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Sequential Switching Circuit

  1. Sep 29, 2009 #1

    About the Sequential Switching Circuit, it can be made from four 555 timers.I have no idea about how the 555 timers work in the sequential switching circuit?From what I have searched in wiki, I still don't understand how the 555 timer work.Can somebody explain to me?

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  2. jcsd
  3. Sep 29, 2009 #2


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    That circuit uses four 555 chips as Monostables.

    Each one is triggered by a falling voltage on pin 2.
    This produces an output on pin 3 which goes from zero volts to 5 volts, stays there for about 5 seconds and then falls back to zero volts.

    When it falls, this change is passed through the capacitors to the next 555 and that then gives another 5 second output pulse.

    The 5 second time is controlled by the 5uF capacitor and 1 M resistor on each chip connected to pins 6 and 7. Making either of these bigger will increase the time. Making them smaller will reduce it.

    When each output is high it is used to control a relay, although probably not directly.
  4. Oct 1, 2009 #3
    Thanks!But I still confuse on how is the input going to be? I have construct this circuit and by using a wire to connect the part of switch which is connected to the first timer.LEDs are connected after the relay from pin 3.Those LEDs light up at the same time and not light up in sequent.How can it like that?

    Does this problem occurs because of switch part( replace by wire ),and what switch should be used(push button or on/off button)?How does the switch affect the output?

    For the 5 second output pulse do you mean of the LED will light up for 5 second?
  5. Oct 1, 2009 #4


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    Pin 3 should rise to 5 volts and stay there for 5 seconds and then fall to zero after you push the switch.
    This should happen to each 555 in sequence.

    If it doesn't, you need to get each stage working one at a time.
    Remove C3 and concentrate on stage 1.

    Measure the output on pin 3 of the first stage with a meter, without the LED.
    If it doesn't behave as it should, check that you have wired it correctly.
    It is a standard circuit, so it should work OK.

    Is your 1 M resistor really 1 M ? It would have the following colors brown, black, green.
    And the capacitor should be 5 uF. Does it actually say that on it?

    Compare it with this circuit in Wikipedia.

    Take a picture of it, if you like, and send it here, but you should be able to find out what is wrong with it, yourself.
    Last edited: Oct 1, 2009
  6. Oct 1, 2009 #5
    how want design sequential switching circuit by only being provided a 0.1uF, a 5uF, a 0.01uF capacitor, a 10k ohm and a 1M ohm resistor? And I want ask about the use relay, they supply 4 relay..?
  7. Oct 1, 2009 #6


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    Hi MTBAR. Welcome to the Forum.

    how want design sequential switching circuit by only being provided a 0.1uF, a 5uF, a 0.01uF capacitor, a 10k ohm and a 1M ohm resistor? And I want ask about the use relay, they supply 4 relay..?

    There is an English problem here, but if you only have passive components, ie no 555, you will have problems developing a sequential switching circuit. I can't see any way of doing it.

    The relays in the current circuit would turn on in sequence over a 20 second period. There is an interesting possibility that you could bring the final stage output back to the input and have the relays cycle around continuously until the power is removed.

    The number of relays is optional, but you would need one 555 stage for each one.
    Each would probably need to be switched with a switching transistor rather than directly from the 555 as shown.
  8. Oct 2, 2009 #7
    how to connect pin 3 of 555 chips with the relay? My reason do not see connection of relay, relay prepared be 5 pin?

    please help me vk6kro...
    Last edited: Oct 2, 2009
  9. Oct 2, 2009 #8


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    You would need a relay driver. I have sketched the simplest of these, but they can get a lot more complex than that.

    Try Google for "relay driver".

    Mostly it depends on the current it takes to turn the relay on and how much drive current you have available. These two figures tell you how much gain is needed in the driver circuit.

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