In this design we use AT89S52 microcontroller to build inexpensive revs-per-minute meter. This meter can measure speed in the range of 1 to 9999 rev/min. This design was originally developed to measure the speed of brushless motors, but it can use for any application where the speed is in above mentioned range. In the given design input pulses are generated using Allegro A1203 Hall-effect bipolar switch and it can be replaced with any other Hall-effect sensor or IR detector.

Current version of RPM counter is based on Atmel’s AT89S52 8bit MCU and control software is developed using MikroC 8051 compiler.

At the time of implementation and testing we use Allegro A1203, A3517 and A3056 (for gear-tooth sensor operations) Hall-effect bipolar switches with this system and all these sensors produce excellent results with it.


Construct the circuit on a common PCB and house it in a small plastic casing. In this design we does not include schematic of the power supply unit (PSU) and it may be any +5V – 200mA (or high current) power supply unit.

For the seven-segment display use four separate seven segment display modules or parallel wired seven-segment display module (which was available in satellite decoders and VCR’s)

Seven Segment Connectivity

When setting up the Hall-effect sensor user need to consider about the effectiveness of magnetic flux lines to the sensor. Hall switches have an active area that is closer to one face of the package (for most of the Allegro Hall-effect sensors it is the branded face). To operate the switch, the magnetic flux lines must be perpendicular to this surface of the package, and must have the correct polarity. To get more information about Hall-effect sensor installations, please refer the Allegro MicroSystems - Application Note 27701 (Hall-Effect IC Applications Guide)

Project Related Downloads

Complete Circuit Diagram and Source Codes of RPM Counter


AT89S52 8bit MCU datasheet
Allegro A1203 Hall-effect bipolar switch datasheet
Allegro MicroSystems - AN27701 - Hall-Effect IC Applications Guide