Electronic Circuits and Projects Forum

Hey guys,

I have a final project which is a 12 hour clock counter. Now I've seen the forum threads about them and they go about the whole thing their own way. Now me being a student I'd actually like to learn rather than people giving me the answer. I have the minutes and seconds part of the clock done. That was easy but the hard part is the 12 hour. You can't use a 7490 because it doesn't have a preset. Which is what I wanted to use for the clock to go from 12 o'clock back to 1 o'clock. I want to clear the 1's clock at 10 which also clocks the 10's to 1. Which is 10 o'clock then have a NAND gate that will enable preset at 1 from 10's and 2 from 1's which is 12 o'clock that will enable preset which "SHOULD" set the 1's to a 1 instead of clearing it to 0. Now I can't find an IC chip that will do that. The 7493 only does BCD so 0-9 and thus not counting to 10.

My question is, is there any IC chips that counts like a 7490 but with a preset?

Now half of me decided that I'm just gonna build an asyncronous J-K Flip Flop Counter.

counter.JPG

I started with that but my question with that is why the hell does it start the count at 6?
When I run the design it will do 6-9 clears at 10 then goes back to 0-9 and runs normally. I don't get why that happens. Can anyone explain? Am I doing something wrong? I need it to do 0-9 from the get go because I think when I add the 10's digit and the preset it just goes haywire and I can't try to troubleshoot a more complicated schematic when its already doing bad at the beginning.

I appreciate any help thanks!