Firstly, the classification of engine tachometer is briefly introduced. Secondly, the circuit of digital engine tachometer is analyzed. On the basis of briefly introducing the main components of the circuit, the structure and working principle of the circuit components: display control circuit, pulse signal counting circuit, display circuit and power supply circuit are preliminarily analyzed. Finally, the circuit diagram of the whole circuit is given.
1 preface
Engine tachometer has many forms, and its main classification is shown in table 1 [1]. Figure 1 is the circuit diagram of digital indicating engine tachometer given in reference [2]. The structure and working principle of this circuit are briefly analyzed below.
Table 1: classification of engine tachometer
Figure 1: Circuit diagram of digital indicator tachometer
2 component introduction
MCT MOS controlled thyristor (MOS controlled thyristor)
MCT is a power device, which is mainly used for power switching because of its high input impedance, fast switching speed, high voltage and large current. MCT2 is produced by Dezhou Company, and its equivalent circuit consists of light emitting diode and phototransistor (see circuit diagram). The input-output voltage difference can reach 1.5KV, and the forward input current can reach 60mA constant current with a peak value of 3A[ 12]. MCT2 can be used to convert high voltage pulse signal into low voltage square wave signal in digital circuit.
4060 14 asynchronous binary serial counter with oscillator (14 asynchronous binary counter and oscillator)
The 4060 consists of two circuits: a 14-bit binary serial counter/frequency divider consisting of a T-flip-flop, and its frequency division coefficient is16 ~16348 (Q4 ~ Q14); The oscillator part needs an external RC or crystal oscillator, or it can be directly connected to an external clock. 4060 can provide standard time signals for digital circuits. [3][5][ 12]
45 18 double decimal (BCD code) synchronous counter (double decimal counter)
45 18 consists of two independent counter units. 45 18 can be simply connected into a multi-bit counter. 45 18 can be used as a converter from binary to BCD code in digital circuits. [3][ 12]
45 1 1 BCD- 7-segment latch decoder/driver (BCD to 7-segment latch/decoder driver)
45 1 1 can directly drive the LED. In the digital circuit, it mainly forms the terminal display of the counter with the display device. [3][4][ 12]
74 14 six anti-Schmidt trigger
74 14 is a special inverter with hysteresis, so it has strong anti-interference ability. In digital circuits, it is often used in signal shaping and oscillation circuits. [4]
3 circuit overall thinking analysis
Through the preliminary analysis of the circuit, we can see that the overall design idea of the circuit is that the display control circuit consists of 4060 and 74 14. It is used to control the counting time of 45 18, the data latching time of 45 1 1, and the time coordination between them. Pulse signal counting circuit: It consists of MCT2, 74 14 and 45 18. Used for isolation, shaping and counting of ignition pulse signals. Digital display circuit: It consists of 45 1 1, 74 14 and LED. Used to display the engine speed and control the brightness of the digital tube. Power supply circuit: composed of 7805. Which is used for providing a stable power supply for various electronic devices.
From the overall design idea, we can see the problems in the circuit shown in figure 1: the display data must reflect the change of engine speed in time, and the refresh of the display data should be about 0.5 seconds; During this period, the engine speed cannot be reflected only by counting the ignition pulses of the engine, so it is necessary to multiply the input pulses [1 1].
The number of ignition pulses per unit time of engines with different cylinders is different, that is, in order to correctly display the engine speed, there must be a certain conversion relationship among pulse counting time, cylinder number and frequency doubling number. Through further analysis, I can draw the following conclusions:
(3- 1)
Engine speed of ne, reading of ne* instrument, cylinder number of nc engine, frequency doubling of nf, and counting time of tc pulse.
Because the counting time is about 0.5 seconds and the frequency doubling number is 100, the counting time of cylinder 4 is 0.3 seconds; The counting time of cylinder 6 is 0.2 seconds; The counting time of 8 cylinders is 0. 15 seconds. Of course, you can also choose the variable frequency doubling method with fixed counting time [1 1]. The +0 circuit in Figure 65438 is not given the frequency doubling circuit, so it is incomplete and cannot display the engine speed correctly.
4 circuit analysis
4 1 display control circuit
According to the empirical formula (4- 1)[ 12] and the resistance and capacitance parameters given in figure 1, Figure 2 (the relationship between pulse counting time and adjustable resistance value) is calculated by Matlab. As can be seen from Figure 2, 4-cylinder machine needs 256 frequency division, 8-cylinder machine needs 128 frequency division, and 6-cylinder machine can do both. According to the frequency division factor of 4060, 14 pin (QH) should be selected for cylinder 4, 6 pin (QG) should be selected for cylinder 8, and both pins can be used for cylinder 6.
(4- 1)
Figure 2: Selection of 4060 frequency division coefficient
Coordinated control of 45 18 counting and 45 1 1 data latching. The fifth pin (LE) of 45 1 1 is used to latch data. When the potential of the pin is 1, when the potential is 0, the data is latched and refreshed. Pin 7 of 45 18 and 15 (RST) are used for recounting. Design idea: At the end of the last cycle, refresh the latch count data with 45 1 1, and then count again with 45 18. The period of latching and counting is determined by the 4060 pulse period. The "control pulse generation and delay circuit" consisting of three 74C 14 inverters, resistors and capacitors realizes this function. The simulation of the circuit with Protel is shown in Figure 3, and the pulse time is shortened to 3ms to clearly show the relationship between signals.
Figure 3: Control of Data Counting and Latching
4 2 pulse signal counting circuit
Isolation and shaping of ignition signal: the ignition secondary voltage of the engine is about 200~400V, which needs to be isolated by power device MCT2. In figure 1, the pin number of the signal lead-in terminal is 1, and the pin number of the grounding terminal should be 2. The isolated signal is inverted, so it is corrected and shaped by the inverter. The input and output terminals of MCT2 are connected with capacitors and diodes, which are mainly used to protect MCT2. [6]
Realization of 100 frequency doubling circuit: Reference [3] directly obtains the 100 frequency doubling circuit as shown in Figure 3. 4046 is a phase-locked loop integrated circuit, which is often used for frequency modulation and frequency synthesis.
Figure 3: Realization of100 Frequency Multiplier Circuit
Cascade in a ripple mode of 45 18: the enable of the first stage 45 18 is terminated at a high level; The Q4 output of the previous stage 45 18 is connected to the enabling end of the next stage; The clock terminal of the next stage is grounded. [ 12]
4 3 digital display circuit
Selection of current limiting resistor: LED is a nonlinear device, with a segment voltage of about 2V and a working current of about 200mA. The output voltage of 45 1 1 is the power supply voltage (5V), so it is appropriate to choose 150 as the current limiting resistor.
Control of digital display brightness: When the potential at the /BI terminal of 45 1 1 is 0, all 7 segments of the output are 0(LED goes out). This circuit uses 74 14 to form a multivibrator [9]. By changing the resistance and capacitance, pulse signals with different frequencies can be obtained, and the lighting time of LED can be controlled, so as to control the brightness of digital display.
4 4 power supply circuit
Selection of capacitor: Please refer to relevant literature [10] for the standard connection of three-terminal voltage regulator. Since the input of the power supply circuit is taken from the engine battery, the filter capacitor (electrolytic capacitor) of 1000u is not needed.
5 circuit diagram
6 concluding remarks
The structure and working principle of the circuit are briefly analyzed above. If the circuit is to be further analyzed and realized, the main work includes: estimating the circuit error, and finally determining the selection of components and circuit form; Lap test of local circuit; Wiring, plate making and production; Static debugging, dynamic debugging, calibration, etc.
refer to
1. Automotive Engineering Design Manual Beijing: People's Communications Press 200 1
2. Li Dongqiang and Song Liangyu Modern Automotive Electronic Control Technology Beijing: Science and Technology Literature Publishing House 1998
3. Wei Huaqi CMOS 4000 Series Application of 60 Common Integrated Circuits Beijing: People's Posts and Telecommunications Publishing House 1993.
4. China integrated circuit Daquan high-speed CMOS integrated circuit Beijing: National Defense Industry Press 1995.
5. Standard integrated circuit data sheet CMOS 4000 series circuits Beijing: Electronic Industry Press 1995.
6. China integrated circuit power electronics technology and motion control system Beijing: National Defense Industry Press 1995.
7. Liang Yangui's Practical Handbook of Modern Integrated Circuits: Digital Unit Circuit Conversion Circuit Volume Beijing: Science and Technology Literature Publishing House, 2002
8. Course of Circuit Schematic Diagram and Circuit Board Design, Louis Shi, Beijing: Beijing Hope Electronics Press, 2002.
9. Kang, Zou Shoubin, Basic Digital Part of Electronic Technology (Fourth Edition) Beijing: Higher Education Press 2000.
10. Kang Chen Daqin's electronic technology basic simulation part (4th edition) Beijing: Higher Education Press 1999.
1 1. measurement and control technology of special tachometer for Jin Changxing gasoline engine, 19, No.7, 2000
12. Electronic Components Manual China Electronic Network
appendix
1.Matlab calculation program (selection of 4060 frequency division coefficient)
c=0.047* 10^-6；
r=4.7* 10^3；
rj=0: 10:20* 10^3；
r2= 10* 10^3；
t=(2*(R+Rj)*C)。 *(((0.405*R2))。 /((R+Rj)+R2))+0.693)；
t 1 = t . * 64；
T2 = t . * 128；
t3 = t. * 256
t4 = 0.3
t6 = 0.2
t8 = 0. 15；
plot(Rj，t 1，':k '，Rj，t2，'- k '，Rj，t3，'-k '，Rj，t4，Rj，t6，Rj，t8)；
2.Protel analog circuit (control pulse generation and delay circuit)
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