how to build up/down stop watch using logic gate ic

[inifinitrix]

simple stopwatch using ic

it is simple when i'm using PIC to built this stop watch,

but this time i have to use logic gate ic,
is there any one that has suggestion circuit to build this watch??
or u can give me a guide or website link on how to build the circuit.
one more thing,this stop watch only use one button as an input and the
tricky part is to differentiate two types of input,i. e. the quick click vs. the long depression,by use only 1 button

somebody help me,
thanx

 

[safwatonline]

up-down counter with gates

u need something like 555 as a clock and a simple up/down counter and some decoder for 7 segment and some seven segmments

 

[VVV]

up down switch using pic ic

What is supposed to happen after a quick click and what about the long on time?

You can use an oscillator and counters to implement this stopwatch. Is it supposed to work both as an up and down counter? In that case, it hink programmable counters are advisable. How is the selection between the two modes supposed to be done? Using another switch?

 

[inifinitrix]

stopwatch using ic

thanx dude,

the operations of the stop watch - start,stop,reset - r controlled by quick clicks of the push button.by holding down the push button for more than,say,1 second the stop watch toggles between up counting and down counting.i hope that someone give me a guide to solve this problem.

it all using only one button and i need to solve this trick by not using a programable device.i'm only use PIC as a decoder/driver for my matrix led screen (it will display word 'STOP','START','RESET', the number that i count,and some extra function that i will add later ).this just as extra feature.in the same time i also using 7 segment display.

1 more,besides 555,what can i use as a clock??

 

[VVV]

stopwatch 00.00 with 7 segment circuit

OK. A modulo-3 counter will do the trick, if you feed the (cleaned-up) pulses from the switch. In the 00 state, your stopwatch will be reset. In state 01 you enable the counting. From state 10 you return to state 00, where the display is again reset.

Now, for detecting the long pulses, use a 555, which you hold in reset using the signal from the switch (or inverted, using a gate). When the switch is depressed, the 555 is released from reset. If the switch is held depressed just for a short time the 555 does not have time to time out and when you release the button it goes back to its reset state, althought there was no pulse at its output.
However, when you hold the button down long enough for the 555 to time out, its output pulse is used to reset the modulo-3 counter above and to toggle a flip-flop that changes the mode from up to down or vice-versa. So, when you hold the button down long enough you switch the mode and reset the stopwatch. When you just press the button for short periods of time, you go through the normal stopwatch functions.

As a clock source I would not recommend the 555. A quartz oscillator followed by some dividers will ensure good accuracy.

 

[neils_arm_strong]

stopwatch circuit with simple ic

A simple counter using flip flops can be used.First you need a clock source.Then divide this clock source into three modules.One for seconds,one for minutes,one for hours.Connect appropriate clock inputs to appropriate counters. the count can be displyed on a LED display.

 

[VVV]

how build a circuit for a start stop switch

In the previous post, I forgot to mention that in state 10 you stop the counting, but keep the counters not reset, so you can see the time.

Here is another example of you you can build your 1-second delay circuit. R3 should be much smaller than R4. The switch is the same as the one used to scroll through the functions.
When the switch is open, the cap is discharged. When the switch is depressed, the cap begins to charge up. But the output cannot change unless the voltage on the cap reaches the threshold of the gate. Thus, if you release the switch quickly enough, the cap does not have time to reach the threshold and the output never changes. But if the switch is held on for a longer time, then the cap will reach the threshold and the output will change. You can use that output to reset your "function" modulo-3 counter.

The two gates driving the transistor will allow you to use pretty much any resistor you want for R1, without having to worry about the transistor base current.

 

[inifinitrix]

stopwatch using logic circuits

wow!

u r a genius.anyway thanx VVV.there r a lot things that i need to learn from u.1 more,how to divide the clock source into seconds,minutes and hours??

 

[VVV]

downstops en rc

It sounds like you only need 1 second resolution. That makes things easy.
Use a watch crystal and build an oscillator with it. The frequency is 32768Hz. That is 2^15 Hz. So you see, you just need to divide that number by 2^15 to get 1 second.
So you can use cascaded binary counters, like 74x93, 4 packages, and take the output from the C output of the last one. There are also some good CMOS counters, I think in the 4000 series, which can do all the division for you in one package.
Once you have the second, you will divide it using decade counters, but you need to create some feedback on the tens counter, because it has to reset when it reaches 6, since the seconds counter must roll over at 59.
The same applies to the minute counter.
For the hours things get a little more complicated, but esentially it works out to a similar thing: use the signals on the counters to reset them when a certain "number" is reached.

 

[inifinitrix]

show the logic of start-stop circuit

how to build a circuit that give more than 1-second delay(maybe 3 second)?? is there any calculation between R and C??

 

[VVV]

quartz stop watch ic

The threshold for the 74HC14 is between 0.5 and 0.7 Vdd. Assume it is 0.6Vdd.
Then, the cap has to charge up to 0.6Vdd to turn on the gate.
The cap charges according to the equation:
Uc=Vdd*(1-exp(t/RC))
0.6Vdd=Vdd*(1-exp(-t/RC)
0.6=1-exp(-t/RC)
-0.4=-exp(-t/RC)
0.4=exp(-t/RC)
ln0.4=-t/RC
RC=-t/ln0.4

Your t is 3 s.
Therefore, RC must be 3.27s. (I did not have to go through all that calculation, knowing that one time constant is 0.63Vdd, so I could have just said that if you want 3s, you should select RC to be 3s, but I wanted to show where it comes from).

Choose for example R=100 kohm and calculate C=3.27s/100000=32.7uF
Use a good 33uF Ta capacitor, to make sure the leakage current will not prevent the circuit from functioning.