Frequency Counter
:idea: This could depend on what parts you have available. One solution is to base your design on a simple decade counter with a store control (display held but keeps on counting), and reset control (resets counter to zero). You would then need to generate a 1Hz pulse fed in to a dual mono-stable (eg 4528 or 4538). The first mono-stable has it's output controlling the display store (normally held), the falling edge will trigger the second mono-stable whose output will reset the counter.
Basically this creates a 1 second window in which the pulses from your signal will be counted. At the end of this window the result is displayed and is proportional to the frequency of the signal being measured. This is then repeated for the next second.
Hope this helps? This will my first reply to a tech problem, so would welcome any feed back.
Trev