With two IC's and a 7-segments LED-display one can build a decimal counter that
counts pulses from 0 to 9. A possible application of this is counting the number
of products that pass a certain point of a production line. The counter can be
cascaded to count any large decimal number.
The total diagram consists of a BCD-counter, a 7-segments-decoder and a
The counter is in a C-MOS IC of the type 4518. It contains two 10-counters, a
and b. Each counts binary from 0000 to 1001 and then returns to 0000. We only
use one of them; b.
The 7-segments decoder is in the CMOS IC 4543. This IC turns a binary number of
0000 to 1001 into seven binary outputs, in such a way that on the display they
show the numbers that can be seen on the picture.
The LED-display HDN1131 (print the data sheets) needs resistors R to limit
the current in each diode. For this type, that should be about 2 mA.