Push to ON PUSH to OFF PLC program using NO NC and Coil

is  Interview question that every PLC programmer came across in his
carrier.The Question is very tricky and shows the fundamentals (basic Ladder
Laws) and depth of candidates knowledge.

we are going to discuss PLC program for Push to ON device  and Push to Off
Device.But the trick is that we have to use  only Normally open(NO)
,Normally Close (NC) contacts ,and Coil as output only(No timer,Counter, OSR ).
In short there will be a single Push Button Input (X0) , and one Output (Y0).
When user press Push button for 1st time output will be ON ,when user Presses
Push Button for 2nd time output will be OFF. This is also called as “Push
to On Push to Off ” logic.Analogy can be provided with “TV” on
and off Push Button. 

  We Can Break Sequence Like This :
1) Push Button Pressed (X0) ==> Output (Y0)On
2)Push Button Released (X0)==> Output (Y0) Latched
3)Push Button Pressed (X0)==> Output (Y0 )Off
4)Push Button Released (X0)==> Output (Y0) Off
Remember you can write PLC program in number of ways 
  •  Using
    only NO,NC,Coil only
  • Using
  • Using
    Pulse Instruction
  • Using OSR
    (Rising Edge ,Falling Edge) Instruction
 below program is using NO,NC,Coil

Note:Do not Replace M0 with Y0

Below Program is using Counter instruction

Below Program is using PLS instruction

Question asked on this are related to Scan time and rung interchange etc.

Check Video Demonstration of Above Program

Leave a Reply