PLC Programming: Ladder Logic for Beginners

Understand the PLC scan cycle and how a controller repeatedly reads inputs, executes ladder logic, and updates physical outputs.

Learn how to read a ladder logic rung using power rails, input conditions, contacts, output coils, and left-to-right logic flow.

Master essential PLC programming terms, including rungs, rails, contacts, coils, instructions, tags, addresses, bits, and scans.

Build and test your first ladder logic program by using a pushbutton input to control a lamp output in PLC Fiddle.

Learn how truth tables define every possible input combination and help you design predictable PLC control logic without guesswork.

Understand Normally Open and Normally Closed contacts and learn how PLC programs represent true, false, and NOT conditions.

Build AND logic with series contacts, OR logic with parallel branches, and exclusive OR logic using NO and NC contacts.

Apply Boolean ladder logic to control a motor using a Start button, guard sensor, and Emergency Stop condition.

Build the classic motor Start/Stop seal-in circuit and learn how a PLC output remains energized after a momentary Start button is released.

Compare standard output coils with Set and Reset instructions and understand when each memory method should be used.

Learn how rising-edge and falling-edge one-shots create a single PLC scan pulse when an input changes state.

Discover why controlling the same output coil from multiple rungs can create unexpected behaviour and how to structure the logic correctly.

Create, simulate, and test a complete Start/Stop motor-control circuit using a momentary pushbutton and seal-in contact.

Use a TON instruction to delay an output, monitor elapsed time, and understand timer presets, accumulated values, and Done bits.

Compare OFF-delay and retentive timers and learn how they delay shutdown or preserve accumulated time after a condition becomes false.

Learn how CTU, CTD, and CTUD instructions count events, track accumulated values, activate Done bits, and reset counts.

Combine PLC timers to create and simulate a repeating blinking-light oscillator while strengthening your understanding of timer sequencing.

Build a practical conveyor counter that detects passing products, counts them accurately, and activates an output when the target is reached.

Use EQU, NEQ, GRT, LES, GEQ, and LEQ comparisons to make PLC decisions based on temperatures, levels, speeds, and counts.

Perform arithmetic inside a PLC program using source values, destinations, and the ADD, SUB, MUL, and DIV instructions.

Use the MOV instruction to copy numerical values into setpoints, displays, timer presets, counter presets, and initialization tags.

Create a tank-level monitoring system with Low, Normal, and High indicators using comparison instructions and numerical range checks.

Understand how a finite state machine divides an automation sequence into clear operating states and prevents tangled ladder logic.

Represent machine states with internal PLC bits and use Set and Reset instructions to activate exactly one state at a time.

Build transition logic that moves a PLC-controlled machine safely from one state to the next when defined conditions are satisfied.

Design and simulate a complete traffic-light sequence using state bits, transition conditions, timers, and separate output rungs.

Learn why PLC fundamentals, engineering judgement, and safety knowledge must come before using AI-generated ladder logic.

Use Claude to transform a machine description into an organized PLC I/O list with clear inputs, outputs, internal bits, and tag names.

Prompt Claude to draft and explain ladder logic rung by rung, then translate and review the result in your chosen PLC simulator.

Use clear symptoms, expected behaviour, and rung descriptions to help Claude identify problems such as missing seal-ins and duplicate outputs.

Create effective PLC prompts using five ingredients: software context, automation goal, I/O list, operating constraints, and required answer format.