Fig. 2 - synchronisation circuit

Fig. 3 - 1's & 10's seconds counter

Fig. 4 - LED drivers

The vintage circuit MM5316 (National Semiconductors) is known from 1970 to 1980. It provides a four-digit, non-multiplexed clock output for different displays. The circuit is clocked by a 50 Hz or 60 Hz clock source and also has 1 second (1 Hz) output (pin 39).

The 4026 counters must count to 60 and be synchronized with minutes. Fig. 2 shows the synchronization circuit is composed of three gates CD4027. The gates are connected to the outputs MINUTES.A (pin 18 of MM5316) and MINUTES.E (pin 20 of MM5316) and generate a RESET signal for the counters 4026.

With a few CMOS 4000 circuits, an upgrade is performed for seconds. Fig. 3 shows a counter for seconds and 10 seconds. The circuit has two CD4026 counters with 7-segment outputs. Both counters are clocked by the 1 Hz (1 s) MM5316 output.

Since counters 4026 can not control LED displays directly, external power drivers are required. Fig. 4 shows a possible solution of two ULN2004.