Author Topic: 12 hr digital clock with an alarm  (Read 975 times)

0 Members and 1 Guest are viewing this topic.

Offline Sangharsh SharmaTopic starter

  • Contributor
  • Posts: 15
  • Country: np
12 hr digital clock with an alarm
« on: July 17, 2019, 01:41:29 pm »
Hello everyone. I've been trying to design a 12 hr format digital clock with AM/PM and an alarm setting. The problem that I always encounter is that the count always starts from random values. And, it continues to do so. What should I do so that when I connect the power supply it starts from 00:00:00? Also, I've used two push buttons to increase count of minute and hour. Sometimes, the circuit works and it doesn't. The count gets all random in the hour clock all of a sudden. I've got to demonstrate this project in 2 days. What do I do? I haven't been able to diagnose the error.
I've used 7490, 7447 ICs. For the alarm, I've used DIP switches and 7485 ICs. I've attached an image below. This is how it starts when I give the power supply.
 

Offline NivagSwerdna

  • Super Contributor
  • ***
  • Posts: 2507
  • Country: gb
Re: 12 hr digital clock with an alarm
« Reply #1 on: July 17, 2019, 01:56:04 pm »
Hold reset on the counters for a while at start-up.  Traditionally a 555 timer would be used for this purpose
 

Offline JagV12

  • Contributor
  • Posts: 25
  • Country: fr
Re: 12 hr digital clock with an alarm
« Reply #2 on: July 18, 2019, 04:45:39 pm »
That large screen capture of your screen displaying a picture of the breadboard assembly is pure waste. We believe you.

Pin 2 & 3 of every 7490 counter should be pulled high for a few ms at startup (NE555 or equivalent or capacitor (or reset button) connected to V+ rail with resistor to GND) while pin 6 or 7 (or both) is (are) held low all the time.

By the way, real AM/PM clock start at 12:00 and end at 11:59 as per the big mess endianness |O... (and I'm sure you can do that !)
 
The following users thanked this post: tooki


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf