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555/556 TIMER

Discussion in 'Electronic Basics' started by DaveK, Mar 11, 2007.

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  1. DaveK

    DaveK Guest

    I'm using a 556 Timer and want to do the following with it:

    When the external Mercury switch of the 1st timer on the 556 is closed
    then opened it will sound a Buzzer for approximately 2 sec. At the
    same time it will supply power to the 2cd timer of the 556. When the
    second external Momentary switch is closed and then opened it will
    turn on a LED. The LED will continue to stay on till the fist Mercury
    switch is activated once again, which starts the cycle over again.
    I hope this make some sense, especially since I am new to all this.
    I would surely appreciate it if anyone could make up a schematic or
    something to get me going in the
    right direction. Please contact me if more information is needed.

    Thank You for Your Time,

  2. Jamie

    Jamie Guest

    ok, so i guess you could use a one shot timer on the first one via the
    use of the Reset, use it's output to release the reset line of the
    second one, use the
    second switch to set the trigger of the second timer which should
    if memory serves switch on the output of the second timer..
    this output can run an LED etc..

    so basically, you want a momentary latch of your second switch
    only while the first one has tripped the timer for no longer than
    2 secs or so..
    and when the first timer expires, it should also kill the
    output of the second timer and hold down the reset ..
    i guess i was to think about it some more it would be simple.
    I would think a Data type flip-flop from the first timer would
    do what you want.
    oh well.
  3. DaveK

    DaveK Guest

    Thank you for your quick response.

    If I had the buzzer only come on while the 1st switch is close would I
    even need a timer? If that's the case how do I give power to the
    second switch, which when closed turns on the LED till the first
    switch closes again? Remember the first switch is a momentary switch
    and may close for different periods of time. Would I even need a timer
    for the second switch? How could I accomplish this? I don't know
    anything about flip-flops or latches, if something like that would
    even work. If you can give me any information along with part numbers
    or schematic showing how it would work I would surely appreciate it.

    Thank You,

  4. DaveK

    DaveK Guest

    Thank You so much for all the information, I hope it did'nt take you
    to long . Where did you get your smarts from? I'm going to go through
    this and try some stuff out. If you don't mind, I will probably need
    to contact you again. Your a great help! Thanks!
  5. Jamie

    Jamie Guest

    ok, some more info is needed his.
    If i read you correctly. I think what you need is a
    is a data flip flop.
    Look about half way down on this page and read alittle about

    Basically, you have a Data input, this would be for example your switch 2
    then you have a C (clock) input, this would be from your switch 1..
    depending on the type of D-FF you want to use.
    for example, the C input (clock) goes from low to high using your
    switch 1, it will take what ever state the D (input) is in and place
    that to the Q output and thus hold that state until the next time the
    C input gets a low to high transition input, which will repeat the
    process over again.
    the Q output can be used to light up an LED if you wish.
    now when i said there are different kinds of data flip-flops? i meant
    there are different types of triggering styles
    for example.
    the one i just used would be a Positive edge which means that it takes
    the D input status and transfers it to Q when the C (Clock) goes high.
    so that means while the C is being held to low (common), the Q output
    holds the current value that was there before.
    Now, if you used a negative edge type, it will capture the state at D
    and transfer that to Q when C goes low (ground).
    both edge types ignore changes taking place at D while
    the C input is being held at the trigger level.
    this means, it will only capture what D is at the time of transition
    of the CLOCK level change per type that your using.

    Now, you have level type D-FF's, and they have high capture
    logic for the CLock, and what this means is, while the Clock is in
    the high state, Q will reflect all activity of changes from D until C
    goes back to the low state at which point Q holds the last state of D..

    I hope you understood that and i didn't get anything twisted here.

    I noticed that the sight i gave you has their description of the level
    type miss leading. I double checked some doc's i have here to make sure,
    they state that Q holds the last value until C goes low, that wouldn't
    really make sense because why would you need a Negative edge FF ?, so
    the statement there is a little incorrect, D will show at Q it's value
    while C is high, and when C goes low, Q will hold the value at
    transition time.

    Basically, if your attempting to create some synchronizing circuit
    where you need an output to appear when switch 1 is on and switch
    2 is on to show that you have sync, this would be the way to do it.
    because the next time
    also remember that you will need a deboucer on the Clock input
    because if you have a poor connection there, it will trip that input
    multiple times.
    if you plan on using a contact switch, i would suggest using a small
    capacitor on the input to common. something like a 0.01 uf..
    Also, if you require a minimum time for Switch one to hold it's
    state? you can adjust the cap size on the clock input.
    just remember to select the type of flip flop you need and to drive
    an LED, use a TTL type.
    the 74xx series is good for that. other wise you will need driver
    Like many other Flip Flops, many have Set and Resets..
    all this means is, you can force the Q output to what you want at start
    up if you wish..

    A positive Edge D-FF
    One with 8 D-FF's with common Clock for all.
    A list of Quads etc..

    they come in different varieties, just remember the 74xx, 74xxx series
    are TTL which can handle the current of the LED and is 5 volt logic etc..
    other types are static sensitive.
    the 74HCxxx series allow for a wider range of supply voltages.
  6. Rich Grise

    Rich Grise Guest

    They paid attention in class, and read a bunch of books and stuff.

    Good Luck!
  7. Rich Grise

    Rich Grise Guest

    Sorry - this was a little harsh for the .basics group. I'll try to cancel
    the post. I've broken the fundamental rule of s.e.basics - the only dumb
    question is the one you don't ask.

    But, it does sound kind of like you're looking for an R-S flip-flop for
    your second stage.

    Have Fun!
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