60 MOD Stopwatch- having problems in recycling

Thread Starter

Multisim

Joined Jun 13, 2018
3
Hello Users of the internet,
I'm tasked to connect up a minute or simply 60 seconds stopwatch. My only problem right now is that when i press start, the counter counts till 60 and goes back 00 but what i want for it to do, is that to re-count even without the need of re-activating the start switch. Can anyone please guide me through this mess? thank you :)

p.s. have been stucked here since 3 hours ago...i wonder is it because of my fever that might have caused me to not spot the mistake...
or most likely im just retarded lel...okay done blabbering and going to start researching and thinking :)
Wish to hear from you (anyone) soon <3

Best Regards,
Jaylee <3
 

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LesJones

Joined Jan 8, 2017
3,196
Think about what happents to Qa in U7 at the end of the count of 60. If it is working as far as you say I do not think the simulator is very good as inputs real 74 series ICs float high so the start and reset buttons would not work. Note we do not give the solution to homework questions we ask questions or give tips that should help you solve the problem yourself.

Les.
 

Thread Starter

Multisim

Joined Jun 13, 2018
3
Think about what happents to Qa in U7 at the end of the count of 60. If it is working as far as you say I do not think the simulator is very good as inputs real 74 series ICs float high so the start and reset buttons would not work. Note we do not give the solution to homework questions we ask questions or give tips that should help you solve the problem yourself.

Les.
Qa/U7 should be recycling back to 0000 then 0001 so on and so forth...hmm still processing...but the buttons work tho \_~-~_\

note: pardon my terrible english...scored 9/95 for english exam :3 hehe im such a pro in failing english :3
p.s. and im aware that people here wont give me answers but tips <3 ty for reminding me <3 appreciate it <333
 

LesJones

Joined Jan 8, 2017
3,196
There is no problem with your english. I can undestsnd it. You are using the output of Qa in U7 to control if the counter is running or stopped. (By gating the clock pulses.) Think a bit more about what happens when Qa/U7 is in the 0 (Reset. ) state. It may help to look at the block diagram of the 74LS93 on the data sheet. Don't worry about my comments about floating inputs. That is a fault with the simulator that would confuse you if you built the circuit after finding it worked on the simulator but not when built with real parts.

Les.
 

dl324

Joined Mar 30, 2015
12,873
Cropped/edited schematic:
upload_2018-12-15_10-11-25.png
I'm tasked to connect up a minute or simply 60 seconds stopwatch.
Your circuit is more complex than it needs to be. You can implement a Mod 60 counter with the counters and 2 gates. Start, stop, and reset would require a few more gates.

Please post the complete text of the problem.
My only problem right now is that when i press start, the counter counts till 60 and goes back 00
Your counter doesn't count to 60; it counts from 0 to 59.
but what i want for it to do, is that to re-count even without the need of re-activating the start switch. Can anyone please guide me through this mess?
What is your reasoning for using the QA output of the second counter to gate the clock to the LSD counter?

Learn how to use the shift key to force Multisim to make straighter routes.
 
Last edited:

absf

Joined Dec 29, 2010
1,949
Here is a simplified block diagram of your schematics...
MOD 60 BLOCK DIAG.PNG
U7 is made up of 2 parts, "divide by 2" and "divide by 8" . The "divide by 2" part is used as a flip flop for the start/stop button to allow or inhibit the clock pulses passing through U2B.

U5A and U3A would make U7 to count to "6" instead of "8". Similarly U6A and U4A make U8 to count to 10 instead of 16.

So if you want the counter to continue count up after reaching "00", you have to do something on the "/2" part of U7.
i) initiate a pulse to the "in" of U7 after the counters reaching "00"
ii) Make the clock pulse able to pass through U2B after reaching "00".

Note: If you use 74LS92 for U7 and 74LS90 for U8, you can get rid of quite a few unnecessary gates in your circuit.

Allen
 

LesJones

Joined Jan 8, 2017
3,196
Hi absf,
There is a fault in your diagram relating to the internal connections of U7. It is the same wrong assumption that the TS has made. I won't say exactly what it is or it would be the answer to the problem.

Les.
 

absf

Joined Dec 29, 2010
1,949
I had never used that part, so I wired it up in a simulator. Unless I made a wiring mistake, it has an odd count sequence: 0,1,2,4,5,6.
You are absolutely right.

After I used 74ls92 for U7 .The counter will count to "69" instead of "59". It would still need the extra AND gate to check for "110" to clear the tenth counter to zero.

Sorry that I overlooked on the behaviour of this chip.

Allen
 
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