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Turning a light on and off with momentary switch

Discussion in 'Electronic Basics' started by Chris W, Feb 16, 2005.

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  1. That's great - thank you sincerely. It appears fairly simple and I look
    forward to trying to implement it.

    This is my first time reading a schematic in ascii, and it mostly makes
    sense to me. My only question is what does "O" represent? For example,
    there is an "O" next to CP1. Thanks for your patience.

    Regards,
    Peter
     
  2. Thanks for the tip. I have used a 555 timer before, but I don't think I
    ever used it as a one shot circuit, so I'd have to look that up.
    Thanks - I think that's exactly the approach that John Fields took in his
    schematic (see other posting in this thread).
     
  3. Guest

    Thanks - I think that's exactly the approach that John Fields
    Yes, except for the extra transistors which will allow
    much more current for brighter LEDs. If you hook the LEDs
    directly to the 4017 with a resistor, you only get 2 or 3
    milliamps. The extra transistor will get you 20 mA or more.

    -Bill
     
  4. John Fields

    John Fields Guest

    ---
    The 'O' is used to represent what's called a 'low true' input. That
    is, a desired result occurs as a result of that input being at a
    logical '0'. In this case, that's zero volts or 'ground'

    The other "O"s (at the switch) are just a convention used to denote a
    switch (or relay) terminal.
     
  5. John Fields

    John Fields Guest

    ---
    Well, in all fairness, Bill's is better than mine in that he has a
    single current limiting resistor as opposed to my three. Since only
    one LED will be lit at any given time, there's only a need for one and
    it can be connected from the common cathodes of the LEDs to ground.

    He's suggested using a 555 to debounce the switch, but my simple RC
    may work just as well. Depends on the switch's bounce
    characteristics.
     
  6. Rich Grise

    Rich Grise Guest

    What's your goal here? To learn about flip-flops, or to turn a light on
    and off? If the latter, just get a push-on-push-off switch. PCs used to
    have them - it's a mechanical action, a la a clicker ballpoint pen.

    Cheers!
    Rich
     
  7. Harold Ryan

    Harold Ryan Guest

    Hi Chris:

    The circuit that you want to build consists of three sections. (1) The
    momentary switch must be connected to a debounce circuit. This will create
    only one edge when the switch is closed or opened. This is accomplished by
    using a resistor and a cap to create a lowpass filter and a buffer logic
    device like a 'AND' gate. The secret is to use an additional feed back
    resistor that creates hysteresis.

    The second section is the flip-flop that is wired to toggle. U can use a
    74HC74 D type flip-flop or even a JK flip flop. The 3rd section is the
    decode logic. If you want to just toggle an LED then there is no decode
    logic. Just connect the output of the flip-flop to an LED or thru an
    additional buffer chip. If you want to have 3 LEDS to sequence, just add
    another flip-flop and use a couple NAND gates to decode the two outputs of
    the two flip flops to generate 3 outputs. Use 74HCXXXX chips because the
    crossover threshold voltage is 5volts/2 or 2.5 volts.

    Harold
     
  8. Great explanation! Thank you for providing an architectural synopsis of
    what's involved.
    Peter
     
  9. Yes, except for the extra transistors which will allow
    That's helpful, since I do not yet know the operating characteristics of the
    LEDs that I will want to use.
    Thanks,
    Peter
     
  10. ---
    For me, there is educational value in seeing multiple approaches to the same
    problem, particularly when someone explains the difference between the
    various approaches, as you just did. So thank you.

    Would you (or any other reader without commercial bias) please recommend an
    inexpensive and reliable vendor for electronics parts for projects such as
    this one? If such recommendations are not allowed on the newsgroup, please
    feel free to email them to me.

    Thank you,
    Peter
     
  11. Here are my links to electronics distributors (US bias)

    http://www.acroname.com/
    http://www.allcorp.com/
    http://www.alliedelec.com/
    http://www.aade.com/index.html
    http://www.sciplus.com/?emailid=25
    http://www.bgmicro.com/
    http://store.yahoo.com/webtronics/index.html
    http://www.componentkits.com/
    http://www.elexp.com/
    http://www.findchips.com/
    http://www.futurlec.com/
    http://www.jameco.com/
    http://www.thelaserguy.com/index.html
    http://www.mcminone.com/
    http://www.meci.com/
    http://www.mouser.com/
    http://www.moyerelectronics.com/
    http://www.mpja.com/
    http://www.probemaster.com/
    http://www.quickar.com/about.htm
    http://www.quickar.com/index.php?session=
    http://www.goldmine-elec.com/
    http://www.commlinx.com.au/timing.htm
    http://www.electronicsurplus.com/
    http://alltronics.com/wire_and_cable.htm
    http://home.att.net/~wzmicro/index.htm
    http://www.alltronics.com/
    http://www.lsdiodes.com/5mm/
    http://www.hosfelt.com/

    I usually use goldmine or futurlec for hobby parts. They don't mind
    small orders, and don't charge me sales tax (I'm in california)

    You can also get samples of parts from distributors like microchip,
    analog, linear, national, fairchild, etc.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
  12. For another possibility, try this link:

    http://home.comcast.net/~rcmonsen/flipper.GIF

    I built a circuit nearly identical to this one, which I control with a
    small 40MHz radio control. The main problem I have is that the radio
    control (which I swiped from a toy car) gets occasional hits, which
    trigger the device without warning. I have it hooked up to a large,
    lighted, mechanical pink flamingo that my wife decided she needed (and
    which was on sale for 1/2 price!). Thus, it goes on occasionally by
    itself, which is actually kinda fun.

    The circuit itself is really just an inverter flipflop, like this:

    R1
    ___
    .---------------|___|---------------------------.
    | |
    | U1A U1B |
    | R1 |
    | |\ ___ |\ |
    '--------| >O---|___|----------o----| >O----o---'
    |/ | |/ |
    \ o |
    S1 \ |
    \. |
    o |
    | R2 |
    | ___ |
    o----|___|---'
    |
    --- C1
    ---
    |
    GND

    (created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)

    except the inverters are NPN common emitter amplifiers instead of
    inverters. IF you close the switch for a moment, the inverter U1B
    changes state, thus changing the state of the other inverter. If R2 >>
    R1, then even when the button is pressed, it won't oscillate. The cap C1
    must be large enough to allow the input of U1B to reach it's switching
    threshold for long enough to switch, despite the action of R1.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
  13. Thanks for the list of resources, annotations, and candor regarding your
    bias :)
    Peter
     
  14. Si Ballenger

    Si Ballenger Guest

    The below LED chaser kit for $6.50 would give you most of what
    you want. A momentary push button, a 10k resistor and a 1uf
    capacitor in parallel to ground for debounce should be sufficient
    for manual operation instead of from the 555 timer.

    http://www.allelectronics.com/cgi-bin/category.cgi?category=305&item=AEC&type=store
    http://www.allelectronics.com/spec/AEC.pdf
     
  15. Guest

    Would you (or any other reader without commercial bias) please
    Well, you could try Radio Shack, but they seem to have less and less
    parts available nowadays.

    For mail order, I can think of three, but they may require a minimum
    order.

    www.digikey.com
    www.jameco.com
    www.mouser.com

    Also, I have a few items for sale on my
    website which may be of some use.

    http://ourworld.compuserve.com/homepages/Bill_Bowden/sale.htm
     
  16. That looks like a handy circuit that could be adapted to my application. I
    might fiddle around with it and compare to the others. Thanks.

    Do they sell any kits for this that include the mechanical pink flamingo?
    :)

    Peter
     
  17. Sadly no. The R/C pink flamingo is destined to remain one of a kind.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
  18. Rich Grise

    Rich Grise Guest

  19. That is totally high class. The one I got was built out of pink mesh
    screen. Only the neck and body move. However, it has several strings of
    LEDs in it that flash on and off. It's eyes also flash, if I remember
    correctly.

    --
    Regards,
    Robert Monsen

    "Your Highness, I have no need of this hypothesis."
    - Pierre Laplace (1749-1827), to Napoleon,
    on why his works on celestial mechanics make no mention of God.
     
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