Relay Pulse timing - milliseconds rather than seconds

Discussion in 'General Electronics Chat' started by kellery, Feb 20, 2016.

  1. kellery

    Thread Starter New Member

    Feb 20, 2016
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    1
    Hi all,

    I apologise if this is the wrong section of the forum or the wrong forum to actually post a question to. I have searched the forums here and haven't been able to find something similar around my problem and sorry for the long story below.

    I have an alarm system which has a relay board in it to operate external outputs (12v). The alarm system has settings per relay output to adjust the pulse time from 1 second to 60 seconds. I have successfully connected two outputs to two garage doors (tilt doors), which enables me to open them with the alarm system (pulse time is set to 5 seconds which these two doors don't have an issue with). I have tried connecting a third garage door (roller door - different motor to the other two), but am having an issue.

    With the Pulse time set to 1 second, and activating the relay output, the door will open about 15cm's and then stop. After investigating further, it appears that the garage door motor for this roller door is very sensitive - if I connect the wires together very quickly and remove (so not connected to the alarm at the moment, just testing the motor), the door opens all the way fine, and the reverse when closing. If i connect the wires together and hold for 1 second (replicating the pulse time of the alarm), the door will only open about 15cm's (same issue as the relay output on the alarm.) So it seems that a 1 second pulse time is too long for the relay.

    I have been searching but can't find a relay that has a adjustable pulse time from 1 second to perhaps milliseconds as i believe that this is what is needed (i can have the alarm relay drive another relay that has a millisecond pulse time and run the door of this).

    Is there any way around this issue or do you guys know of where I can get a millisecond pulse time relay or adjust a standard relay's pulse time?

    Thanks in advance, and I apologise, i'm not very good when it comes to electronics.

    Regards

    Kristopher
     
  2. Ramussons

    Active Member

    May 3, 2013
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  3. crutschow

    Expert

    Mar 14, 2008
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    Since you want an output pulse shorter than the input pulse then, for a 555 circuit, you need to differential the trigger pulse as shown here under the paragraph "Trigger pulses".
    Otherwise the output pulse will be longer than your input trigger.
     
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  4. kellery

    Thread Starter New Member

    Feb 20, 2016
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    Thanks guys , I appreciate your help. I'll have a look at both links.

    Regards,

    Kristopher
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  6. crutschow

    Expert

    Mar 14, 2008
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  7. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,797
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    A simple resistor/capacitor combo may be all that you need. Is the door controller expecting a negative-going or a positive-going control pulse? What voltage?
     
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  8. dannyf

    Well-Known Member

    Sep 13, 2015
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    Couple the two systems through a capacitor. Adjust the capacitance to control the pulse width.
     
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  9. kellery

    Thread Starter New Member

    Feb 20, 2016
    6
    1
    Hi all, thanks for your replies.

    I've spoken to a friend who installed my alarm system and he has advised that for the motor "it’s a Dry contact. There is no voltage."

    He advised that "it’s not neg or pos, its just two wires touching. Just unfortunately that motor wants it to be super fast".

    Would a monostable 555 timer still be suitable with a differentiator and or adjusting the capacitor C1, or couple the two systems through a capacitor.

    Again sorry, electronics is not something I'm totally familiar with.

    Thanks again,

    Kristopher
     
  10. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    if its joining two wires together, the relay contacts will do that for you on the 555 timer pcb.
     
  11. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    Given the general nature of motor controls and buttons pushed by humans, this does not make sense. The solutions are fine, but the problem is a problem. Why is the one motor controller so picky about unreasonably short actuating pulse times? I think the real solution is there.

    Separate from that, relays are not fast responding devices, which probaby is the reason the alarm system does not adjust below 1 sec. So it sounds like the plan is that the alarm system fires its relay, that triggers a monostable, that fires a second relay for a much shorter time, and that relay's contacts operate the motor controller. Yes/No?

    ak
     
  12. kellery

    Thread Starter New Member

    Feb 20, 2016
    6
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    Hi all,

    Again, appreciate you replies.

    Yeah i think your suggestion ak is the way to go.
     
  13. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    I'm not suggesting anything. I asked if I had summarized correctly your plan.

    ak
     
  14. kellery

    Thread Starter New Member

    Feb 20, 2016
    6
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    Yes, sorry ak, you have summarised the plan correctly.

    I didn't read your post correctly this morning
     
  15. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    My garage door motor heads have a schematic on the inside of the cover. It sure would be nice to know exactly what your control input is, and how "dry" the dry contacts have to be. For example, the output of an optocoupler is fully isolated, but unidirectional. Some can sink over 1 A, and all respond much faster than an electromechanical relay. Make/model of the opener, manufacturer's tech support...?

    ak
     
  16. kellery

    Thread Starter New Member

    Feb 20, 2016
    6
    1
    Hi All,

    Thanks for all your advice. I purchased the same monostable 555 timer as suggested by DodgyDave from a local source within Australia, and have fitted to the alarm system after the alarm system's relay and before the connection to the motor and it has solved my issues (the door now opens and closes fully).

    Without all your valuable feedback and knowledge, I would not have known where to start as my electronics knowledge is very limited.

    Appreciate all your help.

    Regards,

    Kristopher
     
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