EFM32 has excellent low power consumption characteristics and is very suitable for the application of smart door lock systems with stringent requirements for low power consumption. The EFM32 core adopts the Cortex-M3 design with outstanding computing performance, which greatly shortens the algorithm processing time in smart door lock applications and improves the performance of the system. EFM32 has rich peripherals, which provides conditions for system expansion functions and cost reduction. Therefore, EFM32 is the only choice for low-power smart door lock master MCU.