How does a digital tachometer work using 555 timer op to IC7490-7492-7492 another 555 timer to three IC74160?

A digital tachometer can be constructed using a 555 timer configured in astable mode to generate a pulse train proportional to the input frequency from a rotating shaft. This pulse train is fed into a counter IC (like the 7490 or 7492), which counts the number of pulses over a specific time interval. The output from the counter can then be connected to a second 555 timer, configured in monostable mode, to produce a stable output pulse that can reset the count at regular intervals, allowing the connected IC74160 counters to display the speed in a human-readable format. By properly calibrating the system, the displayed count can be translated into revolutions per minute (RPM).