switches relays asking for help

Discussion in 'General Electronics Chat' started by cellage, Oct 18, 2010.

  1. cellage

    Thread Starter New Member

    Oct 18, 2010
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    Help am new to the electronics world and i need to understand switches , how to control a switch though a pic microcontroller output , what kind of switch , relay ? is required
    i need that circuity to control a light bulb and a (motor and thats another issue )
    am kind of lost here
     
  2. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    You need to specify the voltages and currents (AC?, DC?) that the bulb and the motor require.

    Ken
     
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  3. SgtWookie

    Expert

    Jul 17, 2007
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    Microcontrollers aka MCU's and uC's have very limited current sink/source capability; usually +/-20mA maximum per I/O pin. You'll need to use a driver circuit to control the current in a relay's coil.

    Here's one way to use a logic-level N-channel power MOSFET:

    [​IMG]

    You can use basically the same circuit with an NPN transistor instead of a MOSFET; emitter gets connected to ground, base to the resistors, collector sinks current from the relay's coil.
     
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  4. cellage

    Thread Starter New Member

    Oct 18, 2010
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    Thanks very much for the instant replay :)
    i have this circuit but i couldn't simulate it via orcad capture it cant identify the relay ! so i dont know weather its working or not
    i intend to put a light bulb 60W and fix the current and voltage according to that. Its very simple but still not sure

    [​IMG]
     
  5. radiohead

    Active Member

    May 28, 2009
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    The relay is simply a switch that can handle a larger current load. The relay is actuated by a controlling circuit. If you look at your circuit above, you have no power source to make your light bulb light. Try putting a voltage source in series with your lamp, then use the relay to switch it on and off.
     
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  6. cellage

    Thread Starter New Member

    Oct 18, 2010
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    thanks that was helpful all pf you are so kind
     
  7. cellage

    Thread Starter New Member

    Oct 18, 2010
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    what kind Of relay do you advice me ? give me some specific options if you please there is a lot of relays
     
  8. radiohead

    Active Member

    May 28, 2009
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    The type of relay depends upon your load current. A standard 12VDC/30A automotive relay should work well.
     
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  9. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    The bulb image the OP posted (#4) looks like a 60W 120VAC (or 240VAC) bulb. Not a good idea to use a 12VDC contact rated relay on high voltage AC. But then the OP hasn't really spec'd that.

    Ken
     
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  10. cellage

    Thread Starter New Member

    Oct 18, 2010
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    do you suggest that i change the light type ? or if not how can i provide a suitable voltage to the bulb ?
    does the relay provide a voltage that make me discard the voltage source i put parallel to the resister named light ??
     
  11. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    I think the voltage/current/wattage of the bulb or motor is entirely up to you. You have to tell us what you want to use. Then we can help with the details. Or, is this just a paper design, with no real components?

    Ken
     
  12. cellage

    Thread Starter New Member

    Oct 18, 2010
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    thanks all for responding
    its a real design i simply thought about this light bulb cause its available
    now am confused the relay will have a voltage of 12 volt with current 30-60A so can this voltage turn the light on ? or i need another voltage source parallel to the light ?
    by the way this circuit is supposed to be controlled through a PIC microcontroller
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Do you really need to turn on a 60W light bulb that is powered by the mains?

    If so, you will need to find a suitable relay. Automotive relays are not designed for that kind of service.

    I really prefer that new people stick with low-voltage projects for awhile. Working with mains power can be quite hazardous.

    Why don't you consider using automotive lamps instead? They are also readily available, and operate from 12v-14v, which is quite safe to work with.
     
  14. cellage

    Thread Starter New Member

    Oct 18, 2010
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    well thanks for alerting me i will consider that and use an automotive lamp and look for a low voltage as you advised :)
    so after changing the light type I should choose the relay depending on the new voltage rate
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    Yes.

    You can then use automotive-type relays, as they are made for the same voltage.

    Your 5v supply for your PIC will need to share a common ground with the 12v supply, or else you will need to use an optocoupler.
     
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  16. 8_INCH_FLOPPY

    New Member

    Oct 22, 2010
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    0
    You could always just attach a solenoid to your standard home-wall-switch, and plug your motor/light into the corresponding wall-outlet. It's kinda jerry-rigged, but it might be cheaper than finding a proper relay, and, assuming you have an extra light-switch-controlled outlet, you don't have to risk coming into contact with mains.
     
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