7segment display clock

[Gabmen]

Hi all, am desining a 7-segment LED clock using 4017 as the couter and 4511 as BCD 7-segment driver. The clock is working just fine with the british method of 24:00 hours but i want it to count 12:00 hours and jump back to 01:00 instead of 24:00. No microcontrollers. I will appreciate if any one could help me out.

 

[HMS1021]

Just a 4017 decade Johnson counter would roll over at 99, not 59 for minutes and 24 for hours. So there must be additional circuitry to cause the 59 and 24 roll over. Once you understand this circuitry it will be easy to change it to the 12 hour format.