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looking for a 555 timer circuit

Discussion in 'Electronic Basics' started by Wayne, Jan 22, 2006.

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  1. Wayne

    Wayne Guest

    I'm looking for a circuit that would utilitize a 555 or similar that
    will have 3 120VAC outputs that it alternates between. This would be
    used to drive 3 powerheads (water pumps) on a fish tank to create some
    wave motion in the water. I would think that the time it alternates
    could be varied based on a rheostat. Also, if possible, I want to have
    a pushbutton that would stop all 3 pumps for 30 minutes or so for
    feeding (push the button, power is killed for 30 minutes to the pumps,
    then they startup again automatically). So, probably would be 2
    circuits. Anyone have a design for something like this or can help?

    TIA
     
  2. Rich Webb

    Rich Webb Guest

    Although the guys for whom solder is a favorite programming language may
    have different ideas, I'd do this with a small microcontroller. One A/D
    port to read the rheostat, a digital port to sense the pushbutton, and
    three digital outputs to control the power to the pumps.

    Could probably be done with an 8-pin ATtiny15 (same size as the 555)
    which has an internal oscillator, a couple of timers, and four A/D
    channels plus the rheostat, pushbutton, relay drivers, and relays.
     
  3. Wayne

    Wayne Guest

    I'm looking for the solder version :^) I have most of the parts on
    hand to build this, just not the knowledge of where to put the parts.
     
  4. Rich Webb

    Rich Webb Guest

    Take a look at the "555 Designer" at:
    http://www.schematica.com/555_Timer_design/Timer_Comparison.htm The
    "Pro" version isn't very expensive and has some helpful "wizards" that
    will at least give you some ideas, including I/O circuits, long interval
    timers, variable timers, and so on.
     
  5. Bob Monsen

    Bob Monsen Guest

    555 -> 4017 -> 2N4401 -> relay coil. Set up the 4017 so the Q3 output
    resets it. Also, use one of the timer-counter chips, like a 4541, to
    inhibit the entire circuit using yet another relay for your 30 minute
    pause...

    The datasheets for these chips and transistors are freely available, and
    usually have application schematics in them that are close to what you are
    interested in. If you need more help, post again.

    Note that you'll need a DC supply for the logic, which won't run on AC.

    --
    Regards,
    Bob Monsen

    "I cannot persuade myself that a beneficent and omnipotent God would
    have designedly created parasitic wasps with the express intention of
    their feeding within the living bodies of Caterpillars."
    -- Charles Darwin
     
  6. Wayne

    Wayne Guest

    Would something like this work: I'm looking at the samples shown on
    http://www.uoguelph.ca/~antoon/gadgets/555/555.html. I was thinking of
    using the '10 minute timer' to power a second circuit consisting of the
    '555 timer tester'. Instead of powering the red LED in the timer
    circuit, I would have that power the tester circuit. In the tester
    circuit, I would substitute solid state relays for the LEDs. Is this
    feasible?

    Assuming so: The timer circuit isn't exactly what I want, but close.
    Can someone show me what to change to make it 'default' to power on
    (across the red LED), and how do I calculate what value of resistor to
    use in place of the 500k resistor to get approximately 30 minutes of no
    power across the red LED?

    In the tester circuit, if I substitue a pot for R2, would this allow me
    to adjust how long the relays would be powered? I would want equal
    times (or as close as possible) of about 30 seconds on and 30 seconds
    off. Ideally, I would want 3 outputs instead of 2, but this is a
    start.

    Hope this makes sense, and thanks for any help anyone can offer.
     
  7. Deefoo

    Deefoo Guest

    Why? Fish can't eat when there are waves?

    --DF
     
  8. Wayne

    Wayne Guest

    haha. They can, but corals and some slower moving fish/creatures in
    saltwater environments need more time to catch food before it's
    filtered out.
     
  9. John Fields

    John Fields Guest

    ---
    I'll help you, but I don't understand the pump timing. In your
    earlier post you said that you want the pumps to turn on
    sequentially, which I took to mean one at a time, like this:
    _____ _____ _
    PUMP 1 __| |____________| |___________|

    _____ _____
    PUMP 2_________| |____________| |_______

    _____ _____
    PUMP 3_______________| |____________| |_


    However, above, you said that you want the pumps to be on for half
    the time and off for half the time, so you'd be talking about
    something like this:
    _____ _____ _____ ____
    PUMP 1 __| |_____| |_____| |_____|
    _____ _____ _____ _____
    PUMP 2 |_____| |_____| |_____| |__
    _ _____ _____ _____
    PUMP 3 |_____| |_____| |_____| |____

    where more than one pump would be on at a time, and the circuit
    would be much different than for the first case.
     
  10. Rich Webb

    Rich Webb Guest

    An alternate approach that might turn out to be easier if you persist in
    your perverse dislike of microcontrollers (insert smilies here as
    required to assist any humor-impaired readers) is to drop back to an
    older method of implementing long period timers: motors, gears (or
    belts), and a cam shaft. Think of a music box or washing machine timer.

    There would still be a 555 but this time (no pun intended) as a PWM
    generator that controls the speed of a small DC motor. The motor,
    through suitable gearing, turns a cylinder through one complete rotation
    every "wave cycle." High spots on the cylinder press against
    microswitches that in turn actuate the relays that handle the high
    current needed for the main water pumps. Fine tune the rotation period
    with a standard 555 PWM circuit.

    The half-hour feeder timer could be a similar gizmo. Turn it to the
    starting position that shuts a microswitch controlling a double throw
    relay. The NO position of that relay would run another motor (and 555
    tuner if required) until it reaches the low spot which opens the
    microswitch, opens the relay, and stops the motor. The NC position would
    be in the power path for the water pumps. While it's open, the pumps are
    off. When the half-hour relay drops out, those contacts shut again and
    the pumps start up.

    With the cam setup, it would also be pretty easy to cut more complex
    wave profiles with, e.g., more dwell time for the pumps on either end of
    the tank than the one in the middle, simulating (roughly) simple
    harmonic motion that "sticks" more at the extremes and moves more
    quickly through the center.
     
  11. Wayne

    Wayne Guest

    John,

    No, you are correct. What I want is what you show in the first timing
    sequence.
     
  12. John Fields

    John Fields Guest

    ---
    OK, it's on alt.binaries.schematics.electronic under "Looking for a
    555 timer circuit".

    The outputs are positive true and should be able to drive a
    solid-state relay each.
     
  13. Wayne

    Wayne Guest

    John,

    Thank you. I'll build this over the weekend and let you know how it
    works!
     
  14. John Fields

    John Fields Guest

    ---
    You're welcome. :)

    Just as an aside, you can use a 4020 or a 4024 instead of the 4060
    that's on the drawing, as well as the HCMOS (74HC40XX) versions
    (preferred) if you happen to have them around.

    If you get into trouble and you need to do some troubleshooting to
    bring it to life, here's how it's supposed to work:

    U1 is a 7555 (CMOS 555) wired as a free-running 50% duty cycle
    astable multivibrator, and it supplies clocks to U2 and U4 all the
    time.

    Pressing S1 momentarily will RESET U4 and the RS latch, U3B-U3C,
    forcing u2-1 low, which will keep the outputs of U2 low (and the
    motor driving relays inactive) until U4 times out.

    U4 times out after counting 64 low-going clock edges, and when it
    does, U4-4 goes high, SETting the RS latch and forcing U2-1 high.

    U3A is a 2-input NOR gate, and since U2-2 and U2-7 are being forced
    low while U2-1 is low, U3-1 and U2-4 will be forced high until the
    first high-going edge of the clock gets to U2-9 after the latch is
    SET by U4 timing out.

    When that clock pulse gets to U2 it shifts the high on U2-4 to U2-2,
    enabling OUTPUT1 _and_, forcing U3-1 low. U3-1 going low will
    cause U2-2 to go low and U2-7 to go high after the next high-ging
    edge of the clock. Since U2-7 will now be high, U3-1 will stay low,
    and the next clock will make U3-2 low, U3-7 low, and U3-10 high,

    Now, since U3-3 and U3-2 are both low, U3-1 will be high and the
    three-phase cycle will begin anew with the next clock:

    _ _ _ _ _ _ _ _ _ _ _ _ _ _
    CLK _| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_
    _____________________________________________________
    U2-1 __|
    ___ ___ ___ ___ ___
    U2-2 ____| |_______| |_______| |_______| |_______|
    ___ ___ ___ ___
    U2-7 ________| |_______| |_______| |_______| |_______
    ___ ___ ___ ___
    U2-10____________| |_______| |_______| |_______| |___


    Finally, since you said you wanted about a 30 second 'ON' time for
    each motor when the thing is operating and about a 30 minute pause
    when you hit the PAUSE switch, that means there will be 1800 seconds
    in each pause period and 30 seconds in each active period.

    If we make the period of the clock 30 seconds, then the total number
    of clocks we'll have to count up to get the 30 minute pause will be


    1800s
    n = ------- = 60
    30s

    Which is pretty close to what U4 counts up to, 64, so if you use the
    pot to adjust the motor ON times to 30 seconds, the pause time will
    be:


    t = 30s * 64 = 1920s = 32 minutes.

    Not bad.
     
  15. John Fields

    John Fields Guest

    ---
    Aarghhh!!!

    I just saw how to get rid of the 7555.

    Use S1 to RESET the 4060 and the rest of the circuit, and then when
    S1 is released, use the 4060's front end for the oscillator it's
    supposed to be. Then use its LSB to drive the '175 and use its Q9
    to drive the latch. Or something like that. I'll work it out and
    post the new schematic tomorrow.
     
  16. Wayne

    Wayne Guest

    John,

    Is C1 100 F, or should it be 100 uF?
     
  17. John Fields

    John Fields Guest

     
  18. Wayne

    Wayne Guest

    Ok, I'm holding...
     
  19. Wayne

    Wayne Guest

    Got the update. RevB is much cleaner. Thank you for doing this.
     
  20. John Fields

    John Fields Guest

    ---
    You're welcome. :)

    In going over the circuit for the last time, (LOL) I found a few
    errors:

    1. U2-5 should be connected to U1-3, not U1-1

    2. C1 should be an 0.18µF polyester cap.

    3. R1 should be a standard 2 megohm +/- 5% 1/4W carbon film
    resistor.
     
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