In the past two decades, automobiles have evolved from basic transportation machinery that may be equipped with radios, tape warehouses, and CD players to today's mature and comprehensive mobile information and entertainment platforms. Today’s cars are feature-rich, equipped with a variety of radio technologies that can obtain entertainment information from outside the vehicle (or even from inside the vehicle using a Bluetooth-connected smartphone), can provide positioning information through embedded GPS technology, and can also provide Keyless entry/start system, wireless diagnostic data reading and wireless tire pressure sensor. In addition, many cars today are equipped with embedded cellular radio technology and radar systems for calling for help to enhance driver perception and reduce casualties caused by collisions. In the near future, we will see more wireless functions in cars, such as communication functions between vehicles that help ease traffic and further reduce accidents.
Monitor tire pressure
This article focuses on the role of wireless technology in vehicle safety and security. Let's start with the tire rubber contacting the road: starting from the ground using wireless technology. The wireless pressure sensor in the tire will allow the driver to ensure that the tire pressure remains at the factory recommended level, ensuring safety and optimizing tire wear. The basic tire pressure monitoring system (TPMS) includes one or more TPM sensors, some conditioning/preprocessing circuits, a simple RF transmitter, and a low-cost, low-power microcontroller (Figure 1). On the receiving side, a low-power receiver will capture the data stream, decode and format the data by the microcontroller, and then send it to the CAN/LIN network inside the vehicle or directly send the data to the display.
Figure 1: The wireless tire pressure measurement system combines the inputs of multiple sensors (pressure, temperature, radial acceleration, and tangential acceleration), and sends the preprocessed results to the receiver on the vehicle dashboard via a wireless link.
Tire Pressure Monitoring System (TPMS) is a new standard for improving vehicle safety. Freescale uses its innovative integrated technology to launch a TPMS solution that can monitor tire pressure in real time and alert drivers when tires are not inflated. Freescale TPMS products are designed in accordance with the US Federal Motor Vehicle Safety Standard (FMVSS) 138 and the requirements of global automobile manufacturers.
Freescale's tire pressure monitoring sensor solution uses a single package that integrates a tire pressure sensor, 8-bit microcontroller (MCU), RF transmitter, and a single-axis (Z) or dual-axis (XZ) accelerometer. When the solution is installed in a module on the wheel rim, it can measure the pressure of each tire in real time and send the measurement result to the vehicle dashboard, alerting the driver immediately when the tire pressure is improperly inflated.
The Freescale Xtrinsic smart sensor module integrates pressure, temperature and acceleration sensors, RF transmitters, and microcontrollers in a 7 x 7 mm miniature package. A variety of Freescale processors can be used as low-power microcontrollers in this module, depending on the number of processing tasks the MCU needs to perform.
For example, Freescale's MC12311 is a system-in-package (SiP) device based on the 8-bit HCS08 series of MCUs, and the company's MKW0x device is a 32-bit MCU based on the ARM Cortex-M0+ CPU core. Both MC12311 and MKW0x series devices have integrated RF transmitters below 1 GHz in the chip.
Let's take a look at the MKW01Z128CHN device in the MKW0x series, which is a highly integrated cost-effective, smart radio, wireless node solution within 1 GHz. In addition to the two-way radio below 1 Ghz, the MKW01 series also embeds a large number of peripherals, and has a wide operating frequency range, covering the 315, 433, 470, 868, 915, 928 and 960 MHz frequencies. Both MKW01 and MC12311 use transceivers capable of FSK, GFSK, MSK or OOK modulation. These configurations allow users to minimize the number of external components. (An alternative is centered on the company's Kinetis EA series of devices, but requires an external RF transmitter.)
Figure 2: Freescale Semiconductor's highly integrated MKW0x microcontroller series is aimed at low-power wireless applications such as tire pressure monitoring, and integrates sub-1 GHz transceivers that can operate in different ISM frequency bands in the range of 315-960 MHz.
Keyless entry
The usual way to enter today's cars is to use an electronic key fob. With this keychain, you can open and lock the door, activate or cancel the alarm, adjust the position of the seat and mirror, and even start the car without inserting the key into the ignition switch. The embedded technology in the smart keychain will generally incorporate a short-range wireless transmitter or transceiver, and a microcontroller that supports the AES encryption algorithm and can generate rolling codes; of course, these circuits should all be of low power consumption. In order to achieve several years of work under the drive of a single button battery.
Atmel is a company that provides a variety of keychain solutions. It has now launched a variety of pure transmitters and a variety of two-way microcontrollers (such as ATA577x, Figure 3) that can be placed inside the keychain, and can be integrated into the car The same number of solutions in the management system. The various pure transmission solutions of the keychain differ only in frequency, which is usually determined by the use area of ​​the keychain in the world. The three frequency bands include 68-928 MHz, 310-350 MHz and 429-439 MHz, and the transmitter module uses ASK or FSK to modulate the signal. The MCU used in the key fob is taken from the company's AVR ATtiny44V 8-bit microcontroller, with a data transfer rate of up to 32 kb/s.
Figure 3: Atmel ATA577x series are highly integrated microcontrollers, which integrate an RF transmitter or a complete transceiver and hardly require any external components. These controllers can reliably output rolling codes for remote key entry and car start.
Microchip is also a provider of keyless remote entry solutions. It has introduced PIC12, PIC16, PIC18, and PIC24 ultra-low power microcontroller series. The first two series are used in conjunction with the KeeLoq algorithm supported by the MCU's internal hardware encryption module. Two series are used in the receiver subsystem (Figure 4). For example, the low-power PIC12F635 8-bit microcontroller consumes only 1 nA in standby with a 2.0 V power supply, and only 100 microamps when it is activated and the clock frequency is 1 MHz.
Figure 4: Two-way transponder system for passive keyless entry system. The system uses low-frequency commands and intercom channels, and the keyed data is sent by the transponder to the base station through the UHF RF channel.
KeeLoq is a non-linear algorithm that can create an independent launch task every time a button is pressed. This function invalidates various code capture and resend methods. To achieve UHF communication between the key fob and the receiver module, the transmitter solution allows system designers to use frequency shift keying (FSK) or amplitude shift keying (ASK) modulation methods to generate transmission tasks. In addition, it also provides corresponding receiver solutions for filtering and decrypting wireless data transmission tasks.
Suppliers of low-power MCUs for key fobs and other low-power applications also include STMicroelectronics and Texas Instruments.
Among the many well-known wireless applications for vehicles, the tire pressure measurement and key fobs listed in this article are just the tip of the iceberg. At present, there is still a lot of work to be done to define various standards, so as to enable communication between vehicles, between vehicles and "smart" roads, and realize solutions such as autonomous vehicle driving and inter-vehicle collision avoidance communication.
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