How to works:
IC1 is dual BCD decade up counter. IC2 and IC3 is BCD
to the dual digit display. The input signal will transmitted to pin 1
of IC1. The internal circuit of IC1 will be dual decade counter.
This signal is fed to 1st decade counter circuit. When the 1st
decade counter circuit to count ten point will transmitted the
signal to the 2nd decade counter circuit through pin 6 of IC1.
After the 2nd decade counter circuit to count ten. At "OUT"
point is used to increase the digit. Then it will be transmitted to
other point. The pin 7 and pin 15 of IC1 is connected to reset the
circuit. SW2 check the counting. The circuit can supply the
voltage at 12VDC. TR1 and TR2 work as a buffer.