Last time we discussed the free virtual plc simulator called PLC Fiddle. It will enable you to create simple PLC ladder logic code within your browser. This is an ideal way in understanding PLC concepts for industrial automation. All of the basic PLC instructions that come with most plc units have been incorporated in this virtual PLC software.

http://accautomation.ca/plc-fiddle-online-editor-and-simulator-in-your-browser/

PLC Fiddle Video – This will demonstrate the basic functions of the PLC simulator.

Understanding and creating your own programmable logic controller programs in ladder can be fun. We will be starting with the basic gate logic circuits and convert these to ladder logic.

We will be looking at the AND, OR, NAND, NOR, EXOR and EXNOR logic circuits using PLC fiddle. This will get you involved in leaning and understanding PLC programming. Let’s get started.

**What are logic circuit gates?**

Logic circuits usually have two different input values to represent the Boolean values true (or 1) and false (or 0). Logic circuit gates have an output that is dependent on their inputs. We can draw logic gate charts to determine the status of each combination of input and output conditions.

Further information can be found at the following URL:

http://www.ee.surrey.ac.uk/Projects/CAL/digital-logic/gatesfunc/

Input 1 |
Input 2 |
Output |

0 | 0 | 0 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 1 |

The AND gate logic must have both Input 1 and Input 2 on in order for the output to be on. Everything else will keep the output off.

Your challenge is to use PLC fiddle to create an AND gate logic in ladder logic. Click the following URL to start the challenge.

https://www.plcfiddle.com/challenge/c70ba827-02d8-4899-a62c-ca63f4b98467

When you are finished the AND ladder logic, click the Check button to test the circuit.

**Watch on YouTube** : PLC Fiddle AND Gate Ladder Logic Challenge Solution

Input 1 |
Input 2 |
Output |

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 1 |

The OR gate logic must have either Input 1, Input 2 or both on in order to set the output on.

Your challenge is to use PLC fiddle to create an OR gate logic in ladder logic. Click the following URL to start the challenge.

https://www.plcfiddle.com/challenge/13f0f232-af8f-42c0-9113-a5644e0fe07d

When you are finished the OR ladder logic, click the Check button to test the circuit.

**Watch on YouTube** : PLC Fiddle OR Gate Ladder Logic Challenge Solution

Input 1 |
Input 2 |
Output |

0 | 0 | 1 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 0 |

NAND gate logic is just the opposite of the AND gate. The only time that the output is off is when both Input 1 and Input 2 are on.

Your challenge is to use PLC fiddle to create an NAND gate logic in ladder logic. Click the following URL to start the challenge.

https://www.plcfiddle.com/challenge/d17f32d5-a206-4051-8b9d-44aaa6faba8e

When you are finished the NAND ladder logic, click the Check button to test the circuit.

**Watch on YouTube** : PLC Fiddle NAND Gate Ladder Logic Challenge Solution

Input 1 |
Input 2 |
Output |

0 | 0 | 1 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 0 |

The NOR gate logic output is only on when both Input 1 and Input 2 are off.

Your challenge is to use PLC fiddle to create an NOR gate logic in ladder logic. Click the following URL to start the challenge.

https://www.plcfiddle.com/challenge/bea78e5c-dd08-49ec-911e-aee98d6056c4

When you are finished the NOR ladder logic, click the Check button to test the circuit.

**Watch on YouTube** : PLC Fiddle NOR Gate Ladder Logic Challenge Solution

Input 1 |
Input 2 |
Output |

0 | 0 | 0 |

0 | 1 | 1 |

1 | 0 | 1 |

1 | 1 | 0 |

Exclusive OR (EXOR) gate logic will only set the output on when Input 1 and Input 2 are at different states. The output only comes on when one input is on and the other input off.

Your challenge is to use PLC fiddle to create an EXOR gate logic in ladder logic. Click the following URL to start the challenge.

https://www.plcfiddle.com/challenge/fcb6a345-5a79-4dda-9e8b-efbb732d67bd

When you are finished the NOR ladder logic, click the Check button to test the circuit.

**Watch on YouTube** : PLC Fiddle EXOR Gate Ladder Logic Challenge Solution

Input 1 |
Input 2 |
Output |

0 | 0 | 1 |

0 | 1 | 0 |

1 | 0 | 0 |

1 | 1 | 1 |

Exclusive NOR (EXNOR) is just the opposite of EXOR. Input 1 and Input 2 must be the same state before the output will be turned on. Input 1 and Input 2 must both be on or both be off for the output to be on.

Your challenge is to use PLC fiddle to create an EXNOR gate logic in ladder logic. Click the following URL to start the challenge.

https://www.plcfiddle.com/challenge/cdeba4a9-b1c6-4558-a689-7dc0555662cd

When you are finished the EXNOR ladder logic, click the Check button to test the circuit.

**Watch on YouTube** : PLC Fiddle EXNOR Gate Ladder Logic Challenge Solution

These six basic gate ladder logic circuits were fun to solve using PLC Fiddle. It demonstrates the basic principles of programming without the investment of equipment. Next time we will use the same technique to do some Timer applications.

If you have any questions or need further information please contact me.

Thank you,

Garry

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