RPM Display and Speed Control of a Brushless DC Motor Using 8051 Microcontroller
DOI:
https://doi.org/10.67308/irjist.100Keywords:
Closed-Loop Speed Control, Pulse Width Modulation (PWM), RPM Measurement, Infrared (IR) Sensor, Embedded Control System., Brushless DC (BLDC) Motor, 8051 MicrocontrollerAbstract
Brushless DC (BLDC) motors are widely used in cooling fans, pumps, robots, medical devices, and electric vehicles because of their efficiency and long service life. However, their shaft speed can vary with supply voltage and mechanical load. Therefore, a practical drive system requires both a speed set point and a means of monitoring the actual shaft speed. This paper describes a low-cost closed-loop speed controller and RPM indicator based on an 8051-family microcontroller. The user selects the reference speed using UP/DOWN push buttons. The microcontroller generates a PWM signal in software using its on-chip timer, which drives the motor through a switching power stage. An infrared (IR) emitter–photodiode pair detects one pulse per revolution from a reflective marker on the shaft. These pulses are counted over a fixed gate time to determine the speed in RPM. The measured speed is compared with the reference speed, and the PWM duty cycle is adjusted after each gate interval. Both reference and measured speeds are displayed on a 16 × 2 LCD. The prototype was tested over a speed range of 500–2500 RPM, with the measured speed remaining within 2.0–3.0% of the set value. The paper presents the design details, measurement procedure, repeated-reading protocol, and error analysis.
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Copyright (c) 2026 Ankita Sasane, Vaishnavi Dhakare, Sahil Sarang, Prajwal Bake, Siddharth Bhorge, Rahul Pol (Author)
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