Free PLC Simulator
Edit a rung, click Run, then press Switch to see the Lamp coil turn on. No installation or account required.
Program blocks 8
Task / brief
Goal
Make the Lamp output follow the Switch input exactly.
Inputs / outputs
Hints
Main [LAD]Modified
Properties coil · 1 path
PLC tags / I/O table (2/64)
%I Input · %Q Output · %M Internal bit / byte.bit (0–7)
Address naming rules
| Area | Meaning | Example |
|---|---|---|
%I | Input | %I0.0, %I0.1 |
%Q | Output | %Q0.0, %Q1.0 |
%M | Internal bit | %M0.0, %M0.1 |
- Format: %areaByte.bit. Bytes: 0–65535; bits: 0–7. After %I0.7 comes %I1.0, not %I0.8.
- Enter I1.2 or i1.2 to normalize to %I1.2. Addresses must match the direction and be unique.
- Symbol names appear above ladder elements; addresses appear below. All contacts bound to a variable share its address.
- These BOOL addresses are for simulation. The byte limit does not describe every physical CPU.
| Symbol | Address | Direction | Type | Initial | Live | Comment | |
|---|---|---|---|---|---|---|---|
| Switch | BOOL | ||||||
| Lamp | BOOL |
Addresses are saved with the project. Existing tags keep their addresses when another tag is deleted. Exercise IDs keep their physical role.
Simulation / live I/O
Device feedback
StoppedVariable table
2| Name | Address | Value | Control |
|---|---|---|---|
| Switch | %I0.0 | 0 | |
| Lamp | %Q0.0 | 0 |
Diagnostics / verification3 cases
Test 1 of 3
Entire suite · isolated engines · results clear on edit
Test 1: Lamp is off initially
Click Run test to evaluate the entire suite.
Ladder logic example: one contact and one coil
The default rung connects a normally open Switch contact (%I0.0) to a Lamp coil (%Q0.0). While Run is active, holding Switch makes the rung conduct and turns the coil on; releasing it turns the coil off. Select a symbol to edit it, or use Start blank to draw your own rung.
Each walkthrough explains the reference program, common mistakes and how to verify the result.
Want to experiment with latching coils, off-delay timers or down counters? Open LadderLab, our free-form ladder logic editor, with seven ready-to-run examples.
Eight ladder logic examples
- Lamp FollowInput · Coil · Normally-open contact
- Two-Button ANDSeries contacts · AND logic
- Either-Button ORParallel branches · OR logic
- Motor Start/StopSelf-latch · Stop priority · Normally-closed contact
- Delayed StartTON timer · Preset time · Edge / interrupt behavior
- Batch CounterCTU counter · Rising edge only · Reset priority
- Traffic LightSequencing · Timers · Interlock (mutual exclusion)
- Tank Level ControlHysteresis · Self-latch · Two thresholds
New to ladder diagrams? Start with ladder logic basics. Simulation is for learning, not controlling real machinery.