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Project using LEDs and Switches

Discussion in 'Electronic Basics' started by Ken, Nov 26, 2003.

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  1. Ken

    Ken Guest

    Hey, I'm pretty new to electronics and I decided to start by building
    a simple circuit using some LEDs, some switches, and a DC adapter. Not
    very fancy, there are 5 groups of LEDs wired in parallel, each with
    its own unique switch, but they all share the DC adapter for power
    (only one set of lights needs to be on at one time, so I'm not worried
    about regulating the amount of current). Using ohm's law, I
    calculated the correct number of LEDs to use in each group to divide
    the current down to an appropriate level. Now for my problem:

    When i flip any of the switches, every group comes on. I realize
    that this is in some way because they all share a common power supply,
    but beyond that I'm stuck. I read somewhere that a diode might solve
    this. I'm not entirely sure how a diode would help though. If
    electricity flows from negative to positive, why do I need to
    introduce a new structure for doing that? Or am I not getting the idea
    of diodes? I don't even though if that's the right way to go. I read
    somewhere else about logic gates, which also seems like a possible
    solution. However before I continue, I'd like to try and understand
    exactly what's going on. Any help anyone could give would be greatly
    appreciated.
     
  2. John Fields

    John Fields Guest

    ---
    How many LEd's are there in each set?
    What current are the individual LED's rated for?
    What color are the LEDs/what is their rated forward voltage?
    Are you mixing colors in a set?
    What voltage and current is your DC adapted for?
     
  3. RD

    RD Guest

    ? give us some idea of the circuit, this should work.

    Adapter+_________________________
    | | |
    \ \ \
    Switches
    | | |
    LED LED LED or more than one
    | | |
    R R R
    | | |
    Adapter- _|____________|____________|

    It's easy to blow an LED with over current so you should use a limiting
    resister
    RD
     
  4. Ken

    Ken Guest

    How many LEd's are there in each set?
    16
    Green, Yellow, and Red (I believe they range from 1.8 - 2.2 volts)
    Yeah, two of the sets have a mix of Green, Yellow, and Red
    300 mA at 3 volts
     
  5. Ken

    Ken Guest

    ? give us some idea of the circuit, this should work.

    Yeah, minus the resistor that's what i have, except the switches on
    the other side, i guess what you would call the "hot" side??. (DC-)
    goes to all the switches and all the LEDs go to (DC+). Could this be
    my problem?
     
  6. John Fields

    John Fields Guest

    Since your supply is 3V, you won't be able to run any LEDs in series so
    you'll need to use a separate resistor for each LED. You can determine
    the value of the resistor by subtracting the LED's forward voltage from
    the supply voltage and then dividing the difference by the LED current.
    For example, with a 3 volt supply and an LED Vf of 1.2V, R =
    (3V-1.2V)/0.02A = 90 ohms. 91 ohms is a standard 5% value, and to
    determine the wattage the resistor needs to dissipate you take the
    difference between the supply voltage and the LED Vf and multiply that
    by the LED current: P = (3V-1.2V)*0.02A = 0.036 watts, so you could use
    a 1/4 watter.


    Arrange your switching like this and you should be fine:

    (View with a fixed pitch font like Courier)

    GND>-----------------------+
    |
    3V>--+--> | |
    | | |
    | O SET 1 |
    | | |
    | +--[R]---[LED>]--+
    | | |
    | +--[R]---[LED>]--+
    | . .
    | . .
    | . .
    | +--[R]---[LED>]--+
    | |
    | |
    +--> | |
    | | |
    | O SET2 |
    | | |
    | +--[R]---[LED>]--+
    | | |
    | +--[R]---[LED>]--+
    | . .
    | . .
    | . .
    | +--[R]---[LED>]--+
    | |
    . .
    . .
    . .
    TO REMAINING SETS
     
  7. What's wrong with Google? Has it gone stark-raving mad? I did a
    search for Wire OR, and came up with 17,500,000 hits. So then I put
    it in quotes, and _still_ got 17,500,000 hits! So I changed it to
    "wire OR circuit" and I got 19,500,000 hits!!!

    Anyway, when Google regains its sanity, do a search for Wire OR
    circuit. :-/


    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  8. You should use Courier or other fixed space font so your drawing
    doesn't come out all whacko.

    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  9. I'm trying to determine exactly how your circuit is connected. You have a 3V
    dc source, and the anode (long lead) of a bunch of LEDs are connected
    directly to it. Then, for each LED, you have a separate switch. One side of
    the switch connects to the short side of the LED, and the other side of the
    switch connects to 0V (the DC- or ground).

    When you turn on one of the switches, all the LEDs turn on.

    Is that right?

    Regards,
    Bob Monsen
     
  10. Ken

    Ken Guest

    Since your supply is 3V, you won't be able to run any LEDs in series so
    The side that says "3V" is positive and "GND" is negative, right? I'm
    talking about as they would be marked on my DC adapter (the wire with
    the white strip being positive), not in reality, because I know that
    negative and positive are actually switched right?

    Would what side I'm putting the switches on actually make a
    difference? And for that matter, what side should the resistors go on?
    I assume it would be where the current flow originates from in
    relation to the LED, like on the positive side (which in reality is
    the negative side). Does this sound right?
     
  11. Ken

    Ken Guest

    Yeah, minus the resistor that's what i have, except the switches on
    Yeah, that's right. Each group of LEDs is connected its own switch.
    Every switch is hooked to (DC-) and every group of LEDs is hooked to
    (DC+).
     
  12. Ian Stirling

    Ian Stirling Guest

    I think you'll find that that's the way it's supposed to work.
    OR means special things.
    Searching for
    wire diode matrix
    may help.
     
  13. Yes - "3V" is the positive side of your supply, and "GND" is the
    negative.

    I don't understand what you mean by "not in reality..." - positive is
    positive, and negative is negative.

    In a series circuit, the parts can go in any order. You can put the
    resistors on either side of the LEDs, and you can put the switches on
    either side of the LED/resistor combination. The only requirement on
    position or direction is that the LED cathode must be nearer the
    negative supply, and the anode nearer the positive supply.

    The "direction of current flow" is irrelevant here.

    Most people talk of current flow as a movement of (mythical) positive
    charges from the positive terminal of the power source, through the
    circuit, and returning to the negative terminal, even though we know
    that in most materials, current is really a movement of negatively
    charged electrons from the negative terminal of the power source,
    through the circuit, returning to the positive terminal. The "flow of
    positive charge" concept is called "Conventional Current".
     

  14. If all the LED groups turn on when you turn any switch on, then things
    must not be wired as you think - you must have connections between the
    switch sides of the groups of LEDs.
     
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