The traditional mechanical speedometer outputs power from the wheels, and the worm drive shaft drives the tip of the flexible shaft to rotate synchronously, so that the permanent magnets of the fixed and flexible shafts on the other side also rotate synchronously, thus generating a rotating magnetic field, which acts on the rotating disk, which accelerates the rotation of the disk and deflects the pointer together with the watch. When the electromagnetic torque generated by the spring and the resistance torque are balanced, the indicator is kept at a deflection angle. Pointer deflection is proportional to angle and speed, so its speed can be used.
The mechanical defects of speedometer are obvious. Because the deflection of the dial indicator shaft is directly proportional to the degree of rotation, the generated magnetic force is smaller when the rotating speed is lower, and fluctuates more with the change of rotating speed. Therefore, when the pointer of the low-speed meter swings violently, the measurement and display accuracy is not high. For a car with a rear engine, the deflection of the speedometer pointer is the power transmitted by a flexible shaft (such as a cab), and the arrangement of a long flexible shaft is inevitable. It is definitely a very difficult thing to arrange such a long flexible shaft properly in structure. In addition, the traditional mechanical speedometer has all the defects, and this instrument has been gradually eliminated.
This paper introduces the design of speedometer based on minimum single chip microcomputer system and Hall sensor. Different speed sensors input pulse signals with different frequencies into the single chip microcomputer for control and calculation, and then display them with LED module, so that the mileage data and speed of electric bicycles can be displayed intuitively to users.
The system consists of Hall sensor, RC filter circuit, single chip microcomputer AT89S8252, system LED display module and data storage circuit. Hall sensor includes signal amplification and waveform shaping. The purpose of amplifying the test signal is to reduce the amplitude required for signal measurement; The waveform transformation and waveform shaping circuit is used to transform the amplified signal, which can be connected with the TTL signal of single chip microcomputer; The internal timer T 1 control pulse of input pin T0 can be set by single chip microcomputer, so that the number of pulses detected in unit time when pin T0 is added can be accurately calculated. The design of vehicle speed display adopts LED module, and the mileage is converted by I2C bus, and stored by E2PROM, which not only saves the required MCU port line and peripheral equipment, but also simplifies the software programming of the display part.
Firstly, this paper expounds the design of equipment details necessary for designing odometer; In the second half, the design and implementation of software and hardware are analyzed carefully. Then the system modeling process and the corresponding system model are given, and the control simulation is carried out on this basis, and the simulation results are compared.
The odometer has simple design structure, low cost and obvious advantages of stability and reliability. And it can be extended to include the function of table speed, which is more convenient to understand your current situation.
Key words: single chip microcomputer, LED digital tube, Hall sensor, EEPROM memory.