What Ladder Logic Is
Ladder logic is a graphical programming language for programmable logic controllers (PLCs). Programs look like electrical relay diagrams: contacts (inputs and conditions) on the left, coils (outputs) on the right, arranged in rungs. It is one of the languages defined by the IEC 61131-3 standard, alongside structured text, function block diagram and others.
Many tools are free in one of three senses: free to use in a browser, free to download and use for simulation, or free software that works with specific paid hardware. Knowing which kind you are looking at saves frustration.
Free Options at a Glance
| Type | Examples | Best for |
|---|---|---|
| Browser simulators | Open Rungs Studio, PLC Fiddle | Learning basics with no install |
| Open-source IDE | OpenPLC Editor | Learning and DIY hardware projects |
| Vendor software | AutomationDirect CLICK, Do-more Designer, Productivity Suite | Programming that vendor’s PLCs, with simulators in some cases |
| Multi-vendor platform | CODESYS | Wide hardware support, with licensing details to check |
| Microcontroller ladder tools | LDmicro | Hobby projects on small chips |
Browser-Based Simulators
Zero-install tools such as Open Rungs Studio and PLC Fiddle let you build rungs and watch inputs and outputs change in the page. They suit learning concepts like latching, timers and counters. They are not a route to real hardware, so treat them as practice areas. Features and availability can change, so check each site.
OpenPLC
OpenPLC is an open-source project with an editor that supports IEC 61131-3 languages, including ladder diagrams, and a runtime. The runtime can run on some boards and small computers such as a Raspberry Pi, and the editor includes simulation. This makes it popular for makers who want a real controller without buying industrial hardware. Supported hardware and features vary, so check the project documentation. It is suited to learning and hobby use; for production, consider the maturity and certifications of commercial products.
Vendor Tools
AutomationDirect offers free programming software for its own PLC lines, such as CLICK software, Do-more Designer and Productivity Suite. These have simulators or emulators in some cases, so you can test logic without a PLC. The catch is that the software mostly targets that vendor’s hardware, so skills transfer conceptually rather than file-for-file. Other manufacturers also provide free or trial engineering tools, but terms differ.
CODESYS
CODESYS is a widely used IEC 61131-3 development environment. The development system itself can generally be downloaded without a fee, and it includes a simulation mode. Running on actual controllers usually depends on the controller manufacturer’s runtime, and some runtimes require licenses. So whether CODESYS is “free” depends on the use case: free for learning and simulation, potentially paid when deploying to hardware. Check current license terms before relying on it.
Microcontroller-Oriented Tools
If your goal is ladder-style control on a hobby microcontroller, tools such as LDmicro compile ladder diagrams into code for supported chips. Support is limited and the project is niche, so read its documentation first. If you simply want Arduino-based control, ordinary C++ may be easier, as in our Arduino IoT projects guide.
How to Choose
- Just learning: start with a browser simulator or OpenPLC Editor’s simulation.
- Plan to buy a specific PLC: use that vendor’s free software, since you will need it anyway.
- Hobby or home automation: consider OpenPLC on supported hardware.
- Career-oriented: learn the concepts (scan cycle, timers, interlocks), and try more than one environment, since industries differ in which brand they use.
Is Ladder Logic Hard to Learn?
Many people with an electrical background find it approachable because it resembles relay schematics. The harder parts are the PLC scan cycle, state handling, timers and structuring larger programs. Starting with small exercises such as a start/stop motor latch, then timers and counters, is a common path.
Is CODESYS PLC Free? What Is a PLC in Software?
See the CODESYS section above for licensing. A PLC “in software” is a soft PLC: a program running on a PC or small computer that executes control logic like a hardware PLC. Simulators use the same idea so you can test without physical I/O.
Safety Note
Simulation is safe, but real machines are not. Software on a hobby setup should not be relied on for safety functions such as emergency stops. Those require proper safety-rated hardware and engineering practice.