Circuit Diagram - Please can some check this for me??

Discussion in 'General Electronics Chat' started by Leckyuk, Feb 3, 2011.

  1. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    Hi All, Today I have attempted very roughly to configure a circuit diagram for a project I'm doing. I have never done a diagram before and really want it to be accurate before I post it on my project website. I'm pretty new to electronics and any help would be greatly appreciated.
     
    Last edited: Feb 3, 2011
  2. nerdegutta

    Moderator

    Dec 15, 2009
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    What do you want to achieve?
     
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  3. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    Hi There, maybe I should have put more detail. The basic structure is that a coin is inserted which then gives off a 5volt pulse at 65ma. This is not enough to trigger the relay so i used a seperate 5v circuit which is at 2 amps which is controlled by transistor, this secondary circuit at 2 amps is plenty to trigger the relay. When the relay is triggered it is essential that I do not have and current at the switching end as the closing of the gate is emulating when you press the button Number 1 on a computer keyboard.

    I have wired it all up already and works perfectly but I dont know how to put it in a diagram. Just wondered if I have done it correctly. Many Thanks for the quick reply.
     
  4. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    I know this is a really poor attempt at a diagram and I know it probably seems ridiculous to anyone who knows what they are doing so I'm sorry if it seems like a stupid request but as i've said i'm really only just getting into the refinements of simple electronics and would just appreciate a little help :)

    Thanks again and apologies for being a dumbo!!;)
     
  5. nerdegutta

    Moderator

    Dec 15, 2009
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    Maybe you want to start with getting only one powersource... In the end, will it be powered by battery or a wall socket, with a transformer?

    We all have to start somewhere...
     
  6. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    The joy of the power source is it runs off 4 core wire and directly into a PC PSU so that isn't a problem at all. Where the power sources show on the board diagram will in fact be a 4 pin connector carrying the 5v and 12v feed.

    Other than that does it look like it is correct.

    Many Thanks.
     
  7. magnet18

    Senior Member

    Dec 22, 2010
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    I don't see anything that suggests that you couldn't use the 12volt supply to power the switching portion with a simple resistor, unless your worried about interference issues

    are you building a MAME cabinet?

    [EDIT]
    also, i think you have the polarity to your transistor reversed, the emitter must be a lower voltage than the collector

    this is what i think it could look like, if its not correct im sure one of the older guys will correct me, im fairly new at this myself
     
    Last edited: Feb 3, 2011
  8. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    Thanks magnet, I have thought about the 12v single supply and agree that there is no reason why it should work! I just need 12v relays rather than 5v. Will save the hassle of a resistor then. Other than that aren't the both circuits exactly the same??
     
  9. tom66

    Senior Member

    May 9, 2009
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    You will also need a resistor on the base of the transistor. 1k to 4.7k should be fine.
     
  10. magnet18

    Senior Member

    Dec 22, 2010
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    You connected yours to the +5V where I connected it to the negative terminal of the 12V
    likewise, where you had it connected to the negative terminal of the 5V supply i connected it to the +12V

    and resistors are pretty much the simplest electrical component there is, better get used to them sometime :)

    Are you building a MAME cabinet-arcade emulator?
     
  11. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    Thanks again for that. I've built a digital jukebox. It works amazingly with my original configuration. Just don't know how to put it on paper. The resistor idea would of course be the easiest but I have 12v mini relays here already so just saves the hassle of wiring in another component! My soldering is pathetic :). The reason I'm doing this is because I did the initial jukebox just with all the components on cables, bit I'm making another and want to do this one neatly on a pcb in a project box.

    I see what you mean now, you've reversed the polarity on the secondary circuit!
     
  12. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    Hi magnet, yeah I've made a digital jukebox which I've already incorporated the previous circuit in and it works amazingly. I just didn't know how to incorporate all the symbols correctly in a diagram. I would be using resistors in the circuit but I have 12 mini relays already so one less component. I see what you mean now, you've reversed the polarity on the secondary circuit. Well spotted :)
     
  13. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    Sorry about duplicate posts lol
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    The transistor collector emitter is reverse biased.

    If you keep the relay on the emitter of the transistor you will not need a base resistor.
     
  15. Leckyuk

    Thread Starter New Member

    Jan 1, 2011
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    And Tom, why do I need a resistor at the base of the transistor? My other circuit work great without it?
     
  16. Adjuster

    Well-Known Member

    Dec 26, 2010
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    At present your circuit appears to be working with a reversed transistor, which is really bad news. It may just work with a supply as low as 5V, but probably won't last long. With a 12V supply a transistor the wrong way round would most likely fail due to base-emitter reverse breakdown. Confusingly, this circuit may be acting like a common emitter but with the emitter and collector junctions trading roles.

    If you convert it to a correct common collector circuit, with the coil still in the emitter but the supply the right way round, you
    do not need a series resistor to limit the transistor base current to a safe value. However you may find that the relay closes and opens in the wrong sense. This depends on how you really have the circuit to start with.

    If you use the more usual common-emitter arrangement (coil in the collector lead), you would normally use a base series resistor, but if
    the relay coil current is taking anything like 2A the kΩ values quoted earlier in this thread could be too big. Your circuit shows a current of 65mA from your coin acceptor, which if a true limit might be sufficient.

    Two questions therefore:

    1) What is the relay coil current (or, what is the coil resistance)?

    2) What type of transistor are you using?
     
    Last edited: Feb 3, 2011
  17. Wendy

    Moderator

    Mar 24, 2008
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    Like I said, if he keeps the relay on the emitter it will limit the current through the base. This assumes the signal on the base is great enough for the voltage follower to trip the relay though.
     
  18. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    I looked up the specs on the relay. With a 5V coil, the resistance is 180Ω. I don't see the need for a transistor.
    The relay has contacts rated at 1A max. The OP mentioned a 2 amp circuit, but I'm not sure where that is in the schematic. With a keyboard attached to the contacts, I doubt that it is in that circuit.
     
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