Kenneth Finnegan who shared his DIY Binary Clock Build with us has made another clock. This time it’s a Digital TTL Clock. This design brings back memories of college when I had to design a mock photocopier circuit that allowed the entry of number of copies and decremented the number till it was down to zero. I also used 7 segment displays and the same driver chip. I have to admit that I’m sure glad there are more powerful ways to solve the problem these days. He has a schematic that shows how he generates his 1 Hz clock pulse from a 32.768 KHz crystal oscillator. Watch the video below for a full walkthrough of the circuit.
“Once divided down to 1Hz, the rest of the clock is simply a matter of counting seconds, minutes, and hours, and displaying them. The seconds stage consists of nothing more than a 74160 divide-by-10 and a 7493 wired as a divide-by-6, which feed a pair of 7447 BCD to seven segment decoders for display. The 7493 normally divides by 16, but I used a 7408 AND gate between the 2 and 4 output lines, such that when the counter (which signifies the tens of seconds digit) reaches six, the AND gate goes high, resets the counter, and pulses the carry line to the minutes stage.”