Designing a simple alarm signalling circuit

Discussion in 'The Projects Forum' started by nestbulala, Oct 9, 2016.

  1. nestbulala

    Thread Starter Member

    Dec 12, 2015
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    Dear Experts,
    I am designing a simple alarm signalling circuit for our legacy alarm board. I am very much concern about the scr and the latch circuit if it does what I am expecting. Can anybody advise on the attached circuit?
     
  2. Alec_t

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    Sep 17, 2013
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    Exactly what are you expecting?
    Can you post a clearer image?
     
  3. R!f@@

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    Apr 2, 2009
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    That circuit is way wrong for so many reasons.
     
  4. R!f@@

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    1. 50V Relay ????
    2. What does 555 do ????
    3. What does opto do????

    Who designed that monstrosity ???
     
  5. nestbulala

    Thread Starter Member

    Dec 12, 2015
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    R!f@@, the 50 volt relay should be 48 volts that will triggered when there is an alarm, the 555 will flash the opto-isolator at 1 hz and clamp the lamp to the negative side of the power rail. Sorry for the design, I did it the simplest way I can and I borrowed from the internet. That is why I came here to you guys. Alec_t, I don't have a clearer picture but I can try to change it to png file.
     
    Last edited: Oct 9, 2016
  6. nestbulala

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    Dec 12, 2015
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    Alec_t, this is the clearer picture. Alarm Circuit Module Schematic Diagram5.png
     
  7. R!f@@

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    It won't flash. Not the way the bulb is connected
    And the opto cannot drive a 5W bulb

    Lamp test and Alarm switches are the same
     
  8. nestbulala

    Thread Starter Member

    Dec 12, 2015
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    Ok then R!f@@, the opto-isolator will drive a transistor to drive the bulb. It should flash from the 555 right? How should I connect the bulb? Alec_t, I am expecting that when when the alarm is triggered and you acknowledge, the scr should remain on until the power is removed.
    R!f@@, I modified the lamp connection I hope this will be ok.
     
    Last edited: Oct 9, 2016
  9. R!f@@

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    U need atleast 100mA with 100V rating to drive a 60V,5W bulb
     
  10. R!f@@

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    check.png

    Disconnect the wire in the circle
    And add a transistor as said before
     
  11. Alec_t

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    Sep 17, 2013
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    Ah, much clearer. My old eyes couldn't decipher the original :).
     
  12. Alec_t

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    When the Alarm signal goes there is no supply for the SCR (or the lamps), so the SCR will switch off.
     
  13. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    Also the voltage regulation circuit D1,Q1 and R1 will not work.
    There is no voltage going to the circuit unless one of the buttons is pressed.
    As soon as the buttons are released, no voltage is present at the circuit.
    Should the alarm start when the alarm button is pressed?

    Bertus
     
  14. nestbulala

    Thread Starter Member

    Dec 12, 2015
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  15. nestbulala

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    Dec 12, 2015
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    Bertus, the alarm switch is latching when there is active alarm, it will remain on until it is cleared. D1, Q1 and R1 will work only when there is alarm.
     
  16. bertus

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    Apr 5, 2008
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    Hello,

    The schematic does not show the latching.
    Is it a mechanical latching?

    Bertsu
     
  17. Alec_t

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    Sep 17, 2013
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    You are applying the same voltage to the anode, cathode and gate of the SCR, so it won't switch on.
    When the Alarm signal is present both lamps will be on, regardless of the 555 operation.
    If the Alarm signal is a latched one why do you need the SCR?
     
  18. nestbulala

    Thread Starter Member

    Dec 12, 2015
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    Modified lamp connection because it will remain on if alarm is active. Alarm Circuit Module Schematic Diagram7.png
     
  19. Alec_t

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    Sep 17, 2013
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    The Alarm and Acknowledge signals are now commoned.
    The lamps and SCR anode have no supply unless the Lamp Test switch is closed.
    Applying 50V via R5,Q2,R4 to the 555 output pin will probably fry the 555.
     
  20. nestbulala

    Thread Starter Member

    Dec 12, 2015
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    Alec_t, I expect that when the alarm is active, the 555 will flash, when you acknowledge it should remain on by the SCR. About the Q2, probably I need an opto-isolator which was from the previous design.
     
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