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Using USB or wall charger to power breadboard

Discussion in 'General Electronics Discussion' started by lefam, Nov 30, 2010.

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  1. lefam

    lefam

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    Nov 18, 2010
    Hi guys!

    Is there any problem to use USB power directly from a PC (like a laptop) to power a breadboard?

    What about wall chargers? Can I use them to power breadboards?

    Thanks in advance!
     
  2. LTX71CM

    LTX71CM

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    May 23, 2010
    Not if you don't screw something up. Problem is a slip is bound to happen and you might short the USB power or similar. It's easier and cheaper to replace a wall wart than a PC or laptop.

    Yep. Just make sure the voltage and current specs meet your needs and that it's DC (for DC circuits). Keep in mind that cheap unregulated wall adapters can be rated for 11VDC (applies to all voltages, 11 is just an example) but output upwards of 15 volts with little to no load.
     
  3. lefam

    lefam

    43
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    Nov 18, 2010
    Hi. Thanks for answering.

    I am new to electronics.

    How could I short the USB when making connections with the breadboard?

    What does VDC means? What is an unregulated wall adapter?
     
  4. davenn

    davenn Moderator

    13,676
    1,892
    Sep 5, 2009

    you mite accidently put a short circuit across the +5V and the ground connection from the USB cable
    where it connects to the breadboard the breadboard or some where else in the circuit.

    This at least could damage and make the USB port unuseable
    At worst, seriously damage the computer.

    VDC = Volts Direct Current ........ VAC = Volts Alternating Current


    cheers
    Dave

    DC power supplies come in 2 main flavours

    Unregulated ... this means that the AC from the transformer goes to rectifier diodes and then to the
    output with a smoothing capacitor between the +VDC and 0V the voltage has NOT been stabilised
    and as LTX71CM said a power supply, say 12VDC may have a no-load output of up to around 16V

    Regulated .... after the rectifier and smoothing capacitor there will be a regulator Intergrated Circuit
    say a LM7812 this will produce a smooth stable12VDC output even when the input voltage varies a bit.

    google LM7812 and find out how it works :)
     
    Last edited: Dec 1, 2010
  5. lefam

    lefam

    43
    0
    Nov 18, 2010
    Thanks for your answers.

    So, in a USB a short circuit happens when I directly touch the +5V and GND endpoints (pins)?
    In a wall wart a short happens touching directly the (-) e (+) endpoints?

    Are these the unique ways of generating a short?

    How do I know if a wall wart is regulated?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    A short is a direct connection between any 2 points in a circuit. Often it is used to describe something unexpected, or in error, but it can be used to describe an expected situation (as in "You expect to see a short circuit between the ends of a power cable", or "if the fuse doesn't look like a short circuit, it's blown").

    A short (which is an abbreviation of "short circuit") is not necessarily going to damage anything, but it represents a low (often near zero) resstance, so where there is a potential difference between the points shorted, and where the source of that potential difference can supply significant current, bad things can happen.

    A power supply is an example of a device which supplies a voltage (the potential difference) and which can supply possibly significant amounts of power. Some power supplies cannot tolerate a short and the excessive current drawn will damage them. When the power supply is your expensive (well relative to a wall wart) then you don't want to risk it.

    A wall wart may not be designed to handle overload conditions either, and it may be damaged by excessive current draw (a short being the most extreme example). But at least it's cheap.

    The real solution is to have a voltage regulated and current limited (perhaps foldback current limited) power supply. These are typically built to handle short term overloads.

    The power supply surviving is a good thing, but the short can damage components on your circuit under development on a breadboard -- but that's the risk you take. With leaded components, it is very easy to accidentally short (say) one resistor lead to another in the rats nest that breadboards can become.

    How do you know if a wall wart is regulated? Easy! Measure the voltage on it without any other load. If it is very close (say under half a volt) to the voltage stamped on it, then you can be pretty sure it's regulated.

    If the wall wart is very light, then chances are that it is a switchmode regulator and it will be regulated (another dead give-away is an extended input voltage range -- say 90 to 250 volts).

    Heavy wall warts contain a mains transformer (these are becoming rarer and rarer) and will often have a voltage reading under no-load conditions of between 20 and 50 percent higher than the rated voltage (so a 12 volt wall wart could measure between 14.5 and 18 volts -- probably closer to the latter).
     
  7. lefam

    lefam

    43
    0
    Nov 18, 2010
    I am considering powering my breadboard with a wall wart.

    Is it safe to just strip the wall wart connecting wires and connect to the breadboard? Is this the correct procedure.

    Thanks for all your replies. I learned a lot!
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Yep, that is fine. As long as you do it with the power off :)

    You might find that the wires are too thin to easily push into the breadboard.
     
  9. lefam

    lefam

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    Nov 18, 2010
    I have a 5V regulated wall wart. How can I prepare it to use in my breadboard? Its wires are too thin.
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The easiest way is to get some solid core wire that is suited to your breadboard and solder a short length to the end of the wires. Then use heatshrink, or tape to provide some protection (and mechanical stability) to the joints.

    I would make one lead longer than the other so that if the cable is pulled out, the ends do not naturally come together. You can do the same for the joints too so that if the insulation gets removed, the joints are not next to each other.

    so something like this:

    -----------------------joint=================----
    --------joint==============----
     
    Last edited: Dec 1, 2010
  11. lefam

    lefam

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    0
    Nov 18, 2010
    thank you. I will try.
     
  12. barathbushan

    barathbushan

    223
    0
    Sep 26, 2009
    Wall mart's are good for beginners in electronics , but nothing can beat your self made power supply !!!

    But if you dont want to build your supply , you can try this , it was really helpful when i started out .
    It also has got "SHORT CIRCUIT PROTECTION"

    [​IMG][​IMG][​IMG]
     
    Last edited: Dec 8, 2010
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