555 timer and counter comprehensive application circuit

Topic
 
555 timer and counter comprehensive application circuit
 
Topic analysis
 
This nine-way water lamp controller can control 9 lamps to cycle and emit light, and the water flow speed can be adjusted. After power on, NE555 and peripheral circuits form a multivibrator. The oscillation frequency is mainly determined by R1, R2, W and C3. Adjusting W can change the oscillation frequency. The oscillation signal of the oscillator is output from pin 3 of NE555 and sent to the counting input terminal (pin 14) of CD4017. Every time a pulse comes, the high level of the counter's 00-9 output moves 1 bit in turn, lighting up the corresponding light-emitting diode, thus creating a feeling of running water. Q9 is connected to the reset terminal and plays an automatic reset role, that is, after the count is full, it starts counting from the beginning, so that the circuit continues to cycle.
 
555 timer internal block diagram
 
The basic block diagram and pinout of the 555 timer are shown below. The 555 timer usually adopts an 8-pin DIP package. The 555 consists of 2 comparators, a voltage divider circuit, a trigger, a discharge transistor and an output circuit.
 
 
 
4017 counter
CO: carry pulse output
CP: clock input
CR: clear
INH: disable
Q0~Q9: count pulse output
VDD: positive power supply
VSS: ground Note: CD4017 is a CMOS chip, and the input pins cannot be left floating.
 
Schematic Design Instructions
 
Experimental Document
 
Fill in the blanks according to the circuit schematic and related knowledge of integrated circuits
 
1. The 555 timer has a resistor divider composed of three 5 kilo-ohm resistors. If the power supply voltage is VCC, the potentials of the two voltage divider points are respectively and .
2. For the 555 timer, if the input of pin 4 is low, the output is . 3.
There are two voltage comparators in the 555 timer. If the voltage at the in-phase input of the voltage comparator is less than the voltage at the reverse input, the voltage comparator outputs .
4. Turn on the power supply, use an oscilloscope to observe the waveform of pin 3 of the 555 timer output, and draw the corresponding waveform in the table below.
 


Waveform of pin 3 of the 555 timer


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 


 
5. What is the relationship between the output signal of pin 12 CO of CD4017 and other Q0~Q9?
                                                                                                   
6. If the 15th pin CR of CD4017 is high, the input Q0~Q9 .
7. According to the actual measurement and results, the function of CD4017 is verified.
 


CD4017 function table


CP


INH


CR


output Q0~Q9


×


×


H


 


↑


L


L


 


H


↓


L


 


L


×


L


 


×


H


L


 


↓


×


L


 


×


↑


L


 


 
8. According to the function table, the condition for CD4017 to count normally is summarized as follows.
 
Physical display description
 
 
demonstration video