Ultra-low power wireless parking lot detection system based on MMC3282+EFM32

Overview

With the rapid development of economy and the improvement of people's living standards, the number of cars has increased year by year, but it has also led to the worsening traffic conditions. In order to solve the increasing traffic congestion problem and improve traffic quality and capacity, many intelligent transportation systems have emerged in the current market, including wireless parking lot vacancy detection systems.

The wireless parking lot detection system solution introduced in this document is based on Energymicro's 32-bit Cortex-M3 core ultra-low power microcontroller EFM32 and MEMSIC's highly integrated MMC3282 sensor. It can give full play to the ultra-low power consumption and high computing power of EFM32 and the high-precision measurement capability of MMC3282; it will become the best choice for low-power wireless parking lot detection solutions.

System Framework

The framework of the wireless parking lot detection system is shown in Figure 1. The wireless parking lot detection system includes an ultra-low power microcontroller EFM32TG110F32, a geomagnetic sensor MMC3282, a 2.4G low-power wireless data transmission module, and a system power supply. The system detects geomagnetic signals through geomagnetic sensors to obtain corresponding data, and then the microcontroller analyzes and processes the geomagnetic signal data through corresponding algorithms, and finally realizes data interaction with other systems through the wireless data transmission module. The entire system can be powered by a 3.6V lithium battery; due to the high processing performance of EFM32TG110F32 and various low-power peripherals, combined with the ultra-low-power geomagnetic sensor MMC3282 and the 2.4G low-power wireless data transmission module, the entire system greatly reduces power consumption.

The wireless parking space detection device is part of the wireless intelligent parking lot management. It is installed at a specific location of the parking space. Once a car is parked, the geomagnetic sensor determines the parking and leaving of the vehicle by detecting the changes in the magnetic field of the car. At the same time, the collected data is processed by the MCU and transmitted to the wireless node controller via RF, and then transmitted to the control terminal. In this way, the control terminal can guide and divert vehicles entering the parking lot to find vacant parking spaces more quickly.

Figure 1 Block diagram of wireless parking lot detection solution

Hardware Design

1. Main controller circuit part

The wireless parking lot detection system uses EFM32TG110F32 as the main controller. The controller uses ARM's 32-bit Cortex-M3 core, which has higher processing performance and code density and lower power consumption than traditional 8-bit and 16-bit microcontrollers.

EFM32TG110F32 has 5 low power modes, EM0-EM4. In the low power mode of EM2, the microcontroller still has the communication or control functions of LEUART, LETIMER and LESENSE, and the power consumption is only 900nA. Moreover, it has flexible wake-up methods and an autonomous PRS system, which can be awakened by external I/O, I2C communication interface, LEUART communication signal, etc. The hardware circuit design of the main controller is shown in Figure 2.

Figure 2 Main controller circuit

2. Geomagnetic sensor hardware circuit

MMC3282 is a 3-axis geomagnetic sensor launched by MEMSIC Semiconductor. It integrates the functions of geomagnetic signal detection and geomagnetic signal data processing, and saves the final detection result containing 14 data bits in the corresponding register, and then exchanges data with peripheral devices through the I2C interface; the geomagnetic measurement accuracy range of MMC3282 is ±8 Gauss, and it can detect X, Y, and Z three-axis geomagnetic signals; the sensor adopts an ultra-small LGA (3.0×3.0×1.0mm) package, and its power supply voltage range is 2.5V~3.6V, making it an ultra-low power geomagnetic detection product.

The software and hardware designs of MMC3282 are very simple, and the design of the hardware circuit diagram is shown in Figure 3.

Overview

With the rapid development of economy and the improvement of people's living standards, the number of cars has increased year by year, but it has also led to the worsening traffic conditions. In order to solve the increasing traffic congestion problem and improve traffic quality and capacity, many intelligent transportation systems have emerged in the current market, including wireless parking lot vacancy detection systems.

The wireless parking lot detection system solution introduced in this document is based on Energymicro's 32-bit Cortex-M3 core ultra-low power microcontroller EFM32 and MEMSIC's highly integrated MMC3282 sensor. It can give full play to the ultra-low power consumption and high computing power of EFM32 and the high-precision measurement capability of MMC3282; it will become the best choice for low-power wireless parking lot detection solutions.

System Framework

The framework of the wireless parking lot detection system is shown in Figure 1. The wireless parking lot detection system includes an ultra-low power microcontroller EFM32TG110F32, a geomagnetic sensor MMC3282, a 2.4G low-power wireless data transmission module, and a system power supply. The system detects geomagnetic signals through geomagnetic sensors to obtain corresponding data, and then the microcontroller analyzes and processes the geomagnetic signal data through corresponding algorithms, and finally realizes data interaction with other systems through the wireless data transmission module. The entire system can be powered by a 3.6V lithium battery; due to the high processing performance of EFM32TG110F32 and various low-power peripherals, combined with the ultra-low-power geomagnetic sensor MMC3282 and the 2.4G low-power wireless data transmission module, the entire system greatly reduces power consumption.

The wireless parking space detection device is part of the wireless intelligent parking lot management. It is installed at a specific location of the parking space. Once a car is parked, the geomagnetic sensor determines the parking and leaving of the vehicle by detecting the changes in the magnetic field of the car. At the same time, the collected data is processed by the MCU and transmitted to the wireless node controller via RF, and then transmitted to the control terminal. In this way, the control terminal can guide and divert vehicles entering the parking lot to find vacant parking spaces more quickly.

Figure 1 Block diagram of wireless parking lot detection solution

Hardware Design

1. Main controller circuit part

The wireless parking lot detection system uses EFM32TG110F32 as the main controller. The controller uses ARM's 32-bit Cortex-M3 core, which has higher processing performance and code density and lower power consumption than traditional 8-bit and 16-bit microcontrollers.

EFM32TG110F32 has 5 low power modes, EM0-EM4. In the low power mode of EM2, the microcontroller still has the communication or control functions of LEUART, LETIMER and LESENSE, and the power consumption is only 900nA. Moreover, it has flexible wake-up methods and an autonomous PRS system, which can be awakened by external I/O, I2C communication interface, LEUART communication signal, etc. The hardware circuit design of the main controller is shown in Figure 2.

Figure 2 Main controller circuit

2. Geomagnetic sensor hardware circuit

MMC3282 is a 3-axis geomagnetic sensor launched by MEMSIC Semiconductor. It integrates the functions of geomagnetic signal detection and geomagnetic signal data processing, and saves the final detection result containing 14 data bits in the corresponding register, and then exchanges data with peripheral devices through the I2C interface; the geomagnetic measurement accuracy range of MMC3282 is ±8 Gauss, and it can detect X, Y, and Z three-axis geomagnetic signals; the sensor adopts an ultra-small LGA (3.0×3.0×1.0mm) package, and its power supply voltage range is 2.5V~3.6V, making it an ultra-low power geomagnetic detection product.

The software and hardware designs of MMC3282 are very simple, and the design of the hardware circuit diagram is shown in Figure 3.

Figure 3 MMC3282 hardware circuit diagram

2. Wireless communication module circuit

The wireless transmission module uses Huaotong's HAC-LBee/S low-power wireless data transmission module. HAC-LBee/S is a low-power wireless data transmission module using the 802.15.4 protocol stack. Its transmission power is 100mW (20dBm), and its receiving sensitivity is -105dBm (BER=10-2). HAC-LBee/S uses an open frequency band, and does not require frequency application. The carrier frequency is 2.4GHz, and it has high anti-interference ability and low bit error rate; HAC-LBee/S has an air transmission rate of up to 250kbps, and in line-of-sight conditions, the reliable transmission distance can reach 1000m. Its receiving current is ≤50mA, and its transmitting current is ≤160mA. It is small in size and light in weight. It uses a single-chip RF and MCU integrated circuit, and requires fewer peripheral circuits, high reliability, and low failure rate. Its hardware circuit is shown in Figure 4.

In Figure 4, ZXM61P03 is used as a switch tube. When PD7 is at a high level, the power supply pin of the wireless data transmission module is equivalent to a circuit breaker, which can more effectively reduce the power consumption of the system.

Figure 4 Wireless transmission module circuit

4. System power supply

The entire system can be powered by an external power supply through the Power port, or it can be powered directly by the 3.6V battery on the board. The circuit diagram is shown in Figure 5.

Figure 5 System power circuit

Software Design

The software of the wireless parking lot detection system can be divided into three parts: UART communication between the microcontroller and the wireless data transmission module, I2C communication between the microcontroller and the geomagnetic sensor module, and the algorithm for analyzing geomagnetic data.

The LEUART of the microcontroller EFM32TG110F32 can work in the EM2 low-power mode. It uses a 32.768KHz clock and a maximum communication baud rate of 9600baud/s. Through the cooperation between LEUART and DMA, the entire system can greatly reduce power consumption.

The geomagnetic sensor module uses the I2C communication interface. The device address of MMC3282 is 0x6x. After the main controller addresses the sensor through the device address, it measures the data by operating the sensor's internal control register 0, and can read the measurement results from the 6 data registers inside the sensor. After reading the geomagnetic data collected by the sensor, the main controller analyzes the geomagnetic data through the corresponding algorithm and can send the final results to other devices through the wireless data transmission module.

In order to control power consumption, the system can turn off the power of the wireless transmission module through the corresponding pin when there is no data transmission, thereby more effectively reducing the power consumption of the entire system.

Solution Advantages

The advantages of the wireless parking lot detection system based on EFM32TG110F32 and MMC3282 include:

1. Compared with traditional 8-bit and 16-bit MCUs, EFM32TG110F32 uses Cortex-M3 as its core, which has stronger computing and processing capabilities, thus improving the performance of the entire system;

2. Both EFM32TG110F32 and MMC3282 have the advantage of low power consumption, which makes the power consumption of the whole system lower, increases the battery life of the system, and indirectly reduces the battery cost of the whole system;

3. EFM32TG110F32 integrates low-power functional modules such as DMA, LEUART and I2C. At the same time, its Flash can be used for data storage, which reduces the peripheral components of the overall solution and reduces the solution cost.

Summarize

To summarize the above, the wireless parking lot detection system designed with EFM32TG110F32 as the main MCU and MMC3282 as the key detection components fully utilizes the high performance, low power consumption and good integration of EFM32TG110F32. At the same time, combined with the advantages of easy development, high integration and low power consumption of MMC3282, it will become the best choice for wireless parking lot detection.