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delay off timer circuit

Discussion in 'Electronic Design' started by Lazer, Dec 26, 2006.

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  1. Lazer

    Lazer Guest

    Hi, I have a project that I am stuck on and would be really happy if I
    got a solution.
    I have two machines that both have footswitch controls with 1/4" jacks.
    The main unit turns on when the pedal is pressed and off when it's
    released. The second unit turns on when the pedal is pressed and off
    when it's pressed a second time. What I want is an adjustable splitter
    that accepts one footswitch and has leads that plug into both units. I
    want both units to turn on together and when the pedal is released I
    want the main unit to stop and the second unit to stop after a time
    delay (variable from 1-10 seconds). Also, if the pedal is pressed again
    before the second unit has stopped, I want both units to be on and the
    second unit's off-delay restarted when the pedal is released.
    I've played with some 555 timer circuits and relays, but can't figure
    this out. The voltage on the pedals is low (<24).
    I need help!
    Anyone know a circuit that could be a solution to my problems?????
     
  2. Hal Murray

    Hal Murray Guest

    I've played with some 555 timer circuits and relays, but can't figure
    I'd probably use a small CPU, probably a PIC. You may need
    some extra just for level shifting.
     
  3. John Fields

    John Fields Guest

     
  4. Lazer

    Lazer Guest

    The pedals are just switches. Either pedal works in both units the
    same. I want them both to turn on when the pedal's pressed. When the
    pedal's released I want the main unit to go off and the second unit
    starts a delay for the off.
     
  5. ehsjr

    ehsjr Guest

    +---------------+--[RY2]---+---------+
    | | | |
    | +----|<----+ |
    | D3 | |d (c)
    | FS |<
    +12 ---+---o o---+----+--->|---+---+----g| |s (e)
    | | | | D2 | | |
    |> | | | +| \R1 |
    [RY1] [D1] [C1] /<-+ |
    | |a | \ | |
    | | | | | |
    Gnd --------------+----+--------+---+--+----+

    +--------+---o--- Ry1-1
    | | ^---------[Machine1]---+
    Machine | |
    Power +---o--- Ry2-1 |
    Source ^---------[Machine2]---+
    | |
    +--------------------------------------+


    When you step on the foot switch (FS), relay RY1
    is energized directly, and relay RY2 is energized
    via the power mosfet, which is turned on by +12
    at its gate. The +12 volts also charges C1 almost
    instantly. When the footswitch is released, RY1
    drops out immediately, but RY2 remains energized
    by the charge on C1. C1 discharges slowly through
    potentiometer R1, which adjusts how long it takes.
    When C1 discharges sufficiently, the mosfet turns
    off and RY2 drops. The normally open contacts of
    RY1 and RY2 are wired in series with the power source
    for the machines and machine 1 and machine2 respectively.

    Use a cheap N channel power mosfet, a 22 uf cap
    and a 1 meg pot. Alternatively, use an NPN
    power darlington like a TIP 120 (note the emitter
    and collector designations). Select 12 volt relays
    with contacts rated to switch the machines.

    Ed
     
  6. _________ _________ ____________
    FS ____| |____________| |__| |_________
    _________ _________ ____________
    M1C____| |____________| |__| |_________
    _________ _________ ____________
    M1on___| |____________| |__| |_________
    __ __ __ __
    M2C____| |___________| |____| |___________________________| |__
    ____ ____ ____
    Delay____________| |_________________| |__________| |_____
    ______________ ______________________________
    M2on___| |_______| |_____

    To make things clear I sketched the diagram above. (View with fixed font).
    So we see the status of FootSwitch, Machine_1_Control, Machine_1_on/off,
    Machine_2_Control, machine_2_switchoff_Delay and Machine_2_on/off. It will
    be obvious that Machine_1 simply follows the footswitch and that you will
    need two timers. One to make the Machine_2_Control pulse the other to make
    the Delay.

    From the diagram you can read that you have to trigger Delay on the trailing
    (falling) edge of FS. You have to trigger the M2C timer on the leading
    (rising) edge of FS *unless* Delay is high *and* on the trailing edge of
    Delay *unless* FS is high. As you have timers already, I give an idea of the
    logic. The circuit below should work for you.

    ||
    FS----+-----------||-----+----+----+
    | || | | |
    | .-. | |
    | | | - |
    | | | ^ |
    | '-' | |
    | | | | __
    | ----+----+ +---| | __
    | |\ |& |-----|>=|
    Delay---)---| >O---+---------------------|__| |1 |----M2C_trigger
    | |/ | +--|__|
    | | |
    | | || __ |
    | +--||---+---+---------| | |
    | || | | |& |--+
    | .-. | ----|__|
    | | | | |
    | | | - |
    | '-' ^ |
    | | | |
    | ------+---+ |
    | |\ |
    +---| >O---------------------+
    |/
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    You can use NAND gates and use the fourth gate as an extra inverter. 555
    timers require negative trigger pulses.

    petrus bitbyter
     
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