Single Push Button Start/Stop Ladder Logic Diagram using Siemens TIA Portal

Many times it is asked to develop a ladder logic turn ON and OFF a lamp using a single push button.

A single push button in ladder logic is a simple switch mechanism used to control some aspects of a machine. When a push button is pressed and released, the process turns ON with the help of latching and again the same push button is pressed and released, the process turns OFF.

This is the most widely used PLC Ladder Logic example.

Table of Contents

What is Ladder Logic Diagram?

Ladder Logic is a programming language is to programs a Programmable Logic Controller. Ladder Logic is used to develop a program for a PLC.

Ladder Logic Diagram also known as Ladder Diagram (LD) is the most common programming language used to program PLCs. It is a graphical language that shows a logical relationship between inputs and outputs as like they are relays.

Single Push Button ON/OFF Ladder Logic Diagram

Single Push Button START/STOP Ladder Logic Diagram

Siemens TIA Portal v15.1 software is used to program Siemens PLCs. In this post, we have used S7-1500 series PLC which has 16 digital inputs, 16 digital outputs, 5 analog inputs, and 2 analog outputs.

For programming a single push button ON/OFF function, we require only one input. One output is used to show the result on the PLC trainer. In real-time, if you are not needed to use any output, one can use a Memory tag instead.

Below is the list of PLC tags used along with their address.

I0.0 – Push Button ON/OFF (Input)

Q0.0 – Desired Output (Output)

M0.0 – ON Memory (Memory)

M0.1 – OFF Memory (Memory)

The Push Button used in this example is normally open (N.O.).

Single Push Button ON/OFF Ladder Logic Program uses only 3 rungs to give an output. To explain the program, it is divided into 3 networks. Network 1 explains the logic when we press Push Button for the first time i.e. to start the cycle. Network 2 explains the logic when we again press the Push Button to stop the cycle. And network 3 explains Single Push Button ON/OFF logic.

Network 1:

When Push Button is pressed, N.O. The Push Button gets closed to turn on the ON Memory M0.0. Please note that, as we are pressing the Push Button for the first time OFF Memory must be normally closed (N.C) in order to turn on M0.0.

And when the Push Button is pressed for the second time, M0.1 turns ON (explained in network 2). As M0.1 turns ON, N.C. M0.1 in network 1 turns OFF cutting the power of M0.0 and thus, M0.0 turns OFF.

Network 2:

On pressing the Push Button for the first time, M0.0 which is N.C in network 2 will turn N.O., Q0.0 will turn N.C. and M0.1 will not turn ON.

For the next push button press, M0.0 will turn N.C and M0.1 will turn ON. As M0.1 turns on it will cut off the power supply of the output Q0.0 explained in network 3 and the system turns OFF.

Network 3:

After pressing the push button, M0.0 turns ON as explained in network 1. In network 3, M0.1 is N.C. and hence M0.0 ON condition turns ON the Output Q0.0. Note, that, this output must be latched in order to keep the system running.

If we again press the push button, M0.0 turns to N.O. cutting the power supply to the output. And this turns OFF the system.

Now, we will see Single Push Button ON/OFF Ladder Logic Diagram in one network only.

Single Push Button ON/OFF Ladder Logic Diagram

If there isn’t any output to turn on like for example Conveyor Motor, one can use PLC Memory Tag which is not used in the above program like M0.2, M0.3, etc. to turn ON/OFF the system.