Designing a DC regulated power supply(AC to DC) that is able to display 0 to 7 digit

Discussion in 'Homework Help' started by sakuragurl, Sep 27, 2008.

  1. sakuragurl

    Thread Starter Member

    Sep 27, 2008
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    hi everyone!!!
    I have an assignment that requires us to design a DC regulated power supply(AC to DC) that is able to display the digit 0 to 7 in an LED array for indication purpose....the following are the specifications:
    1) 3 control switches for digit display
    2) Input is 240V from TNB
    3)The current in each LED is 10mA~20mA
    4)Only discrete component allowed
    5)Power indicator and necessary safety feature required.

    I am required to design the LED array by myself that can display digits....any help would be wonderful....thank you so much....my deadline is coming up soon...
     
    Last edited: Sep 28, 2008
  2. hgmjr

    Moderator

    Jan 28, 2005
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    In your statement above, I believe you mean to say that you are required to build the display even though such a display is available off-the-shelf.

    The way it is stated, it sounds like you have the choice of building the display or buying it. I am sure that would be a misread.

    You state that you are required to use discrete components only. Does that rule out the use of digital logic gates? I suspect that you mean to say that you can't use a microcontroller.

    hgmjr
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    There is another level of confusion. Is the purpose of the power supply to simply supply the displays, or must the power supply display the output voltage with the display?
     
  4. sakuragurl

    Thread Starter Member

    Sep 27, 2008
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    actually....i am suppose to design the 7 LED Display by myself...and the rest of the post was what i copied from my assignment question handed down by my sir....i really have not much idea how to carry out my assignment....
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    If it is simply a 7 segment display from individual LED's, that should present very little difficulty. What is the problem you are having?
     
  6. sakuragurl

    Thread Starter Member

    Sep 27, 2008
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    actually i do not know how to construct the entire circuit with the given specifications....like...i need to have a power supply, step down transformer, rectifier circuit, filter circuit and a regulator circuit rite? and i do not know how to use the three switches to control the numbers displayed on the LED arrays....and how do you construct the LED array to show the numbers? can you at least show me a schematic diagram to construct the circuit?
     
  7. beenthere

    Retired Moderator

    Apr 20, 2004
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    You can read out Ebook for information about rectifying your AC from a step down transformer. Here's that link - http://www.allaboutcircuits.com/vol_3/chpt_3/4.html.

    Get the data sheet on a regulator, like a 7812 to see how to wire it.

    Google for a 7 segment display to see how the LED's are arranged. That is very simple. You will need resistors to limit current in each string of LED's. Add the forward voltage of the LED's and subtract that from the source voltage, an calculate the resistor using R = E/I, where E is the result of the source minus the forward voltages, and I is the desired current.

    What do the switches do?
     
  8. sakuragurl

    Thread Starter Member

    Sep 27, 2008
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    Thank you so much! erm, the switches are for controlling the digit displayed on the 7 Segment LED. We have been given a hint that we have to make the switches work like logic gates...for example, when all switches are turned off, the digit displayed is zero...something like dat...but the problem is fixing the connection to do that...i am not sure how to fix up that connection.....by the way, what are the means of producing a good epitaxy in wafer fabrication? that is my another question for the theory part of my assignment....my assignment is due on 7th of October
     
    Last edited: Sep 30, 2008
  9. cheer

    New Member

    Sep 30, 2008
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    i have the same problem here..
    then what is the next step?
    how about your schematic, you design it already?
     
  10. mkbutan

    Senior Member

    Sep 30, 2008
    270
    16


    HI
    IAM NOT A BIG EXPERT IN ELECTRONIC'S
    BUT CAN GIVE YOUTHE BLOCK DIAGRAME OF YOUR REQ. CKT.
    AND SCTH.ALSO
    BUT BEFORE THAT I WOULD LIKE TO KNOW {THE USE OF THE 3 control switches for digit display.}
    BY THE TIME YOU REP.I WILL TRY TO MAKE THE DIG.
    GOOD LUCK
    ∏∏∏∏∏∏√
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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    Do you have to do this all from the switches, or can you use a 7 segment driver chip?

    Actually, I think this can only be done with an IC. Get the data sheet for a CD4511 7 segment driver. You will just about have to use something like it. If you are having to use TTL, get the data sheet for a 7447.
     
  12. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    your 3 swithchs are binary numbers.

    starting from the right most switch that would represent decimal 1
    middle switch rep. dec. 2
    left most switch is dec. 4

    your switch array would be 4 2 1

    all switchs off =0

    right switch on only =1
    middle switch on only =2
    right and middle switch on=3
    ect...
    all switchs on =7

    binary numb. would be all switchs off = 000
    binary 1 001
    bin.2 010
    bin.3 011
    ect...

    so you are combining switch inputs (binary) to produce single digit outputs (decimal)

    I think Thats the purpose for the switchs.

    sorry your schematic didn't show up on my computer, it came up in word pad.

    hope this helps also...
     
    Last edited: Sep 30, 2008
  13. sakuragurl

    Thread Starter Member

    Sep 27, 2008
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    0
    Thanks...that really helps....but do you have a sample schematic diagram to show how do we connect the switches to the LED array??? i am not allowed to use an IC chip unfortunately...asked my sir already but he said we can't use it....is there any other way??
     
  14. beenthere

    Retired Moderator

    Apr 20, 2004
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    Perhaps with steering diodes. As this is a homework assignment, maybe you could impress us with a bit of effort here. Arrange the display as common anode and let the switches connect to ground. That is a set of big hints. Try some experimenting with individual LED's.

    Don't forget to place a current limiting resistor in series with each set of LED's.

    Post up some circuit arrangements you think might work - for the LED's and the switches.
     
  15. hobbyist

    Distinguished Member

    Aug 10, 2008
    764
    56
    hi
    Are you sure sir wants you to make a decimal output for all the decimal combinations 0-7 on a decimal display, because if he is then you must have learned how to design transistor "inverters" and "AND" gates, otherwise maybe were misunderstanding your assignment, because the way I made mine was making transistor logic "AND" gates and transistor inverters, and arranging the whole complex to be able to input the switch combinations and output a single output to the display and then combining the proper leds in the display to show a decimal number.

    Again if you are using combinations of these three switchs you need a way to be able to isolate the outputs from each other with every input of each switch. Probably sounds confusing maybe someone can better explain it. what i'm trying to convey here.

    example, if you hit switch 1 then you can take that output signal and combine the 2 right leds on the display.
    (each one having it's own limit resistor.)

    now input switch 2. again you connect the proper leds on the display to show dec. 2.

    NOW if you hit switch 1 and 2 together, you need to CANCEL the individual outputs of switchs 1 and 2 and produce another output signal to be able to combine leds, to show dec. 3.

    The way this is done is through inverters and "AND" gates (logic gating) using discrete components. So unless you have learned how to design logic circuits from discrete components than maybe your misunderstanding what needs to be done with these switchs and the circuitry involved.

    That's the only suggestion I have about this.

    Maybe someone else has a idea of how this could be done without logic gating. I don't know...

    Could it be he wants you to make the decimal numbers 1-2-3 only, then you only have to use as the other gentleman said steering diodes and limiting resistors which means the three switchs would be individully used and NOT combined for any other numbers.

    that sounds more feasible I think..

    Hope this helps somehow...
     
    Last edited: Oct 1, 2008
  16. sakuragurl

    Thread Starter Member

    Sep 27, 2008
    14
    0
    actually...i get the main idea about the switches....however, i have not learnt about transistor "inverters" and logic gates yet...i dun even understand why our sir is giving us this assignment when we do not know how to do it and we can't use IC at all....thanks for your help anyway....i will try using logic gates...i really appreciate your help...thanks!
     
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