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.