Closed Loop Motor Control System (QNX RTOS)

A real-time, multithreaded embedded C application running on QNX RTOS that implements a deterministic closed-loop control system. The system reads feedback from a Hall sensor, processes it through a PID controller, and drives a DC motor via PWM using GPIO on Raspberry Pi 4.

Features

Real-time closed-loop control using feedback PID controller (Proportional + Integral + Derivative) Deterministic execution with 10ms fixed control loop Multithreaded design (Sensor, Controller, Actuator) Priority-based scheduling using SCHED_RR Direction control (Forward / Reverse / Stop) LED visualization for system state CSV logging for analysis (/tmp/log.csv) Safe shutdown with GPIO reset on termination Mutex-based shared memory communication

Hardware Requirements

Raspberry Pi 4 QNX Neutrino RTOS (7.x / 8.x) L298N Motor Driver DC Motor LM393 Hall Effect Sensor Small Magnet (attached to motor shaft) LEDs (5x for status indication) Jumper wires + Power supply

GPIO Configuration

Component GPIO Pin PWM Output GPIO 13 Motor IN1 GPIO 17 Motor IN2 GPIO 27 Hall Sensor GPIO 22 Green LED GPIO 5 Red LED GPIO 6 Blue LED GPIO 12 Yellow LED GPIO 16 White LED GPIO 20

System Architecture

Control Loop Flow Sensor → Controller → Actuator → Sensor (feedback loop) Threads & Scheduling Task Priority Role Sensor Task Medium (15) Reads encoder (Hall sensor) Controller Task High (20) Executes PID algorithm Actuator Task Medium (15) Drives motor & LEDs

✔ Scheduling Policy: SCHED_RR ✔ Loop Period: 10ms (deterministic)

Control Logic

Setpoint (SP): Target encoder count Feedback: Hall sensor pulse count Error: SP - Encoder PID Equation: Output = KP * error + KI * integral + KD * derivative

LED Indication

LED Condition Green Forward Red Reverse Blue Low speed Yellow Medium speed White High speed

Logging

Data is logged to: /tmp/log.csv

Format:

Setpoint,Encoder,Speed,Direction,Green,Red,Blue,Yellow,White

Build Instructions

We are Using QNX Momentics IDE Import project clean Project

Build

Terminal Build: make clean make

Run Instructions

./closed_loop_contol_system

Stop Program (IMPORTANT)

CTRL + C

✔ Motor stops immediately ✔ LEDs turn OFF ✔ Cleanup ensures safe shutdown

Known Limitation

Uses Hall sensor (single channel) Cannot detect direction inherently Reverse control is approximated using software logic