555 Debounce on the + Side?

Discussion in 'The Projects Forum' started by Dan-O, Aug 1, 2009.

  1. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Hello folks, first time posting so go easy on me.
    I'm an amateur that knows just enough to get into trouble.

    I'm designing a vehicle pushbutton start using a 4013 flip flop circuit for the vehicle power and a 555 with a 1 second delay for the start function.

    In planning ahead, I think I might need a debounce for the input to the 4013 so I don't flop when I want to flip.
    (Sorry about the bad joke)
    The input to the 4013 is a +12V input controlled by a relay activated by a momentary switch.

    Could someone point me to a debounce that's on the + side of the input instead of the usual - side that I find?
    Thanks for the help.
    Dan
     
  2. CDRIVE

    Senior Member

    Jul 1, 2008
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    Have you considered just using simple a RC input to the FF?
     
  3. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Do you have an idea on what values I should use for the components?
    Most of the RC circuits I find are negative trigger. Is it a matter of reversing the cap in the circuit?
    Please forgive my ignorance of stupid questions.
     
    Last edited: Aug 2, 2009
  4. CDRIVE

    Senior Member

    Jul 1, 2008
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    I would think a 1K resistor on the switched side of the push button and a 0.01uF to 0.1uF to gnd should do.
     
  5. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Thank you I appreciate the help.
     
  6. CDRIVE

    Senior Member

    Jul 1, 2008
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    I just re-read your first post and I made a boo boo! If the FF is being triggered by the contacts of a relay then the RC filter should be connected to the switched side of the relay contacts, not the switch . Sorry....! :eek:
     
  7. CDRIVE

    Senior Member

    Jul 1, 2008
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    Please see attachment. Is this how you're wired?
     
    Last edited: Aug 2, 2009
  8. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Yes. I knew you meant to connect the RC components on the relay side.
    I am using the 4013 circuit here--> Click Link but with a relay instead of the switch.
    So if I'm reading it and your suggestions correctly, it already has the 'debounce' built in?
    Thanks again for the help.
     
    Last edited: Aug 2, 2009
  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    Yeah, that circuit already has a 100K and a 1uF cap in there. That should give ample immunity from contact bounce. ;)
     
  10. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Sweet.
    Thanks again for the information and the reassurance.
    Dan
     
  11. CDRIVE

    Senior Member

    Jul 1, 2008
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    Dan-O I forgot something else too!!!

    To say..
    WELCOME TO THE FORUM!!:D
     
  12. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Well, I finally had a few minutes to tinker.
    I'm having some issues.:(
    The 4013 is really sensitive to noise/contact bouncing.
    I think I might need a more aggressive way to debounce the + switch input to the 4013.
    I misspoke in an earlier post, I do have a switch input not a relay input to the 4013.
    I am using the 4013 circuit here--> Click Link

    The way my circuit works is by holding a shared pushbutton + input (both the 555 and 4013 share the same + input)
    A relay engages and the engine cranks through the 555 after 1 second. That end works perfectly. But, as soon as I release the switch, the 4013 shuts off the vehicle power relay.
    Suggestions?

    Also, should I have a diode or a resistor from 11 to my transistor? I'm using a 3904 with the base connected to pin 11 of the 4013.

    Thanks for the input.
    Dan
     
  13. CDRIVE

    Senior Member

    Jul 1, 2008
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    Dan, could you please post your complete schematic? It will make diagnosis much easier. As they say "A picture is worth a thous..... "
     
  14. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    I found a schematic of what I'm doing with the 3014 and modified it with the transistor I have to control the relay coil. Not pictured is the usual clamping diode across the coil for spikes.
    I appreciate the help.
    Dan
     
    Last edited: Aug 23, 2009
  15. CDRIVE

    Senior Member

    Jul 1, 2008
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    There should be a 1K resistor between the base of the NPN and the chip.
     
  16. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Thanks, I added it.
    Do you think that was angering the 3014 and causing my issue?
    I added the 555 and updated my schematic.
     
    Last edited: Aug 23, 2009
  17. CDRIVE

    Senior Member

    Jul 1, 2008
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    You have a few things wrong here.
    (1) The base resistor should be ~ 1.0K not 100K. 100K will not provide enough base current.
    (2) The 555's vcc (pin8) should be connected to the 12V supply.
    (3) You may also need a driver transistor for the 555 relay coil. What's the current draw for that relay.

    There may be more but I have to get some sleep.
     
  18. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Current draw is low, it's not a typical Bosch relay. I have to look it up, but I believe the coil resistance is up there, like 720 ohms or so.
    I made some revisions to my schematic.
    Thanks for the help.
    Dan
     
  19. CDRIVE

    Senior Member

    Jul 1, 2008
    2,223
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    Try this configuration.;)

    EDIT: For bystanders reading this thread, please read subsequent posts.
     
    Last edited: Aug 24, 2009
  20. Dan-O

    Thread Starter Active Member

    Jul 26, 2009
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    Hmm, there's a few things I don't understand: What are the TP notations in the schematic?

    Actually, I don't have an issue with the 555 doing it's job; the 1 second starter delay is working great.
    The issue I have is with the 4013 not changing state.
     
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