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  #1  
Old 11-08-2010, 03:05 PM
aboutsc aboutsc is offline
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Default MOD-60 counter with stop/start and reset buttons

HI all

I am given an assignment by my lecture. We are using two 74LS93N(4 bit binary counter) ICs to build a 60 seconds stopwatch. I have no problem building MOD-60 counter from 00 - 59 and it will reset to 00 when it hits 60. I have connect the these two 74LS93N to two 7 segment LED common Anode. I use MOD-6 and MOD-10 to come up with the MOD-60 counter.

However, I do not know how to add in stop/start and reset buttons. The reset button switch will clear or reset the mod-60 counter to 00 when activated. ie, 00 until it is started again through the use of the start/stop switch.

If the mod-60 value is running , activating the start/stop switch will stop the counter at its current count value, ie, 40, which indicates a time lapse of 40 seconds from the start. Reactivating this same switch will cause the mod-60 counter to resume from this previously stopped value.

We are given one 74LS00 and one 74LS32 as well.

PLEASE DO HELP ME!!!

THANKS

CURTIS

P.s I have read through another post which had been posted here for quite sometime. But it is different from my case.
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Old 11-08-2010, 05:11 PM
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It would be interesting to see your schematic. Achieving a mod6 and mod 10 count from binary counters using only one 'LS32 sounds challenging.

If you have the data sheet for an 'LS93, you will notice some reset pins. You could also reset on a count of 3Bh
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Old 11-08-2010, 07:14 PM
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As for the stopwatch function, you could filter the clock pulses from reaching the IC with a AND or NAND gate.
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Old 11-08-2010, 09:58 PM
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What are you using for a clock? I assume you are using the MR1 and MR2 inputs to implement your Mod n functionality. The 74ls32 can be used to also allow an external signal (reset switch) or the data signals to reset your chips. You can isolate the first flip flop of the 'ls93 used for the Mod 6 counter and use it as a latch for start/stop, since you only need the last three outputs for Mod 6. This latch can be used to gate the clock into the Mod 10 counter. You have the 'ls00 for gating the clock pulses.

Last edited by djsfantasi; 11-09-2010 at 04:48 PM.
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Old 11-10-2010, 02:17 PM
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Have you had any success? Please let us know.
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Old 11-13-2010, 05:41 PM
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how do you use the 74ls32 to allow a switch to reset the the ics?
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Old 11-14-2010, 07:04 AM
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Basically my friend came out with this. It does work. But I want it to recount again from 00-59.

When I give a Logic low signal to the start/stop button, the counter will start counting and reset the whole counter when it hits 59. After that it will stop at 00 and wait for the next push to Logic low.

Thanks you all for your reply!!!

CHEERS
CURTIS
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Old 11-14-2010, 01:13 PM
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Zowie - where did you scare up the 74F00? You will need triple decoupling caps to get your counter to run with that glitching monster in there. Hope you remembered to tie those unused inputs to ground.
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Old 11-14-2010, 03:52 PM
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Quote:
Originally Posted by beenthere View Post
Zowie - where did you scare up the 74F00? You will need triple decoupling caps to get your counter to run with that glitching monster in there. Hope you remembered to tie those unused inputs to ground.
Hope you can explain more on this. I do not really understand this.
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Old 11-14-2010, 06:11 PM
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&4F logic is very old. It was done in an attempt to make logic that could clock faster than the standard 74xx and 74LSxx logic. The output stage exhibits a goodly amount of shoot through, so the Vcc bus handles lots of current and switching noise (big current spike with every gate output transition).

For all logic whatever, unused inputs that are allowed to float will do so right at the operating level, causing the output to oscillate. The oscillations may cause the IC to fail. Since you are dealing with TTL, you can tie inputs to ground, or else pull them up to Vcc with a resistor (not needed to CMOS). Use 20K for 74LSxx, and 4.7K for 74Fxx.
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