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Help needed for 5 button selector circuit

Discussion in 'Electronic Basics' started by Glenn Ashmore, Apr 7, 2007.

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  1. I have a bank of 5 DPDT momentary push button switches like the kind used
    for preset frequencies on a car radio. I need a circuit with 5 outputs to
    drive some relays such that when a button is pushed it latches the
    corresponding output high and turns the other 4 off. This has got to be
    fairly simple but I just can't figure out how to do it. Any suggestions?

    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at:
    Shameless Commercial Division:
  2. Jamie

    Jamie Guest

    yes, with that kind of switch you can do it.
    on each switch you need to use the NC (normally close) contact on one side
    to maintain a constant voltage to all relays on one of the NO (normally
    open contact).
    So each Relay needs to be a DP, one pole for your use and the other
    for the Loop lock to keep the relay in.
    All the switches will be wired in series using this NC contact so that
    when ever you press one, it will open the circuit at the end of the
    string which is supplying the lock voltage on the contacts.

    So just picture the lock voltage being connected to each (NO) contact
    of each relay in parallel.
    on the other side of the (NO) of each relay, you will connect one side
    of it's own coil. This is where Coil will be getting it's energized
    voltage from to hold it on. the other Coil connection will just be tied
    to common along with the rest of the relays.
    -- Now for the activation of the relay you want --

    When you press a button, the (NC) contacts on the switch that is in
    series with the rest of the (NC) contacts of the other switches will
    open. this will cause loss of voltage in the remaining string of (NC)
    contacts and which ever relay that was locked on will now release.
    With the (NO) normally open contact of each switch, you will supply
    to each coil power on the coil side connection of the relay..
    remember i said the coil will be connected to the opposite side of
    the locking contacts on each relay? this is where you connect your
    momentary source to pull in the relay. when the relay pulls in, the
    locking contacts will maintain it and with the mechanical slowness
    of the relay returning, you should be able to release the button quick
    enough to have it put the locking source back on before the relay pulls
    If you find that the relay pulls back to soon? You can then use a
    Cap on the output of each switch that energizes the relay coil going
    to common to hold a charge. use a diode in series after that to feed
    the relay coil.
    The diode is to prevent the cap from being charged while the relay
    is locked on so that it releases quickly, and only be charged from the
    I don't have a ASCII translation program to use here otherwise, i would
    have drawn it out for you.

    personally, i would use Flip Flops with RESET and SET (RS) type.
    The (NC) would force a Reset of all flip-flops with their RESETS tied
    together, and the closer and opening of the NO contacts would be tied to
    each Flip-flop's SET pin.
    The Q outputs would reflect the state.
    The RESET and SET pins need to be pull low to high to activate.
    you would need small cap on the reset line to prevent debouncing.
  3. Chris

    Chris Guest

    Hi, Glenn. You want simple? Here's simple. Get a 12VDC supply, some
    5VDC coil DPDT relays, and 5 resistors R that have a resistance about
    1.2 times the coil resistance of the relays, and can handle the
    wattage when 12VDC is applied. Go to your junkbox and dig up 25
    diodes, and make 5 of these (view in fixed font or M$ Notepad):

    | VCC
    | +
    | |
    | .-.
    | R1| |
    | | |
    | '-'
    | |
    | o--< From SW2
    | |
    | o--< From SW3
    | |
    | o--< From SW4
    | |
    | o--< From SW5
    | |
    | .----o
    | D| RY1|
    | - C| D
    | ^ C| .--|<--<To RY2/R2
    | | C| | D
    | | | o--|<--<To RY3/R3
    | '----o | D
    | | o--|<--<To RY4/R4
    | | | D
    | .---------o o--|<--<To RY5/R5
    | | | |
    |CRY 1A| SW1 | o | o
    | ----- |=|> - - |>
    | ----- | o | o
    | | | |
    | | | |
    | | | |
    | === === ===
    (created by AACircuit v1.28.6 beta 04/19/05

    When making this, SW1 and RY1 stand for the relay associated with the
    switch you're working on, and 2 through 5 stand for the others. The
    second set of relay contacts on the relays are your outputs. The idea
    is that pressing the DPST button performs two functions. First, it
    energizes the coil of the relay (and the first relay contact latches
    it in). Then, the other part of the switch momentarily shorts out the
    other four relays, opening all of them.

    A couple of things about this circuit. It uses up quite a bit of
    extra current when a button is pressed to pay for the simplicity. But
    it's pretty much foolproof, and behaves when more than one button is
    pressed (all relays off if more than one button is pressed). Make
    sure your radio buttons can handle the current of the 5 resistors.

    Hope this does the job.

  4. Thanks! Both of those are great ideas! I was trying to think digital but
    good old hard wiring works.

    Glenn Ashmore

    I'm building a 45' cutter in strip/composite. Watch my progress (or lack
    there of) at:
    Shameless Commercial Division:
  5. ehsjr

    ehsjr Guest

    This will do it, and you can use simple SPST momentary

    +12 -+--. .------[1K]----+----+----+----+---{{{-+----+
    | e\ /c | | | | | |
    | --- [D6][RLY] [D7][RLY] [D10][RLY]
    | | |a | |a | |a |
    | | +----+ +----+ +----+
    | | | | |
    | | [SCR1] [SCR2] [SCR5]
    | | Pb1 /| /| /|
    | | ___ | | | | | |
    `----------+--o o---[10K]--+ +---------+---{{{------+--+
    | | | | | |
    | | +--->|-------+ | | |
    | | D1 | | | |
    | | Pb2 | | | |
    | | ___ | | | |
    | +--o o---[10K]------------+ | |
    | | | | | |
    | | +--->|-------+ | |
    | | D2 | | |
    | {{{ {{{ | |
    | | Pb5 | | |
    | | ___ | | |
    | +--o o---[10K]------------------{{{----+ |
    \ / | | |
    D11 --- +--->|-------+ |
    | D5 | |
    | | |
    `------+---[.1uF]------+ |
    | | |
    [1K] [10K] |
    | | |
    Gnd --------------+---------------+-------------------------+

    For SCRs you can use 511-X00602MA2AL2 from Mouser, (18 cents
    each) or anything else that will turn on at relatively low
    current, with a hold current of ~ 10 mA. Diodes are 1N4148 or
    whatever you have, and the PNP can be just about any common
    jelly bean part, like a 2N3906.

    _How it works_
    The PNP is biased on by the 1K and D11, until a + pulse through
    the .1 uF cap biases it off, briefly. That causes any SCR that
    is on to turn off. The + pulse occurs when any button is pressed.
    Whichever button is pressed gates the corresponding SCR on, which
    energizes the corresponding relay. The SCR stays on until the next
    time a button is pressed.

  6. jasen

    jasen Guest

    one set of NC switch contacts is used to cut the holding power of the other

    shown is relay m of n

    ___ ___
    | | _-v .--->ONm
    +V --o | o...o | o--->>-----~: | ---
    --+-- --+-- Vsus : ^---+-->|-.D2 |
    S1a Sna : | --+--
    |~|---+------+-------o o---< +V
    |\| `-|<-. D1 Smb
    |_|--------+--< 0V

    Vsus is derived from one set of normally closed switch contacts
    on each button all wired in series this same signal goes to all
    the relays.

    D1 eats inductive spikes, D2 protects against the case where all the
    buttons are depressed at the same time.

    A capacitor may be needed in parallel with D1 - it depends how fast the
    relays and buttons are

    note that the load current passes through all the switches,
    if that's bad use a DPST relay (or better) like this:

    high power version
    ___ ___ : ^--->ONm
    | | _-v
    +V --o | o...o | o--->>-----~: ---
    --+-- --+-- Vsus : ^------>|-.D2 |
    S1a Sna : | --+--
    N/C |~|---+------+-------o o---< +V
    |\| `-|<-. D1 Smb
    |_|--------+--< 0V N/O

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