555Timer. - Here is Circuit Schematic and Project Simple RPM Counter using IC 555. RPM counters are used to measure Speed of Motors (AC/DC) or any Rotating Object. They measures and indicates current Rotating Speed of Motor. They are very essential in applications like Speed Control of Motors and close Loop Control System. Such industrial RPM counters are very accurate made up of microcontroller or microprocessor.
The circuit presented here is simple RPM counter without any microcontroller or microprocessor. It actually measures RPS – Revolutions per Second. By just multiplying RPS – Revolutions per Second with 60 we get RPM because
Revolutions per Minute = 60 × Revolutions per Seconds
It is built using simple Components like NE555, Decade Counter CD4026, and opto-interrupt Sensor MOC7811. It counts Motor Revolutions for 1 second and displays it on 2-digit Seven Segment Display. That is the RPS. To get the RPM we have to multiply this count with 60. Not only that, the time for which it Counts Revolutions can be set to 5 second or 10 second. So for slow RPM motors we can set different time. E.g. time is set for 5 second. So revolutions are counted for 5 second. Finally
RPM = 12 × Revolution Count
Similarly if time is set for 10 second
RPM = 6 × Revolution Count
Thus for higher RPM (>1000) motors, time is set for 1 second and for lower RPM Motor time is set for 5 second or 10 second.
The Original Article : "Simple RPM Counter using IC 555"