Back to basics for me :D

[john_edmunds]

Hi Folks, 
 First post here. An avid watcher of EEVblog (especially the fundementals) I decided recently to start re-learning electronics (sort of) for the first time in since 2000. I have begun making the obligatory Nixie clock using 4000 series logic, but have run into a wall and would appreciate any help.

I am using a 4060/4013 combo to feed a 1 hz clock pulse into a 4017 counter. I then cascade these together to give me seconds/ tens of seconds, then minutes/ tens of minutes. Both sets of tens, the number 6 output is tied to the reset line to make sure that it counts from 0-59 in both tens and minutes. This works a treat for both the minutes and seconds, but does not quite work with hours due to the need to count to 12/24.

This is where I have become stuck.
 I had originally used 2 more 4017s, but it can only count to 20. I was toying with a another counter that would trigger a reset when it counts the 2 output a second time, but this would trigger another carry out. This is all becoming a spiralling mess of counters

 Is there any easy way to either count to 12 or 24 and have it ouput the number onto the nixies or am I barking up the wrong tree.

 (The nixies are IN-12s with ULN2003A with the +ve rail provided by a 160v boost converter)
 I can post a screen of my schematic as it stands if this would help.

 Cheers for any suggestions

 John

[PA0PBZ]

I had originally used 2 more 4017s, but it can only count to 20

2 Cascaded 4017's can count to 99, I think your problem is that you have to craft your reset from either 13 or 25 which needs some more logic gates.

[john_edmunds]

Thanks for the response.

 There was a short circuit between my chair and the keyboard . The way I have it set up a the moment it only counts to 20. My apologies, I should have been more specific. Whilst I like the idea of shaving 4 hours off of each day as it means my Birthday will come around quicker and I get to eat more cake, probably not a great idea over all.

I was wondering about using a couple of shift registers and shift each time an hour passed, when it hits 12 or 24 hours, use this to trigger a reset, but it seems a bit cack handed and I've not really played with those before so not sure how possible it it.

[ArthurDent]

As posted above you need some logic gates. For hours you have 2 decades, units and tens. connect a two input AND gate to decode 13 from tens/units and another AND gate to decode 24. have the outputs from these two AND gates go to a SPDT switch to select which mode (12/24) you want and that selected signal can be the reset for hours.

[john_edmunds]

Aha.. I see now. I hadn't thought of using logic gates . I still have a lot too learn.

Thank you both kindly for your help. 

I'll go back to the bread board and hook it up, I'll let you know how it all goes

Cheers.