Storing a value with npn transistors

Discussion in 'The Projects Forum' started by shaqywacky, Jan 16, 2011.

  1. shaqywacky

    Thread Starter Active Member

    Apr 1, 2009
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    Is there a way to store a value with npn transistors. By storing values I mean if you give it voltage it goes high and stays high until something else makes it go low, then it stays low. I can do this with relays but I am very angry at relays right now and I would like to eliminate them from my project(the same one I was working on in the last thread I made).

    Also, It pains me to ask this but in this thread, I was using relays and some smart person suggested that I not use relays, but I was like "bUt i LIek rELayS!!1". So if it isn't too much to ask: How would I do that without relays?

    Thank you!
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Look up set reset flip flops.

    [​IMG]

    Ground a collector, the flip flop switches, and will maintain that state until the other collector is grounded. This is the basic memory cell for digital memory, one bit.
     
    shaqywacky likes this.
  3. shaqywacky

    Thread Starter Active Member

    Apr 1, 2009
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    Thanks Bill, that's perfect.
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Here is another method. Something I reinvented a while back, before finding other older versions of the same circuit elsewhere. So much for my claim to fame.

    555 Bistable Multivibrator
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Just for giggles, I simulated the circuit Bill posted.

    See the attached.

    A few caveats:
    1) It's fine to short the collectors to ground - however, you must not attempt to short them to Vcc or you will fry the transistor.
    2) When the power is first applied, the Q and Q\ outputs will be in an indeterminate state (not a logic 1 or 0) until the first S\ or R\ is applied.
    3) With the resistor values I used, current flow will always be at least ~10mA. This makes it not very suitable for a battery-powered application.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    You can also short the bases. It is Vcc that gets you into trouble.
     
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