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Beginner's dilemma

Discussion in 'Electronic Basics' started by OldBuzzard, Sep 19, 2005.

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  1. OldBuzzard

    OldBuzzard Guest

    I just took-up electronics as a hobby. Purchased a breadboard and a fe
    jumper wires(?). And am waiting to light-up my first LED. I have
    resistor of 657 Ohms( or K Ohms;blue, green, brown and gold bands). M
    question is, can I strip the ends of a mobile phone charger and connect i
    to my breadboard as a power supply ? It does say on the charger that th
    output is about 5V / 500mA.

    Any help will be appreciated.



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  2. John Fields

    John Fields Guest

    The resistance of the resistor is 650 ohms, and the tolerance on
    that value is +/- 5%.

    The first color band indicates that the first significant figure of
    the value of resistance is blue (6), the second is green (5), and
    the third indicates that the decimal multiplier ( the number of
    zeroes after the second significant figure) is brown (1). The
    fourth band, gold, indicates that the tolerance is +/- 5%. Ergo,
    650 ohms, +/-5%.

    It's difficult to say whether your charger will make a good power
    supply since it's designed to charge your cellphone batteries and
    may supply more than 5V if it's not loaded properly. It also may
    produce what's called "ripple" which may not be acceptable for a
    breadboard supply. What kind of test equipment do you have
  3. That will work. However i would recomend a powersupply with higer voltage if
    you are interested other things. I guess its ok for simple circuits and
    digital stuff. Working with audio circuits would often require a more
    powerful PSU.

    Just rember that leds dont like to much current. 20 -30 mA is often the max
    value. It will work fine with the resistor you have. 5 V / 650Ohms = 7.6mA.
    You could even wire 65 leds in this fashion and the PSU would still do. ;)
    Maybe you could wire a similar resitor in paralell to make it brighter. Then
    the current would be 15.2mA. Now you only could wire 32 leds.

    Just remember that leds are polarised devices. If you can feel the flat edge
    on one of the sides of the diode. That pin will got to the negative (ground)
    side of the PSU. Hope you have a multimeter.

    Have fun.

    Anders N. Vinje
  4. 650 ohms isn't a standard value, according to my references - the OP
    should check the colour code again. The nearest standard values to
    650 are 620 (blue red brown) or 680 (blue grey brown)
  5. John Fields

    John Fields Guest

  6. Jim Gregory

    Jim Gregory Guest

    If you are not yet equipped, buy a small cheap handheld multimeter, analogue
    or digital, and makes sure it
    has a diode test and a beeper continuity range. They are very cheap
    nowadays. Read the accompanying booklet!!
    RESISTOR values (unwired, out of circuit) are easy to prove by reading the
    display! No such commonplace thing as a 650 Ohm.
    Some efficient LEDs are happy running at down to one mA.
    Caution! You said your power supply is a charger so it might give a much
    higher voltage (maybe +33%) than it quoted if just driving an LED. But 560r
    is a safe dropper at 7-8V DC.
  7. Chris

    Chris Guest

    Or possibly 750 ohms, also a standard value. It might be as easy to
    mistake violet for blue as it would be to mistake red or especially
    grey for green.

  8. JeffM

    JeffM Guest

    I have a resistor of 657 Ohms
    The same thing struck me so I checked my chart

    657 is a standard value--for 0.5% or better
    Of course, it would take more bands.
    Not sure where the OP got that number.

    I wondering if Chris Foley didn't call it right
    when he alluded to color perception problems.
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