Change timer preset with button inputs

[atomic10]

Hi all. I am currently programming a Micrologix 1200 for a bike school and one of the requests that I have before me is to install push buttons to be able to speed up and slow down the timers controlling the traffic light cycles.

I figure the easiest way is to add 10 or subtact 10 seconds on the master timer preset with a press of the button, but as the rung remains true while the button is pressed, I get to a fault condition very quickly as it continues to add 10 until the button is release.

Sorry if this is an obvious question but my searching has found nothing; what is the simplest way to have it add/subtract 10 seconds with each button press?

 

[Steve Bailey]

Have each actuation of the pushbutton trigger a one-shot. Use the one-shot to control the addition/subtraction. That way you will have to release the pushbutton before adding/subtracting another ten seconds.

 

[atomic10]

*Facepalm* Much appreciated Steve. Have not used the one shot before so I was trying to use it in the ADD rung.. not the input where it should be.

 

[Eric Nelson]

Another option is to use the .DN bit of a self-resetting timer (or one of the S:4 clock bits) in place of the one-shot, to repeatedly add/subtract at a reasonable rate while the button is held. Saves having to press the button over and over when you want to make a large change.

If you do this, also add a short delay before initiating the auto-repeat function, similar to the key repeat delay on a computer keyboard.



-Eric

 

[Mickey]

I get to a fault condition very quickly

You also may want to consider checking for limits before writing the value to a timer preset. A "LIM" ( Limit Test) instruction works best for this.