1, familiar with the basic working principle of digital frequency meter.
2. Familiar with the comprehensive design and debugging method of counting display and control in digital frequency meter.
Second, the experimental principle
Digital frequency meter is one of the instruments for measuring the frequency of electrical signals, and its schematic diagram is as follows:
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The measurement signal is amplified and shaped into a pulse signal, which is used as the counting pulse of the counter. The counter is controlled by a control gate. When the door is opened, the counter begins to count the input pulse signal. If the door is open 1 sec, the number of pulses accumulated by the counter is the frequency of the measurement signal. After the door is closed, the counting stops, the state of the counter is written into the latch, and the decoder drives the digital tube to display the measured value. In this way, when measuring (counting) again, the digital tube can keep the data measured last time.
Third, the experimental requirements
1, using 555 timer to design the standard second pulse generator circuit.
2. The decoding display circuit adopts four digital tube display circuits in the experimental box.
Fourth, design ideas.
According to the experimental principle block diagram, the following design is made: the signal amplification part can be completed by triode amplification circuit, the shaping part can be completed by Schmidt trigger, and for simplicity, it can be completed by 555. The control gate can be realized by an AND gate. The two monostable flip-flops are exactly the same, and both can be made of 555. The counter is completed with 74LS 160, which saves the trouble of connecting decimal counters (if 74LS 16 1). The latch circuit is completed by four latches 74LS75. Its output can be directly connected to the 74LS247 decoding circuit on the digital box, and then the result can be displayed.
Four frequency meters are designed in this experiment, so four 74LS 160 and four 74LS75 are needed.
Verb (abbreviation of verb) experimental equipment
555 Timer 74LS160 74LS75 74LS04 74LS00 Some resistors and capacitors.
Sixth, design ideas.
This paper mainly explains the selection of some parameters.
For Schmitt trigger, only a small external capacitor is involved, with a typical value of 0.0 1uF.