An embedded automobile digital instrument circuit design

Car Audio Crystal 3.2*2.5mm 3225 24M (24.000MHZ) 20PF 10PPM 20PPM 30PPM

One-piece inductor

Automobile instrumentation is an information exchange interface between the driver and the car, and plays an important role in car safety and economic driving. In recent years, with the development of automotive electronic technology, the display information of automobile meters has also been increasing, and the traditional mechanical pointer type automobile combination meters cannot meet the needs of current use. In particular, computers, microelectronics and various fieldbus communication technologies are widely used. Intelligent digital instruments with embedded microprocessors as the core will be an inevitable trend in the development of automotive instruments. This paper presents an embedded automotive digital instrument design.

Power and reset circuit design

The automotive digital instrumentation system is powered by a car battery. The voltage of the car battery is about 12 V. The system requires 5 V, 2.5 V and 3.3 V operating voltage. The S3C44BOX core operating voltage is 2.5 V. The operating voltage of the I/O port. It is 3.3 V, and the conditioning circuit and some driver devices require a working voltage of 5 V. Therefore, the system uses the 7805 regulator as the 5 V voltage converter, and uses AS2515AU2.5 and AS2515AU3.3 as the 2.5 V and 3.3 V voltage converters respectively. Mileage information can be stored in time when power is off, and a 1 000 μF capacitor is required for the power ground. When power is off, the large capacitor can ensure that the S3C44BOX works for a period of time and completes the storage of mileage information. The reset circuit uses a dedicated reset circuit IPM811 to achieve stable startup of the system. Figure 2 shows the system power circuit.

Processing circuit design for vehicle speed, water temperature, oil quantity and switching quantity

Since most of the cars work in harsh environments, they will interfere with the vehicle speed sensor signal. Therefore, the vehicle speed pulse signal needs to be processed before input to the interrupt port EINT0. Here, the RC filter, the triode amplification and the Schmitt shaping method are used to adjust the vehicle speed pulse signal. The vehicle speed pulse conditioning circuit is shown in Figure 3.

The water temperature and oil quantity signals are resistance signals, which must be converted into voltage signals, and then their voltage signals are input to the AD port of the S3C44BOX. The other switches are filtered and stepped down to the I/O port of the S3C44BOX.

CAN bus communication circuit design

S3C44BOX has no SPI interface, but has SIO interface. The SIO module can transmit and receive data bits on the rising edge or latch the data bit on the falling edge. Therefore, it can be increased by setting the register corresponding to the SIO module of S3C44BOX. Along the transmit data, the falling edge receives the data, which matches the SPI bus timing of the MCP2510. The CAN bus communication circuit is shown in Figure 4.

Stepper motor head circuit, etc. Among them, the stepping motor adopts Sititec's special stepping motor X15.168 for automobile instrument and X12.017 for special four-channel stepping motor. The I/O level of the S3C44BOX is 3.3LVCMOS level, while the X12.017 is a 5V CMOS level, which requires 74LVX4245 level shifting.

Using S3C44BOX and embedded real-time operating system μC/OS_II, a high-precision, high-sensitivity, stable and stable embedded bus digital instrument is designed. S3C44BOX is rich in resources and fast in execution. It can expand many functions, such as IC card, GPS, black box, etc. In addition, the embedded real-time operating system simplifies the application and can call system tasks efficiently and in real time. Therefore, the digital instrument system of this car can be very A good solution to the problem of automotive instrumentation towards comprehensive informationization.