Stop Watch Without Programming

Hey guys,

For all beginners, here is a cool project that you can create without programming. It is simple and also cost effecient.

Before getting started, let's have a look at the parts list:

ICs used:

1) 555 timer- x1

2) CD 4081BE(AND gate)- x1 " "

3) CD 4071(OR gate)-x1 " "

4) CD 4026B -x3 " "

Other components:

1) 7- segment digital display- x3 " "

2) Push button switch(RESET) -x1

3) Push button latching switch(PAUSE) -x1 " "

4) ON/OFF switch -x1

5) Relay switch(DPDT/SPDT)- x1

6) 1kilo ohms resistor-x2

7) 10 kilo ohm variable resistor- x1

8) 100 microfarad capacitot- x1

9) 470 ohm resistor-x3

10) 0.1 micro farad capacitor- x2

11) buzzer- x1


13) 10 kilo ohm pull down resistors-x7

14) Battery 9v and a battery cap

15) 7805 voltage regulator-x1

Step 1: Working of the Circuit

I created this circuit as a stop watch for my work out. I designed the circuit in such a way that it gives me a buzzer indication for every 10 seconds.

The IC 4026 here drives the 7 segment display. It increments the count by 1 every time it receives a pulse (low to high transition of the pulse). The pulse is generated using the timer IC 555 which is connected in astable mode. The output of the 555 ic is then connected to the clock input of the IC 4026 (pin 1). This 4026 IC ( ic in the top right corner in the schematics) is directly connected with the 555 ic.

When the number in the IC4026 has reached the number '9', it then starts from zero and sends out a pulse from its cascade pin(pin no. 5). This pin is connected to the next IC 4026 which will make it increment its count from '0' to '1'. This represents the tens place in the 'seconds' part. As the increment continues in the second's part, it must not exceed 60 (as 1 minute = 60 seconds). So, the logic gates play their important role here. Two AND gates and an OR gate with their pull down resistors are connected according to the schematics in such a way that their output is high when a certain pattern of segments unique to the number '6' gets illuminated. This output is connected to the reset pin 15 of that ic and to the clock pin of the third IC 4026.

Thus we have successfully converted that 60 seconds to 1 minute. This process gets carried on every time the seconds count reach '60'.

The 'Reset' button is connected to to pin 15 of the third IC4026 and to a relay which connects the pin 15(reset pin) of the second IC4026 so as to reset the ICs to 0.If your battery cannot deliver as much current needed to switch the relay ON, you can use an PNP transistor by connecting the base to the reset pin(via a 200ohm resistor) and its collector to the relay's coil terminal.

The 'Pause' switch is connected to the clock inhibit pin of the first IC 4026 so that it can interrupt the clock pulse and thus stop the ic from advancing its output. A '0.1 micro farad' capacitor is added to all the switches inorder to avoid debouncing problems.

The buzzer which beeps for every 10 seconds is connected to the first IC 4026 in such a way that it beeps every time it reads the number '0'. This has been achieved using logic gates.

The LEDs are connected the output of the 555 ic to indicate the clock pulse.

Thus after 10 minutes the circuit automatically resets to '0'.

Step 2: Initial Set Up

As always before starting to solder the components in a perfboard, try out the circuit in a bread board.

Do it step by step in the bread board so that you can avoid loose contact and wrong connections. After making all the connections in the bread board, it might look like a lot of wires..but you don't need to worry about that as its just for testing and you are going to convert that into a soldered one.

Step 3: Soldering

After testing out the circuit, solder them in your perfboard. Have the schematics by your side while soldering.

Make sure to use base for ic so that you can avoid damaging them while soldering.

Step 4: Powering the Circuit

In order to create this project at a low cost, i used the battery terminals from an old 9V battery to make the battery cap and hot glued them.

I have designed the circuit for 5v. So remember to use a voltage regulator(7805) to power your circuit.

Heat sink is not needed as it will draw very less current. You can also directly power it using the 9v battery but the resistor values might change.

Step 5: Outcome of the Project

This is how the circuit will work after completing it. You can make it even more compact. My stop watch is slightly big as I din't find a proper enclosure for that.

"Nothing is as pleasant as learning through exploring"



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    6 Discussions


    15 days ago

    Slight pick-up on your terminology:
    "debouncing problems"="switch bounce" or just "bounce" if it's clear from the context that a switch is being referred to.
    Nice project, it's really good to see someone making something with logic chips instead of reaching for a microcntroller for every little thing. Well done!

    1 reply