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Stopwatch circuit with milliseconds

abuhafss

Aug 3, 2010
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Hi

I am looking for an accurate Stopwatch circuit with a time resolution of 100ms.

The display is required on 4-digit or 2x2-digit 7-segment LED.
Maximum time 99 seconds.

The circuit may be with or without µC or Arduino.

I prefer separate buttons for Start and Stop but a single button is also acceptable.

I Googled but could not find some suitable option.
 

Chemelec

Jul 12, 2016
291
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Jul 12, 2016
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Lots of these are Available on Ebay, From China with free shipping.
Many Under $10

Not as Kits, but you can't beat the Price.
 

kellys_eye

Jun 25, 2010
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Any timer displaying 'seconds' could be readily adapted to mS simply by changing the programmed divisor that produces the 'count' pulse.

In the case of a discrete construction this would mean (for example) leaving out the last divider in the timing chain and getting 1/10th second (or leave two dividers out to get 1/100th second etc) pulses.
 

KMoffett

Jan 21, 2009
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"The display is required on 4-digit or 2x2-digit 7-segment LED.
Maximum time 99 seconds."

Sounds like a class assignment.

Ken
 

abuhafss

Aug 3, 2010
348
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"The display is required on 4-digit or 2x2-digit 7-segment LED.
Maximum time 99 seconds."

Sounds like a class assignment.

Ken

Of course, not.
I need it to integrate it in my project. First I was thinking of utilizing some cheap stopwatch and it was fairly easy to adapt. But I gave up only because of the tiny digits. I decided to built my own circuit but I don't have experience of working with 7-segment LEDs. So I am seeking help here.

I found a lot schematics but almost all of them have 1sec time resolution or displays without the decimal point. Also I have very little experience of programming µC or Arduino.

And by the way, maximum time is 60 seconds (not 99 seconds, my mistake)
 
Last edited:

kellys_eye

Jun 25, 2010
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The decimal point can be simply hard-wired 'on' as required.

Find a circuit that uses (say) a 1MHz crystal and the 4017 decade divider (or the 7490 - old-school stuff) but instead of dividing the signal down to 1 second intervals simply tap the clock off at the 1mS interval (1kHz point).

1MHz (xtal) divide-by-10 = 100kHz
100kHz divide-by-10 = 10kHz
10kHz divide-by-10 = 1kHz (the mS timing range)
and so on
..
1Hz - the 'normal' signal used to count seconds.

Many such circuits are designed as frequency counters - the 7490 was a classic for this, used in conjunction with the 7447 BCD-seven-segment driver. Should be loads of schematics on the interweb.
 
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