Flashing light with only one timer

winz33 · Dec 7, 2009

How do you have a light flash every two seconds (on 2s then off 2s) with only one timer? Thanks.

bernie_carlton · Dec 7, 2009

This sounds like a student question so I'll answer with questions to cause you to think your way through this.

Have you learned about timers and their respective parts (Preset, Accumulated or Current Value)?

Have you learned anything about using numeric comparisons in ladder logic?

Try those for hints.

PhilipD · Dec 7, 2009

winz33,

Are you required to use a timer?

Steve Bailey · Dec 7, 2009

If your teacher hasn't introduced comparison instructions yet, how about a self-resetting two second timer and a flip-flop?

jrwb4gbm · Dec 7, 2009

bernie carlton's method is better than mine but here are some hints for a different method that doesn't use numeric comparison instructions. Search how a flip-flop is programmed in ladder logic. Here's a link to a flip-flop explanation:
http://www.patchn.com/index.php?option=com_content&task=view&id=60&Itemid=74
Use that and a logic rung with a free running (Self-resetting) timer.Use that timer to trigger the flip-flop.

Edit: Steve Bailey types faster than me.

Mechtrician · Dec 7, 2009

Here is an example in RSLogix 500.

TConnolly · Dec 7, 2009

Consider the binary pattern of the value stored in the accumulator of a one second time base timer.

T = 0 = 000000
T = 1 = 000001
T = 2 = 000010
T = 3 = 000011
T = 4 = 000100
T = 5 = 000101
T = 6 = 000110
T = 7 = 000111
T = 8 = 001000

The light will be off for T= 0 and 1. It will be on for T= 2 and 3. Off for T=4 and 5, on for T=6 and 7. Now look carefully at the binary values. Do you see a pattern that you can use?

Assuming you are using an AB PLC, you can address any bit in the timer acc. T4:0.ACC/0 refers to the first bit. T4:0.ACC/1 refers to the second bit, etc.

T4:0.ACC/1
----] [-----

mark godby · May 9, 2011

T4:0.ACC/1 works great! Thanks guys
If you put an input before T4:0/DN you can control the logic.
Im really new

Eugen · May 9, 2011

Based on Bernie and Alaric explanation. How about a traffic light programm with only one timmer.

MTPLCUSER · Feb 10, 2015

In the logic above, how does B3:0/1 continue to blink after the timer is done?

bernie_carlton · Feb 10, 2015

In the enable line for the timer is its own 'done' (/DN) bit. It finishing the time will turn this ON which will reset the timer. When reset the 'done' bit will turn back off and the timer begins again.

Flashing light with only one timer

winz33

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bernie_carlton

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PhilipD

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Steve Bailey

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jrwb4gbm

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Mechtrician

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TConnolly

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mark godby

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MTPLCUSER

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bernie_carlton

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