Sequential Light control using Schnieder M340 PLC

In many decorative and industrial applications, multiple lights are used to create visual effects or indicate process status. Controlling these lights manually is inefficient, inconsistent, and prone to human error. A PLC‑based sequential light control system automates this process, ensuring precise timing, repeatability, and flexibility.

This system turns ON lights one after another in a defined sequence, maintains them for a set duration, and then turns them OFF in the same or reverse order. Such automation is widely used in advertisement displays, event lighting, runway indicators, and process signalling systems.

Schematic:

The system consists of:

- PLC

- 6 Output

- Start Push Button (Input)

- Stop Push Button (Input)

- Timer blocks inside PLC

Solution

A PLC-based sequential light system is designed using ladder logic. When the Start button is pressed, the lights turn ON one by one with a time delay between each light. After all lights are ON, they either turn OFF sequentially or the cycle repeats. The Stop button stops the process anytime.

 

PLC Program (Ladder Logic):

 

Explanation:

Initially, when the Start push button is pressed, the system is latched using an internal memory bit (M0). This latch ensures continuous operation until the Stop button is pressed. Once latched, the first timer (T1) is activated.

After a delay of 5 seconds, Timer T1 completes its cycle and turns ON Light 1 (L1). The activation of L1 triggers the next timer (T2), which after another 5‑second delay turns ON Light 2 (L2). This sequential process continues — L2 activates T3, L3 activates T4, and so on — resulting in a smooth, timed lighting sequence.

The Stop push button is used to break the latch (reset M0), immediately halting the entire process and turning all lights OFF.

System Highlights

Sequential Operation: Lights turn ON one after another with precise timing.

Programmable Delay: Timing between lights can be easily modified in the PLC program.

Safe Control: The latch ensures controlled operation and immediate stop when required.

Flexible Design: Sequence can be reversed or looped continuously.

Applications

Decorative lighting systems for events and exhibitions

Advertisement and display boards

Runway or pathway lighting

Industrial indication and signalling systems

Advantages

Flexibility: Timing and sequence can be adjusted without hardware changes.

Reliability: PLC ensures consistent and error‑free operation.

Ease of Modification: Logic can be updated quickly for different patterns.

Educational Value: Demonstrates timers, sequencing, and ladder logic fundamentals in PLC programming.