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OK, lets start with 1s signal.
Easiest way will be 2_Nand (7400, ...) gates and 32768Hz cristal quarz. Next you will need 15-stage /2 devider which you can do with 4 x 7493.
The main counter may be built with 74192 counters: units modulo 10, tens-of-seconds modulo 6, minutes modulo 10, tens-of-minutes modulo 6 ....
These counters have ABCD outputs which will feed 7447 7-segment LED drivers. The outputs of 7447 will be connected trough resistors (values determined from displays data sheets) to 7-segment LED common anode.
This is very, very general description. If you need more details let us know...
Hi Everybody
Dear Chipper those resistors only limit the current flow through 7-Seg's LEDs.
Usually, LEDs can generate visible light with 10-15 mA current and 1.5-2 V voltage across them. Suppose the supply volatge is 5 V. You can calculate the value of these resistors yourself.
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