ON Time Delay in a circuit

Discussion in 'General Electronics Chat' started by jothom, Jul 19, 2018.

  1. jothom

    Thread Starter New Member

    Jul 19, 2018
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    hi all,

    a quick question about a ON delay in a circuit,

    i have an circuit where i require 2 outputs from 1 switch, so a DPDT Rocker switch will do the job, that switch basically controls 2 mini circuits one of the circuits needs to be powered first as its a brake release , the other circuit needs to be powered about 0.5 - 1 second after because its a drive command, the controller will throw up an error and not move if the signals are read at the same time this is why i need a delay in the drive command circuit.

    its only a 5v line that is stepped down to about 1v, it doesnt matter if its before of after the step down.
    the price is an issue because if it costs more than $5 to do then the job would not be worth it.

    i have some cheap control boards that will do the job on the way in the mail but im just wondering if there is calculations and components i can use to make a small delay using, resistors, capacitors and transistors.

    any advice will be helpful
    thanks
     
  2. Xavier Pacheco Paulino

    Active Member

    Oct 21, 2015
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    You can try the popular 555. The time is adjusted by setting the proper RC network. t= 1.1*R*C. Note that the formula provides an estimated time, which also depends on the quality of the components.

    [​IMG]
     
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  3. Xavier Pacheco Paulino

    Active Member

    Oct 21, 2015
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    It would be useful if you post the circuit that you want to delay at turn on. So we can see how the 555 can be connected to that circuit, because in the schematic above, you can see that the LED is the load, or the delayed element.
     
  4. jothom

    Thread Starter New Member

    Jul 19, 2018
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    i can look at getting that done, i have brought a 555 board im just waiting on it in the mail, i will get a drawing made and post it when i get chance, thanks for the help
     
  5. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Is there a reason why you don't capitalize
    Time delay using 555 timer:
    upload_2018-7-19_9-8-21.png
    upload_2018-7-19_9-8-35.png

    Note: The pronoun 'I' is capitalized. Not doing that, as you have done repeatedly, distracts from what you're trying to convey because many, myself included, will be distracted by your misspelling. We also capitalize the first word in a sentence.
     
  6. ebeowulf17

    AAC Fanatic!

    Aug 12, 2014
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  7. crutschow

    Expert

    Mar 14, 2008
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    Does this simple circuit do what you want?

    C2 suppress a short output glitch at the start of the delay. If that's not a problem in your circuit then you don't need C2.

    V1 [V(in)] simulates the output from your rocker switch.

    upload_2018-7-19_11-5-0.png
     
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  8. danadak

    Distinguished Member

    Mar 10, 2018
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    is there a worst case max rise time associated with the inputs
    of the module you are driving ?

    A slow rise time, especially one that hovers in the threshold range of
    a logic input, can cause some real problems, false triggering, excessive
    power dissipation......

    Regards, Dana.
     
  9. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    Didn't notice it until you said something.

    Since it's a "Command" line, a simple buffer and an RC circuit would probably be able to give you plenty of time delay. The command from the switch feeds through a resistor into a capacitor and the input of a buffer. When you switch on the resistor prevents the cap from going to full voltage in an instant (theoretically) (don't nobody bash me for saying caps go to full voltage instantly - we all know they don't. But for the sake of argument). The cap slowly charges up through the resistor. When the voltage reaches the threshold of the buffer it switches on and your command line gets the signal to start the - whatever.

    And don't nobody bash me for saying "Don't nobody".
     
  10. dl324

    AAC Fanatic!

    Mar 30, 2015
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    Misspelled words and poor grammar always catch my attention. So do poorly drawn schematics.
     
  11. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    So do sentence fragments.
     
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  12. jothom

    Thread Starter New Member

    Jul 19, 2018
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    'I' was here for electrical advise not grammar, if was trying to write you some perfect literature, I would have.
    This was a very informal question but thanks for being that one forum idiot
     
  13. ericgibbs

    Moderator

    Jan 29, 2010
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    hi,
    We seemed to have drifted a little Off Topic.
    Personally, I had no problem in following the TS's detailed technical description of his query.
    E
     
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  14. jothom

    Thread Starter New Member

    Jul 19, 2018
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    Yes, I wouldn't want it any longer than 2 seconds, the machine needs to start moving as soon as possible after the brake is released (0.5 to 2 seconds)
     
  15. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    You forgot the period at the end of your sentence. OOPS! Two of us now. :)

    Just havin' a little fun this morning. @crutschow in post #7 gives you a beautiful solution. Changing the value of the resistor or the capacitor will modify the delay time. He's showing you an approximately 1.1 second delay. Since I don't know your level of electronics understanding I'll say this: A lower value resistor will shorten the time. OR a lower value capacitor. Changing either by a factor of 10 would change the timing by the same factor. Half the resistance would cut the delay time in half. Same would be true of the capacitor.

    Hope you've found a good solution to your needs.
     
    Last edited: Jul 20, 2018
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  16. danadak

    Distinguished Member

    Mar 10, 2018
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    The concern here is unpredictable logic behavior of circuits, not so much latency
    to machine operation. Eg. the need for clean fast rise logic signals to insure they
    operate logically/correctly.....

    http://www.ti.com/lit/an/scba004d/scba004d.pdf


    Regards, Dana.
     
  17. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    Just guessing here, but I think a shorter time delay, say one of around 0.5 seconds should increase the rise time transition from off to on.
     
  18. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
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    Referring to circuit #7 --

    It might be your "poor grammar", but I think you meant that a shorter delay period would *decrease* the risetime (increase the speed of the edge). If so, then you (and I) are correct.

    ak
     
  19. Tonyr1084

    Distinguished Member

    Sep 24, 2015
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    @AnalogKid Question my grammar do you? mmmMM?

    Yes. Rise quickly it will.
     
  20. crutschow

    Expert

    Mar 14, 2008
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    danadak's question is about the rise-time of the signal (how fast it changes states), not the delay.
    Can you determine if the circuit is sensitive to that?

    If so, a simple circuit can be made using a CD4106 Schmitt trigger gate IC in place of the transistor as ebeowulf17 noted, such as below:

    upload_2018-7-22_11-43-29.png
     
    Last edited: Jul 22, 2018
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