PLC Programming for Blinking Indicator Lights


Blinking indicator lights are used quite extensively in the industry. Design a circuit in which two lights are flashed alternately every 2 seconds. After blinking 10 times it automatically turns off.

PLC Programming for Blinking Indicator Lights

As per the given problem, we need a blinker that blinks after every two seconds and after blinking for ten times it should stop automatically.


It contains a simple holding circuit, in which an NO is connected in parallel to the start input, which in combination acts as a holding circuit.

The output M0.0 (Timer supply) is connected in series with the NC contact which is used for breaking the circuit.

PLC Programming for Blinking Indicator Light


M0.0 is used as a supply for the timer in network-2. It has two timers connected in parallel

Along with interlocks so that logic works accordingly.

The network consists of a timer TP (Pulse timer) with a preset time of 2 seconds which is used to keep the output Q0.0 high for 2 seconds.

Flashing Light PLC Ladder logic

TON is another timer connected in parallel with TP with NC connected having an address of Q0.0 which helps us to activate the TON.

The output from TON ie. M0.1 is given as NC in series with NO of M0.0 so both the timer gets reset accordingly. Now combining Network-1 and 2 our blinker is ready.


To count the number of blinks we need a counter. Each time the value of the counter is incremented by one.

The blinking count is dependent on the Q0.0 which has been given as input to the counter.

PLC Blinker Logic

The counter is given a preset of 10 so that on the tenth blink the blinker stops. To do so we have given an NC on Counters-output in Network-2.

The flashing lights PLC program example from our Siemens PLC course.

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  1. I really appreciate this course. But i have a question. The solution above only has one OP for one LED. The problem statement was to have two LEDs that alternated for 2 Sec each, and then turned off after 10 pulses.

  2. I hit enter too quickly, my question is do i need another complete NW like NW2 to make the second LED flash, but use NC contact of %Q0.0 to ensure they alternate?