# Digital Logic Clock

Discussion in 'Homework Help' started by sulleylovesmike, Mar 23, 2015.

1. ### sulleylovesmike Thread Starter New Member

Mar 23, 2015
1
0
Hi

I've created the following circuit on a breadboard in class, and we need to modify it to display hours and minutes as well as seconds. I know I will need 6 x 7 segment displays, and that I want the first couple to reset after 23, the second and third couples to reset after 59. As it is, it resets after 99. How do I get it to do what I want? It's using a 74LS163 up counter, a 7447 BCD decoder and a 555 timer along with 7400 NAND gate, 7432 OR gate at 7404 Inverter.

Thanks

2. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
The first thing is to understand how the circuit you currently have does what it does.

Can you describe what the roles of the four pieces of glue logic are (the two NAND gates, the OR gate, and the NOT gate)?

I haven't looked at it in detail, but given the values that the two NAND gates are picking off, I don't think it behaves like you are saying it does.

Also, you should never leave unconnected inputs floating. The simulator might not care, but presumably you want to eventually make circuits that work in the real world. Always tie unused inputs to an appropriate logic level.

3. ### MrCarlos Active Member

Jan 2, 2010
400
134
Hello sulleylovesmike
Also, the I/O BI/RBO PIN in the 74LS47 could be unconnected because it is tied internally.
Something else: If you connect a single current limiting resistor for the Display's, the most segments turn on, the lower in bright segments.
You Should Use one current limiting resistor for each segment on each Display

As you should know: The 74LS163 is a synchronous 4-BIT binary counter IC. They count from 0 to F.
So, the first thing you shall do is to setup your counters to count from 0 to 9.
Then setup your counters to count from 00 to 59. At the next clock pulse should change to 00.
Take in consideration that your IC counters are synchronous, so when the units counters, either seconds o minutes, reaches 9, you must reset it to 0.
And when a couple reaches 59 should change to 00. Yes, At the next clock pulse.

You followed me throughout this Palaver?
The same mechanics could be applied to the couple of counters used for the hours.

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