| Electronics > Projects, Designs, and Technical Stuff |
| digital clock with an alarm |
| << < (2/2) |
| Chriss:
I'm not sure but it smells to me like a spiky bouncing switch. If you have a scope try to measure the power line and see if there is some noise in the power rail. It is like you turn on/off rapidly the power for the device... Sent from my SM-J500F using Tapatalk |
| phlegeton:
On the schematic it's hard to see.. but are you using decoupling caps on the IC's ? |
| tooki:
Lemme guess, in reality you’re in the same class as this guy who just posted, too? https://www.eevblog.com/forum/projects/12-hr-digital-clock-with-an-alarm/ |
| Rajan Shah:
No, I don't know him. By the way, could you give me any ideas? |
| phlegeton:
There are already a few suggestions mentioned in this topic. Did you already took a look at them ? A couple of things I can think of: - Did you measure voltages ? - If the counting always starts at 20, and resets at 40 , it looks like you swapped some bits. - Are the 7490 configured for Bi-Quinary ar BCD count ? - As mentioned earlier in this post: check for spike on the voltage rail, make sure you use decoupling caps. - If you have a scope (and when playing with digital circuits, you should have one) probe around. Measure stuff. To troubleshoot, go back to the basics. Which means, check each and every portion of the circuit. So disconnect reset and alarm portion of the circuit. Next test each counter and display driver individually, check if each counter counts from 00-99. (and as a bonus, since you use the 7447 ,use the test lamp feature to test each segment of your displays) Next, connect the reset part of the circuit. Test if each counter reset at the right count. And that each counter in the chain receives a correct pulse. Then connect up the alarm part of the circuit and test it. But this is basic troubleshooting stuff.. |
| Navigation |
| Message Index |
| Previous page |