This is a clock powered by mains via 12vac transformer, which also supplies the 60Hz frequency for time keeping. It is in military time format and has momentary switches for setting the current time, resetting the seconds count and a SPST for activating SET mode, indicated by a red LED. It uses 16 bit counter IC’s, binary to 7 segment converters and 7 segment LED displays. Counter resets are done with AND logic IC’s. LED’s are used here as blocking diodes for adjustment signals in simulation because I can set the Vf to 100mV, a low Vf Schottky diode should be used as blocking diodes.
Rectified ac is sent to a comparator which outputs a high signal when the AC crosses a 2.5V reference, supplying a 30Hz square wave. This is sent to a counter, which counts to 15 and resets. This reset signal is also sent to another counter IC’s input, which counts to two and resets. Thus a single pulse is supplied every second. This is sent to a counter which displays the seconds counted, forwarding and resetting on the 10th. The next counter counts and displays tens of seconds, forwarding and resetting on the 6th. The following counter displays minutes, counting out 9 minute pulses and displayed them on a 7 segment, forwarding and clearing on the 10th. The following counter counts 5 tens of minutes and displays them, resetting and forwarding on the 6th, to the hour counter. The hour counter displays the hour pulses, forwarding and clearing on the 10th hour count. The final display counts out tens of hours, clearing both the ten and single hours on the 24th hour.
