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How is sequential firing in electronics achieved?

  1. Aug 21, 2012 #1
    How are light bulbs turned on and off in sequence for some signs and flat screen televisions?

    How are electromagnets turned on and off in sequence to accelerate maglev trains and coil gun bullets?

    How are the CCD arrays in electronic cameras turned on and off in sequence to transmit the captured images to the recording device through a serially transmitted electrical signal?
  2. jcsd
  3. Aug 21, 2012 #2
    For simple systems, a timer/clock pulse is generated (eg by an NE555 chip) then fed into a counter chip which will count up in binary (so for each pulse the counter will increment in binary - 0000, 0001, 0010, 0011, 0100 etc). Those binary states can then be combined via digital gates (AND/OR/NOT) to give output signals/states at specific time.

    Fancier systems like washing machines use microcontrollers

    In the olden days, it was reels with revolving contacts/bumps pressing microswitches.
  4. Aug 21, 2012 #3
    Yes, usually the counter will be implemented as a jump counter so that the electrical output can automatically be switched from one output terminal on the IC chip to another output terminal but how is this accomplished electronically within the circuitry of the IC chip? What type of electrical phenomenon makes this possible?
  5. Aug 21, 2012 #4
    There is a class of chip between microprocessor and just a bunch of gates called a multiplexer. A good example is the 8 line to 1 line 74151 IC.
    These can operate at video frequencies and above.

    These are electronic versions of the revolving contacts called actuators or contactors, which were actually pretty sophisticated and reliable so don't sneeze at them either. However mechanical systems are frequency limited to a few kHz at best.
  6. Aug 21, 2012 #5
    Yes, how does the IC chip perform the function of the electromechanical contactor but in a solid state manner?
  7. Aug 21, 2012 #6
    Depends on the application. In some cases the IC would drive electromechanical relays in other cases a transistor can be used to stick with a strictly solid state design.
  8. Aug 21, 2012 #7
    Have you googled the spec sheet or multiplexer in general?

    The following is a mid 70s circuit to put 8 channels on a single channel scope.

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    Last edited: Aug 21, 2012
  9. Aug 21, 2012 #8
    You're looking for power switches. Look up SCR, TRIAC, ignitron, MOSFET, BJT, IGBT. There are others.
  10. Aug 21, 2012 #9


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    you should also look up how a simple clock or "multivibrator" works. you can actually build a simple one with an op-amp (wired up as a Schmidt trigger), a couple of resistors and a capacitor. the timing of the period has something to do with the RC time constant.

    once you have a clock, the rest is all logic, then you need to learn how a flip-flop works. and then a "state machine". this is what you learn in your first digital logic course. you need to learn about AND, OR, and NOT gates, about truth tables, about Boolean algebra, and then about sequential state machines in general. that is when you'll first run into the concept of "microcode".
  11. Aug 21, 2012 #10
    Not really these are just signal level power requirements.
  12. Aug 27, 2012 #11
    Maybe you missed this one:
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