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6 Buzzer Project

Discussion in 'General Electronics Discussion' started by droidH, Jan 16, 2013.

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  1. droidH

    droidH

    6
    0
    Jan 16, 2013
    Essential parts (ALL IN DC):
    x6 - buttons
    x6 - light bulbs
    x6 - buzzers

    About the project:
    It should work the same in quiz bowls where they press a button and a light comes up with a buzzer. The buzzers will be grouped into 2, for team A and team B. Whenever any of the button is pressed the others should be turned off, so it's like first come first served. I have already the connection for the buttons, light bulbs, and buzzers but I can't solve the problem on how to turn off the others if one button is pressed.

    MCU are not required here. First of my thought is using relays. I just can't get the idea where to place them to make the project work. Anyone got thoughts? Thanks.
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Have you looked here?
     
  3. droidH

    droidH

    6
    0
    Jan 16, 2013
    Already tried googling it but I can't find the one i'm looking for or it just don't pass the required system. And mostly google is showing systems that is controlled by MCU which I can do it easily but due to the restrictions it's impossible.

    That's why I came upon this forum thinking someone might suggest an idea.
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    You would have saved time if you had said so before.

    That Google search found a page http://www.satsleuth.com/schematics.htm which has links to several relevant designs:
    http://www.techlib.com/electronics/games.html
    http://www.desmith.net/NMdS/Electronics/Jeopardy.html
    http://www.zen22142.zen.co.uk/Circuits/Misc/quiz.htm
    http://www.ee.washington.edu/circuit_archive/circuits/F_ASCII_Schem.html#ASCIISCHEM_002 (same idea as the first one)
     
  5. KMoffett

    KMoffett

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    Jan 21, 2009
  6. droidH

    droidH

    6
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    Jan 16, 2013
    Thanks for the links. After seeing them all I tried making the system using a simulator. The system had about 15 relays in it and adding more would cause problems.

    In extending my searches i'm beginning to think that what i'm trying to make is a lock-out buzzer system.

    Thanks for the link. I'm just having a hard time converting the examples to my own specification
     
  7. KMoffett

    KMoffett

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    Jan 21, 2009
    This is the simplest one I've built. Minimum components. Expandable to any number of stations. You don't really need a separate buzzer for each contestant, the lights show who "buzzed in".

    Ken
     

    Attached Files:

  8. droidH

    droidH

    6
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    Jan 16, 2013
    Thank you for the example. I'll study this first and get back to you.

    With a possibility that those thyristors and zenere doide are not sold locally, can I replace them any kind of thyristors and zenere doide? The source would be a 24v dc
     
  9. KMoffett

    KMoffett

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    73
    Jan 21, 2009
    This is a good reason to fill in your location in your profile. Then we can suggest resources. Other SCRs would work. Not a lot of options for a Zener.
    Why 24V? Is that your only option for power source?

    Ken
     
  10. droidH

    droidH

    6
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    Jan 16, 2013
    24V is just the max power source that I can use if I would use a 24V buzzer and light.

    By the way this is the circuit i was working on. It doesn't work. When the simulation runs, all the relays goes off for no reason and it never stops.

    Group A on the left and Group B on the right. If any of the buzzer in group A is pushed, the remaining buzzers in Group A are disabled and also Group B buzzers are disabled too and vice versa.

    I haven't thoroughly studied the one you gave because of other school stuff.
     

    Attached Files:

  11. droidH

    droidH

    6
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    Jan 16, 2013
    Tried to rewire it again but still doesn't work. I think I know I'm doing something wrong but I just don't know what. Using a relay is part of the requirements for the system so I can't remove the relays.
     

    Attached Files:

  12. KMoffett

    KMoffett

    719
    73
    Jan 21, 2009
    24VDC! Relays required! Is this a class homework project?

    Ken
     
  13. Raven Luni

    Raven Luni

    798
    8
    Oct 15, 2011
    Well if you have to use relays that means you can use lower voltage and discrete logic and all the relays do is switch the bulbs.
     
  14. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    OK. You said you thought this could be done with relays. Here's one way to do it with relays, lots of diodes, and a few small components. No active semiconductors.

    [​IMG]

    I've posted this design to show that it's possible, but it may not be practical, depending on your requirements, because of the delay of several milliseconds between the relay coil being energised and the relay contacts changing over fully. This delay is inherent in the relays and will cause problems if two or more buttons are pressed within a few milliseconds of each other - possibly two or more buttons will be latched; possibly none will be.

    I've chosen a nice compact and quick relay, the TE Connectivity V23079A1005B301 (see http://www.digikey.com/product-search/en?x=0&y=0&lang=en&site=us&KeyWords=V23079A1005B301). It's also very cheap. It has a specified pull-in delay of about 4 milliseconds and a coil current of about 5.8 mA. This is a factor in the choice of the value for CC, as described below. The alternative relay mentioned on the schematic has a coil current of about 9 mA and is also suitable. Do not substitute a relay with a higher coil current requirement without changing CC.

    Here's a circuit description.

    Initially all relays are de-energised. The +24V supply flows through the top normally closed contact of K1, out to K2, through K2, and so on, and eventually reaches RC, which charges CC up to +24V fairly quickly (T = 10 ms). The voltage on CC is supplied to the pushbuttons.

    The six sections are almost identical so I will only describe the first one in detail.

    When pushbutton SW1 is pressed, current flows from CC, through SW1, through DP and into the relay coil. The relay coil draws 9 mA or less; at this current, a 10 uF capacitor will keep the coil voltage above the guaranteed pull-in voltage of 18V for about 7 ms, long enough for the relay to pull in fully.

    As soon as the relay pulls in fully, its bottom contact latches it on (via DL, the latching diode) and illuminates the appropriate lamp, and its top contact switches from +24V to 0V. This new voltage propagates through the other relays as before, and discharges CC rapidly through DD and RD, preventing any other relays from being activated if another contestant pushes his button after the first button-press has been accepted.

    When any relay is closed, DB feeds 24V into the buzzer. Pressing SW7 removes the supply voltage and forces the relays to drop out. DK protects other circuitry against back EMF from the relay coil when it de-energises and is probably not needed in this design, but it's small and cheap so better safe than sorry. RC and RD will dissipate more than their rated power for short periods of time when the circuit starts up (RC) and when a button is accepted (RD). Use good quality metal film resistors, or wirewound resistors, for these positions.

    It might be possible to avoid CC and associated components by connecting the normally closed contacts of all relays in series in between the 24V supply and the pushbutton rail, so that the pushbutton supply disappears immediately when any relay activates and its normally closed contact opens. This does not necessarily guarantee that the first activated relay will pull in fully, and could lead to this relay becoming a buzzer in itself, as it rapidly alternates between states without the bottom NO contact ever making contact and latching the relay through DL. The manufacturer might be able to advise whether that change would be reliable; it would certainly improve the circuit's ability to deal with closely timed presses on different buttons.

    Edit: I haven't simulated or prototyped this design!
     

    Attached Files:

    Last edited: Jan 20, 2013
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