30 min clock shutoff

Discussion in 'The Projects Forum' started by shaqywacky, Dec 1, 2010.

  1. shaqywacky

    Thread Starter Active Member

    Apr 1, 2009
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    I'm having a weird problem, I made a circuit to turn off the LEDs in my clock for 30 mins. The timer works fine but to turn off the LEDs I need to connect two pins on the 7-segment display set. When I connect them directly the LEDs will turn off. But when I connect one side to a transistor and the other side to the other side of a transistor and give the base power, they still act like they're not connected.

    At first I thought that the transistor had too much resistance but eventually eliminated that.

    I wrote a long post deeply describing the situation but I felt like it would make things more confusing.

    If you need more info I can post it.

    Attached is the diagram. I know I that I did a triple inverter but I did it because it made it less confusing for me.

    I'm thinking that there's something about transistors that I don't fully understand that is causing my problem.

    Thanks for any suggestions.
     
  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    718
    Are the LEDs in the 7 segment display common cathode or common anode?

    You have the "To LED" grounded.
     
  3. iONic

    AAC Fanatic!

    Nov 16, 2007
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    I assume that D2 represents the LED segment and not just an indicator LED.
    I'm not sure why you need 2 Transistors from the 555. Does the OP need both?


    iONic
     
  4. shaqywacky

    Thread Starter Active Member

    Apr 1, 2009
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    0
    That is just showing where my circuit ends and the clocks circuits start. So that whole line is meant to symbolize the two ends of whatever it is I'm connecting. Just imagine its the power to all the LEDs in the segment. I really don't know what it does.

    I'm not sure right now, I'll check in a little bit, I'm a in a rush right now.

    @iONic D2 doesn't represent the LED segment, I just put in in to make sure it worked.

    and no I don't need the two transistors, I just did it to make it clearer for me.
     
  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    If shorting the wire where the transistor is disables the display, and the transistor doesn't replicate the function, it may be you need a PNP transistor and supporting circuitry rather than the NPN.

    Can you post a photo of both sides of the circuit board, then annotate another photo for where you are modifying it?

    There may be a simpler way to go about this, but I can't say for sure.
     
  6. radiohead

    Active Member

    May 28, 2009
    474
    31
    try using a relay
     
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