Basically a counter circuit activates a sequence of signals one at a time, through a clock pulse,
which is automatically or manually sent.
Counter circuits can be digital or relay based.
This is a four stages relay logic counter. In this case the clock signal is automatically sent
by the relays K and K1. Once you supply the circuit the clock relays (K and K1) start working
in astable mode, but you have to press the button in order to trigger the cycle. Of course a relay
based circuit works fine with a clock time of one second or more.
This one is a 24 stages counter, made by three CD4017 integrated circuits. The clock signal
is sent by a NE555 timer. Relay contacts (RS1, RS2, RS3) are also used to control clock and
Digital counter circuits (also called shift registers) are often based on the CD4017 or similar
components. However a
shift register can be made with basic components, such as logic gates.