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Abstract: Introduced realizes the plan based on monolithic integrated circuit’s electronic formula rotational speed odometer, discussed the course counting principle and the rotational speed instruction principle, has given the automobile rotational speed odometer’s concrete electric circuit schematic diagram which designs with monolithic integrated circuit AT89C2051 and the LM1819 driver. Key word: Rotational speed odometer; Air axis table core; LM1819; Driver; Monolithic computer 1 outline The traditional automobile rotational speed odometer’s function has two; first, with indicator instruction automobile travel instantaneous vehicle speed; second, records the automobile travel with the mechanical counter the accumulation course. The modern automobile is developing to the high speed direction, along with the vehicle speed enhancement, the tradition speedometer which actuates with the flexible axle receives the unprecedented challenge, this is because of the flexible axle when high speed revolving, as a result of steel wire alternate stresses limit limit, but easy to break, simultaneously, the flexible axle will arrange long will have presented the deformation oversized or the movement sluggish and so on phenomena, moreover, regarding the different vehicle type, the rotational speed odometer’s installment position will also receive the flexible axle length and the bending limit. All these, causes based on the non-contact type tachometer generator’s electronic formula rotational speed odometer to be able the rapidly expand. 2 course accumulations realize the principle What speedometer’s transmission ratio expression is: Speedometer revolution axis (flexible axle) when the automobile goes one kilometer has transferred rotation. Uses the Hall non-contact type tachometer generator based on monolithic integrated circuit’s speedometer. This kind of speedometer revolution axis each extension, the Hall sensor will induce sends out 8 pulses. Now as 1:624 vehicle type goes one kilometer take the transmission ratio for the example automobile, then the Hall sensor sends out the pulse number altogether for 8×624=4992, or, each pulse has represented 1/4992 kilometer course. Treats as the exterior interrupt source input these signal impulse to give the monolithic integrated circuit, causes each pulse to have an interrupt, and carries on the counting through the interrupt service to each pulse, like this, when counts 4992 fully, indicated that the automobile went 1 kilometer, then gives the accumulation unit to add again one, coexisting enters the EEPROM unit, finally through the refurbishing LCD liquid-crystal display, then realizes the course tally function. But when programming must pay attention, the MCS-51 series monolithic integrated circuit’s external interrupt has two triggering ways, namely level triggering and border triggering, this design selects the border triggering way, namely uses negative jump to cause the interrupt. The vehicle speed instructed that may use the double coil automobile rotational speed meter, it is composed of the air axis table core and the driving circuit, the air axis table core is usually composed of three parts: The magnet, becomes 90 degrees coils mutually with the revolution axis connected indicator and two. The revolution axis is the table core only movable part, the magnet corner always tends to two coil magnetic intensity vector synthesis direction, the magnetic field strength adds in proportion to the coil the voltage, therefore, through the change voltage’s polarity and the scope, may cause the revolution axis module to rotate theoretically in 0~360 degrees scopes. Obviously, so long as can actuate two coils according to certain rule, may cause the needle deflection position and the input value becomes the linear relationship, namely satisfies the following formula: θ=KVin And Theta is the indicator deflection angle, the unit is; K is the corner constant, the unit is /V; Vin is the input voltage, the unit is V. Each coil’s sum of magnetic intensity vector must follow the deflection angle Theta. Considered the revolution axis module always aims at Hsine and sum of the Hcosine these two orthogonal vectors direction 熢 grasshopper zhuo gives a ride ignorantly wrestles the earthworm to be busy θ=arctan Hsine/Hcosine And may obtain from this: θ=arctan sinθ/cosθ 煹 guarantees the decayed tooth hydra liang wisdom vast place magpie angry string function change obviously by the above formula, but Hcosine according to Theta cosine function change when 熕 obtains the total magnetic field intensity’s direction is the same with Theta the angle direction, because the revolution axis module and the magnetic field strength vector sum’s direction is the same, therefore, the indicator will point at Theta the angle direction throughout. Shown in Figure 1 is the LM1819 driver’s internal composition functional block diagram, it by the electric charge pump, the shaper, the function generator and so on is composed 熓 the sound of flowing water fen Nao fast signal after the internal triode cushion, inputs to the electric charge pump then carries on the F/V frequency voltage to transform, two out-ports according to the input value sine and the cosine function change, 2 feet and 12 foot’s smallest driving force for ±20mA (±4V), the coil may provide the feedback signal public termination to 1 foot for the built-in function generator, simultaneously is the 5.1V zener diode provides the reference voltage. In this electric circuit, K=54°/V, inputs Vin in fact is 4 feet and 8 foot’s potential differences, 8 feet are not only the Norton amplifier’s outputs, is also the function generator input, generally 4 foot’s voltages are 2.1V, therefore has: θ=K (V8-Vref) =54 (V8-2.1) Because V8 is changes in the 2.1V~7.1V scope, therefore LM1819 may actuate the cross meter to cause it to rotate in 0°~270° the scope. 4 electric circuit schematic diagrams Shown in Figure 2 is one kind of automobile rotational speed odometer’s electric circuit schematic diagram. This is a typical monolithic integrated circuit smallest application system. Monolithic integrated circuit AT89C2051 by its low price, the low power loss, the reliability high and easy to program and so on characteristics to be famous, X25045 is a MCS-51 series monolithic integrated circuit electric circuit’s auxiliary chip, mainly takes on the replacement, the voltage examination, the watch-dog and the EEPROM function, this chip’s use enhanced system’s reliability greatly, reduced the periphery chip number, may realize the power failure memory which the course accumulates. LCM1010 is ten type belt back light liquid crystal display module, uses three serial interfaces, it has the power loss to be low and programming convenient characteristic. This demonstration is divided two lines of demonstrations, the first line of 6 demonstration accumulation course, second line of 4 (1 decimal) uses in demonstrating the sub-total course. In the chart K1 is the sub-total course reset key, R4 uses in adjusting liquid-crystal display’s angle of view contrast gradient. Chip X25045 is Xicor Corporation promotes has programmable μP monitor’s CMOS serial EEPROM, has 4096, according to 512×8 organizes. It has 4 bytes pages to write the way and 100,000 use cycles, the data may preserve for 100 years. In order to guarantee the accumulation course unit the units place or sub-total unit decimal place reliable refurbishing, when these unit close limit use cycle, may adopt the form feed the means to cause these data to move to the new unit continues to count. Figure 2 The Hall sensor sends out the signal impulse separable becomes two groups after the reshaping, a group delivers monolithic integrated circuit’s INT1 end to use in accumulating the course counting, another group delivers the LM1819 driver’s rotational speed signal input end (10 feet), then outputs the corresponding sine and the cosine driving signal by the driving circuit according to input signal’s frequency in 2 feet and 12 feet, the magnetic field which the cross coil produces does together uses in the magnet being possible to cause the revolution axis module deflection corresponding angle. But when adjustment must pay attention, the electric capacity C3 size will change the table needle deflection smoothness, C3 is bigger, smoothness will be better, but simultaneously the time sluggish also will enlarge, but C3 too small will cause the table needle vibration; C4 may use in alignment circuit’s linearity and the lag error; The R4 value may change the table needle’s instruction scale division spot. 5 conclusions This design realizes the course by monolithic integrated circuit AT89C2051 to accumulate, the sub-total, the reset and the memory, and actuates the cross coil meter by the LM1819 integrated circuit, thus has realized the vehicle speed instruction. This design proposal cost is inexpensive, the indicator stability is good, the speed of response is quick, the anti-knocking property is strong, the reliability and the performance-to-price ratio are very high. After the actual use proof, this odometer definitely may substitute for the tradition the speedometer which actuates by the flexible axle. Certainly, this is only one kind realizes the plan, may also actuate the cross coil meter by the monolithic integrated circuit through the software, namely controls the meter separately by the monolithic integrated circuit the sine coil and the cosine coil omits the LM1819 integrated circuit. Regarding this, here no longer gives unnecessary detail. |
