CMOS Logic IC Clock Design and Mods - Page 1
Forum section: electronics / projects

author: n3vti
author_rank: Contributor
timestamp: September 03, 2025, 08:57:08 pm
content: Greetings all:Recently, I was watching YouTube and got a recommendation for a video: A CMOS Logic Clock by Big Clive. The kit can be found on AliExpress, so I picked up one. While I love it as is, this kinda triggered my mind in to redesigning the clock and modding it for 12 hour operation. (It also reminded me of Dave's Clock from an earlier EEVblog (801)) I had to remember the pinout of the CD4029, 4511, 4518, and so on. Not only was able to come up with a schematic for a 12 hour mod (with AM & PM as well!) but also for a Day (albeit very crude), Month, and Year counter. Although I'm not sure if I got them completely right, as it has been a very long time since I've dealt with logic circuits. Attached are the schematics for the addons I made. I forgot to add a switch to them to manually advance the count if needed (especially the Day counter, since it counts to 31 and then force back to 1, and I will need to advance it manually for months less than 31 days) This is more of a sanity check for me... do I have these right? Not sure how I will build this since I don't have any CADs or circuit design software. (Edit: Only added 12 hour mod and Day counter, due to file size limit)

author: GU754
author_rank: Newbie
timestamp: September 04, 2025, 12:57:32 am
content: Nice project! Your approach for the 12-hour mod and day counter looks reasonable. Using CD4029 for up/down counting and CD4511 for driving the display is a classic way to do it. Just make sure your reset logic is solid — for the 12-hour counter you’ll need to reset at 13 (or at 1, depending on how you wire it) and flip the AM/PM bit at the same time.For the day counter, you might consider adding a simple DIP switch or push button for manual advance, as you mentioned — that will make it much easier to handle months with fewer than 31 days. If you don’t have CAD software, even a simple stripboard build should work fine for testing before you commit to a PCB.If you want to expand later, you could cascade another counter for months and add a basic AND gate network to reset at 30 for April, June, September, November, and 28/29 for February. But for now, what you’ve drawn should work as a sanity check.

author: n3vti
author_rank: Contributor
timestamp: September 04, 2025, 03:08:32 am
content: For the reset logic, i have 3 AND gates shown. When the 4029 recycles to zero, the Carryout briefly goes Low, and then back to High, which triggers the one Flip Flop. The 4027 handles both the AM/PM and the +10 hours. With the +10 hours high, when the 4029 hits 2, it triggers the AND gate High, which triggers the other Flip Flop, which is the AM/PM. With both And gates active, on the next count, it triggers the final AND gate, which sets the +10 hours Low, and Preset Enable High, which loads 1 in to the 4029. Cycle repeats. I had to add in an extra diode, because without it, it would constantly trigger the Preset Enable, and it wouldn't count. (doh!) Pin 14 of the 4027, which is (technically) the AM indicator, when it goes high it triggers the day count +1. I'm thinking of adding a switch at the start of the Day counter, and a switch at the final AND gate (which triggers the Month +1 and resets Day to 1) Year is pretty straight forward. I try to use a positive clock when I can.Hope this wasn't too confusing...(month and Year schematics attached)