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Need help designing a sequential circuit

  1. Sep 11, 2013 #1
    Hi, I apologize in advance for not knowing the right terminology, I've been on wikipedia for the last two hours and my brain is mush.

    I'm trying to design a basic circuit that will cycle through multiple circuits in series. I really have no idea how to describe this, except to draw it. I know my schematic is awful, and I don't know how accurate my transistor symbols are, but I hope the gist is evident. I need a current to turn on the load at A, then when A is manually turned off by a switch, bypass it and turn on B, until B is turned off, then C switches on, ad infinitum. The only way I could think of to do this was to use transistors to force current to the load, since it will have a higher resistance than the bypass will. I know I need some sort of counter or memory circuit to do this, unless there's a much easier way that I don't understand.

    I'm decently skilled with soldering, so I'll be building this myself, but I need help designing and then picking out low cost components. Thanks in advance!

    Attached Files:

  2. jcsd
  3. Sep 12, 2013 #2


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    I'm not getting it. I see three loads bypassed by transistors, but nothing to describe the concept "B is turned off".

    Try drawing it out with relays and switches so you can avoid the biasing issues.
  4. Sep 12, 2013 #3
    Will this circuit cycle through the loads only once? The way you describe it, all the manual switches must initially be turned on. Once each one is manually turned off, this circuit would not work a second time unless all the switches are manually turned on again. Is that what you want?
    Last edited: Sep 12, 2013
  5. Sep 12, 2013 #4
    I know just enough about electronics to get myself into trouble, but not enough to do much useful, and trying to learn through wikipedia feels like trying to jump into calc3 after just finishing basic algebra. I'll try to explain my concept a little better:

    I have loads A, B, C, etc. When the circuit receives power I want A to turn on, but not B or C. When A is manually switched off, I want the circuit to automatically power B and only B until it is switched off. Once B is switched off, C should receive power until it is manually switched off. I want to be able to expand this with up to 20 loads/outputs. When the previous load is manually turned off, the next should automatically activate. I don't know the best and most compact way to do this.

    Yes, I plan on having to manually reset it, that's fine with me.

    I did some more reading, and it looks like this would be most easily done with MOSFETs, but I still don't know what component(s) to use to make a sequential switch.
  6. Sep 12, 2013 #5
    Now we need to get into some details.
    How does power get applied to the first load?
    How much voltage does each load need?
    How much current?
    AC or DC?
    Last edited: Sep 12, 2013
  7. Sep 12, 2013 #6
    I think I finally found what I need, sans a few modifications:


    The third circuit diagram down looks like what I need, except instead of cycling with a button, I need it to cycle on the trailing edge(?)/when there is no longer current going to load X.

    I'll be feeding this with 5V DC, and each load needs 3V DC and 1A.

    Thanks for your help so far.
  8. Sep 12, 2013 #7


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    As you continue on your path towards more complex and sophisticated designs, your ability to describe in English exactly will be a great advantage for you.

    When the U. S. Navy, for example, wants a new sonar system it writes an “Equipment Specification” (ES) which describes every function the equipment will perform. This document is then given to potential manufacturers/vendors. They, in turn, estimate the cost to provide the equipment and make a bid. Of course, if the win the contract, they are bound to produce the product that performs exactly in accordance with the ES.

    Consider yourself in the future, working in the above kinds of areas. You will need this “tool” in your tool kit. Download it, save it, and learn to use it so that you can clearly describe your ideas for others.


    This standard is the technical baseline for the design and construction of electronic equipment for the Department of Defense. It captures in one document, under suitable subject headings, fundamental design requirement for eleven general electronic specifications.
    263 pages, free
    http://quanterion.com/Documents/Documents.asp?ArgVal=6414 [Broken]
    Last edited by a moderator: May 6, 2017
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