GolamMostafa:
If you want to measure the speeds of the the rotating bodies, you may also adopt the following hardware scheme. In this scheme, 2 counters will be accumulating the pulses coming from 2 sensors; normalize the counts and then show the RPMs (RPM1, RPM2) on the LCD. The 3rd sensor will deliver its output to the UNO via interrupt; UNO will be counting the incoming pulses; normalize these counts and show RPM3 on the LCD. This scheme will also give you Real Time processing of the events.
Ok this seems to be a nice idea to work on. But I'm new to using counters. Is there any difference in hardware or just some changes in prgram?