VERSION 1.0 · OPENPLC LOGIC & SIMULATION

Car Parking Lot Barrier Controller

A compact IEC 61131-3 control project that tracks parking occupancy with a CTUD counter, automatically permits vehicle entry when capacity is available, and blocks the barrier when the lot is full.

View Test Results Explore PLC Logic

CTUD Up/Down Counter

10 Simulated Capacity

FBD IEC 61131-3

Completed OpenPLC function block diagram for the parking barrier controller

ParkingController Function Block Diagram

PROJECT OVERVIEW

Automated capacity control for a small parking lot

The controller counts arriving and departing vehicles, evaluates available capacity, and controls the entry barrier through a simple, testable Function Block Diagram.

Occupancy Tracking

The CTUD block increments for entries and decrements for exits while maintaining the current vehicle count.

Barrier Permission

The barrier opens only when an entry request is present and the current count is below maximum capacity.

Full-Lot Protection

When the preset value is reached, the full-lot output becomes active and blocks additional entry commands.

Dual Test Inputs

Both simulated sensor inputs and HMI command inputs were validated for entry, exit, and reset operation.

CONTROL REQUIREMENTS

Core operating sequence

Detect an entry request

An entry sensor or HMI command creates a rising-edge signal for the CTUD count-up input.

Check available capacity

The barrier is permitted only while the lot-full condition remains false.

Track departures

An exit sensor or HMI command pulses the CTUD count-down input and reduces the occupancy count.

Reset the simulation

The reset path clears the CTUD current value and returns the system to the empty-lot condition.

PLC LOGIC

Function Block Diagram and variable configuration

The program combines OR logic for sensor and HMI requests, a CTUD function block for occupancy, and AND/NOT logic for barrier permission.

Completed parking controller function block diagram — Control Logic **Complete Function Block Diagram**

OpenPLC parking controller variable table — Configuration **Variable Table and Data Types**

BARRIER CONDITION

Barrier_Open = Entry_Request AND NOT Lot_Full

Entry_Request is generated from either the physical-style entry sensor or the HMI simulation input. The lot-full signal overrides the request and keeps the barrier closed.

SIMULATION RESULTS

Validated operating scenarios

Each test was performed in the OpenPLC Online debugger using Boolean pulses and live monitoring of the CTUD outputs.

Empty parking lot debugger test — Initial State **Empty Lot Test**
Car count is zero, the empty indicator is active, and the barrier remains closed.

Entry sensor simulation test — Sensor Scenario **Entry Sensor Test**
A rising-edge sensor pulse opens the barrier and increments the vehicle count.

Entry HMI simulation test — HMI Scenario **Entry HMI Test**
The HMI request follows the same OR path and produces the same validated entry behavior.

Exit sensor simulation test — Sensor Scenario **Exit Sensor Test**
An exit pulse drives the CTUD count-down input and reduces occupancy by one.

Exit HMI simulation test — HMI Scenario **Exit HMI Test**
The HMI exit command is validated independently from the simulated physical sensor input.

Full parking lot debugger test — Capacity Protection **Full Lot Test**
At maximum capacity, Lot_Full becomes true and the barrier permission is removed.

Parking controller reset test — Recovery **Reset Test**
The reset command returns the vehicle count to zero and restores the empty-lot state.

Successful OpenPLC compile and runtime log — Build Verification **Successful Compile and Run**
The final build completed successfully and the PLC program entered the running state.

I/O AND VARIABLES

Key project signals

Variable	Type	Purpose	Version 1 Role
`Entry_Sensor`	BOOL	Simulated entrance detector	CTUD count-up request
`Exit_Sensor`	BOOL	Simulated exit detector	CTUD count-down request
`Entry_HMI`	BOOL	Future HMI entry command	Validated through OR logic
`Exit_HMI`	BOOL	Future HMI exit command	Validated through OR logic
`Car_Count`	INT	Current parking occupancy	CTUD current value
`Lot_Full`	BOOL	Capacity reached indicator	Blocks entry barrier
`Barrier_Open`	BOOL	Entrance barrier command	Entry request AND available space

VERSION ROADMAP

From PLC simulation to a complete HMI system

Released v1.0.0

OpenPLC Logic and Simulation

CTUD occupancy tracking
Entry and exit request handling
Capacity interlock
Barrier control logic
Debugger validation
GitHub Pages case study

Planned v2.0.0

HMI and Modbus TCP Integration

CODESYS or FUXA visualization
Modbus TCP communications
Live occupancy and capacity display
Animated barrier status
Alarm and event indicators
Occupancy trend visualization

PROJECT REPOSITORY

Explore the source files and project documentation

Version 1 documents the control strategy, OpenPLC implementation, debugger validation, screenshots, and deployment notes for the parking barrier controller.

View GitHub Profile Back to Top