Second and Minute counter

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appleseed

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Hello

I am working on a project that uses 3x(74LS192 + 74LS47 + 7-segment display)
and works with a frequency input. With a frequency of 1Hz it counts seconds 0-59 and minutes 0-9.

For the MSB of the seconds (by that i mean the BCD MSB) i 'm thinking of putting Q0 and Q2 outputs of the respective counter in an AND gate and the AND gate's output in the CLR input of the same counter as well as in the UP input of the minutes counter.

How does it sound?
 
If you are using gates to detect a 9 on the first digit, a 5 on the second digit and using that output to enable the first minutes counter to count the next trigger pulse then yes.
 
I just realized, you would also want to reset the seconds chips on the next count after 59.
 
guys somethind weird is happening.
i just finished building an up-down counter with 3 74192's that uses button switches to control the counting sequence (up or down)
the problem is that when i put in a square signal of, say, 10Hz, both ways of counting can only work right when the source voltage is 5.1 Volts and the signal Voltage is 2.1Volts Peak to Peak. If i try to alter the signal voltage, only one of the counting procedures will work correctly. For example, for signal voltages >2.1VPP the up-counting works correctly , but the down counting works on a higher (?) frequency, or counts in anorthodox ways (01, small pause, 23, small pause etc.) Any ideas why would something like that happen?
For frequency voltage <2.1 VPP the down counting works but the up has the same behaviour discribed above.

Oh and similar stuff happen when i change the source voltage (values between 2.5 and 5.5)
 
got bypass caps? how clean is your power supply? got any unconnected inputs?

how about posting the schematic?
 
I cant post the schematic now...
Even if there are unconnected inputs or such parameters, i think it does not make sense that despite the fact that the circuit is working (has the potential to work) fine, there is one standard behaviour that both counting ways adopt, and the only thing that changes is the voltage.
About the schematic, i know it's a working one because others have used it and built the circuit in the past and the cable connections have been checked many times.
Another thing :
One 74LS47 is of different brand than the other two, but the same characteristics (though i really dont think that this is the problem, because i tried connecting the signal directly in the UP/DOWN pin, keeping the other on HIGH)
 
“the signal Voltage is 2.1Volts Peak to Peak” leads me to believe you are using an AC input above and below ground. The trigger needs to alternate between +5V and ground. If your signal is +5V and open, then you need a pull down resistor to ground it.
 
appleseed said:
I cant post the schematic now...
Even if there are unconnected inputs or such parameters, i think it does not make sense that despite the fact that the circuit is working ...
Click to expand...
sigh...

first off, how can you expect us to help if we can't see what you actually did?? we are just stabbing in the dark.

now, unconnected inputs are floating. while you might think they are going to be random, they may well follow what nearby signals are doing thus appearing not so random. clydes point is also valid, with out pull ups on inputs, they may float and thus be random. so, until you tie down or up all the inputs, you can never be sure. sorry but that's just sloppy workmanship.
 

no its not. its last minute workmanship. Anyway there are no floating inputs and you dont really need to see the schematic because theres really only one way to do it. today i tried setting the signal DC offset to 1 Volt and it works just fine. But when i set it to 2 Volts, which sounds more reasonable because that way the signal alternates between 0 and 4 Volts, the same thing happens.
 
I'm not sure I get the distinction between last-minute and sloppy.

You did imply that there were floating inputs. if there weren't any, there's no argument. I still think unconnected inputs are sloppy.
 
philba said:
I'm not sure I get the distinction between last-minute and sloppy.

You did imply that there were floating inputs. if there weren't any, there's no argument. I still think unconnected inputs are sloppy.
Click to expand...



sloppy workmanship is generally unintended, last-minute workmanship's cons are well knonwn and accepted
 
Check the datasheets... make sure you're using TTL ICs (if they're CMOS then DEFINITELY check the datasheets because there's so much damn variation). If you haven't already, hook your input up to a CRO and check for noise.

Other than that (and more likely) I agree with everyone else -- it's probably the floating inputs.
 
What!?

If you're working with 2Vpp then you're alternating between 1V and 3V.

If you're using a 1V offset, you're alternating between 0V and 2V. Check the data sheets for values of VIL and VIH to see why this is better for TTL.
 
Why no schematic? This is something I could really use right now. I started roasting coffee at home a few weeks ago. It takes about 7 minutes and a few seconds. I don't have any clocks with seconds, also have 4 x 7 segment LEDs almost 2 inches tall...
 
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