Pls help me~! Delay circuit

Discussion in 'Homework Help' started by coolgal, Apr 12, 2010.

  1. coolgal

    Thread Starter New Member

    Apr 12, 2010
    2
    0
    Hi all, I am doing a project that required a circuit which are able to provide 15s of positive voltage and 15s of negative voltage alternately. I am using 555 timer circuit but it only give me positive and zero voltage. I cant get negative voltage.

    Does anyone have any idea on this?? can tell me how to do this??

    Really really thanks~!
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
    5,201
    312
    If you use the 555 to trigger a dpdt relay, you could switch between a +15v and a -15v power source. And actually Bill_marsden has a blog here with 555 circuits. One of them includes a 555 flip-flop. You may also use that to switch an npn and pnp transistor to switch between +15/-15v
     
  3. coolgal

    Thread Starter New Member

    Apr 12, 2010
    2
    0
    Hey, really thanks for helps.
    but I still not very understand about how to switch between positive and negative voltage by using 555. Do you have any info how to do that?
    and how to use npn and pnp?

    Thanks
     
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