Adding alarm to Digital Clock

Thread Starter

Q-ball

Joined Apr 16, 2019
2
Hi folks,

I'm new to the site as a user. I'm currently in the middle of a project for school where I'm building a 12 Hr digital alarm clock. I've got everything except the alarm figured out. This is all done using 7490 and 7492 ICs along with the 7447s and Seven Segment displays.

Where I'm hung up at is the alarm. My partner and I are trying to switch the display from showing the time to displaying the alarm time in order to set it. I was wondering if something along the lines of tri state buffers could be used for something like that. I'm not looking for the answers themselves, but maybe a direction to look in. Also looking for information on how to set an alarm. I'm guessing some sort of comparator setup? Or an IC that can do that is built for that purpose?

Any help is greatly appreciated!
 

djsfantasi

Joined Apr 11, 2010
7,826
So this is schoolwork! It belongs in the Homework Help forum.

I’ll give you one hint. But we’re supposed to guide you to a solution; not provide one. Investigate 2:1 demultiplexors. One select signal chooses between two sources.

How are you going to set the alarm time? And how are you going to tell when the alarm time has occurred?
 

AnalogKid

Joined Aug 1, 2013
9,352
Hint - this is conceptually easy, but it will take over a dozen additional chips to implement.

Also - multiplexer, not demux. Many CMOS parts are bidirectional. TTL parts are not.

ak
 

Thread Starter

Q-ball

Joined Apr 16, 2019
2
Thanks folks! I’ll definitely check out the multiplexers. I did say I was not looking for the answers, rather the direction. Thanks again.
 

djsfantasi

Joined Apr 11, 2010
7,826
So this is schoolwork! It belongs in the Homework Help forum.

I’ll give you one hint. But we’re supposed to guide you to a solution; not provide one. Investigate 2:1 demultiplexors. One select signal chooses between two sources.

How are you going to set the alarm time? And how are you going to tell when the alarm time has occurred?
Oops! Mux or demux. One of those. I always get them confused. :(
 
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