This LED based stop watch circuit can be worked as a clock in this counter will advance after every one second. When you provide power supply it start it’s counting from zero and you can stop the timer any time with the help of switch.
In this circuit you can monitor the time from 1 second to 60 minutes. It can be used while cooking or while doing exercise or in laboratories. It can be used by students preparing for competitive exams. Important feature of this circuit is you can switch off the stop watch any time with the help of switch S1 and it will hold that value.
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This circuit commonly used IC NE555 timer, wired in astable mode and CD4017 counter/divider IC.
In this circuit NE555 astable generates a clock for the circuit, which provides a oscillating wave to the output pin 3 of IC1. You can vary the speed of oscillation with the help of R2. The frequency of oscillation of 555 timer can be calculated by:
f=1.44/(R1+2*(R2)*C1)
And time period can be calculated by-
T = 0.7*(R1+ (2*R2))*C1 in seconds
Here
R1 = 10K
R2 = 68k
C1 = 10uF
Therefore T=1.01 Seconds
CD4017 is a CMOS counter/ divider IC. It takes clock signal from the clock input and turns on the 10 output in sequence, each time when it receives clock input pulses.
In order to understand the working of IC one must know about its individual pin. It has 3 input pin and 10 output pin and one is ground pin and another is used for power supply and one is Carry out pin. Pin diagram of CD4017 is shown below-
1. Input pin-
a. Reset pin (pin 15) – It is used to reset the counter to zero. Like you want the counter to count up to third output then connect the fourth output to pin 15. Now after every third output it will automatically starts counting from zero.
b. Clock pin (pin14) – Whenever pin 14 goes high it will provide you the output. Like for first clock pulse pin 3 will provide you output similarly for next pulse pin 2 will provide output and so on. After 10 pulse it will again start from Q0 output.
c. Clock Inhibit pin (pin 13)- It is used to switch the counter “on” and “off”. When you want to switch off the counter then pin 13 should be high. If it is high it will ignore the clock pulse no matter how many times you press the switch means the count will not advance. In our circuit we have ground the pin 13.
2. Output pin (pin Q0- Q9)- It is used to receive the output in sequential manner. Like for first pulse pin 3 will provide you the output and so on.
3. Ground pin (pin 8) and Supply pin (pin 16)- It is used to provide ground and power supply to the IC for its working.
4. Carry out pin (pin 12)- It is used to connect one or more CD4017 IC’s. Like if you want to add one more CD4017 IC then connect Pin 12 to Clock input of its successor. The carry pin of first CD4017 is connected to clock input of second and the carry pin of second is connected to the clock input of third and so on.
Woking of this circuit is very simple when you on the switch S1, NE555 timer start oscillating and output from pin 3 of IC1 is provided to CD4017 decade counter pin 14, which provide a clock pulse for the working of IC2. Here after receiving the clock input CD4017 starts its counter from zero (as it has inbuilt counter). And it advances one by one each time pin 14 goes high. Like first we get output from pin 3 that is Q0 and LED1 will glow and then from pin 2, LED2 will glow and so on.
And when counter reaches to 10 pulse LED11 start counting as you can see from circuit diagram we have cascade the IC by connecting the 12 pin of IC2 to Pin 14 of IC3. So after 10 pulse it make the pin 14 of IC3 high. Now IC3 will start its counting in seconds from 10 seconds to 60 seconds because we have connected the pin 5 to reset pin 15 so it will count only up to 60 seconds. Then IC4 starts its counting again, we have cascade the IC3 to IC4.
In short IC2 counts from 1 to 10 seconds, IC3 counts from 10 seconds to 60 seconds; IC4 counts from 1 minute to 10 minute and IC5 counts from 10 minutes to 60 minutes. So now at any point you can calculate the time by seeing the number of LED’s which glow. For example IC1 LED number 3 is glowing and IC2 LED number 2 is glowing than time will be 23 seconds.
Circuit Diagrams
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Filed Under: 555 Timers, Electronic Projects
Filed Under: 555 Timers, Electronic Projects
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