Help needed in Flip Flop

Discussion in 'The Projects Forum' started by vivek_pv, Aug 4, 2006.

  1. vivek_pv

    Thread Starter New Member

    Aug 4, 2006
    2
    0
    Hi all,

    I have a single blink type of signal (+5V) with this I need to switch on an LED unless one switches it off (resets it).

    Please tell me how it can be done with Transistors (or F/f IC).

    Thanks,
    v
     
  2. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    You only need a resistor and the LED.
     
  3. vivek_pv

    Thread Starter New Member

    Aug 4, 2006
    2
    0
    But how?

    I want to hold the light "on", even when the signal went "off".
     
  4. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi,

    you can do it with an SCR.

    moz
     
  5. ttennis

    New Member

    Aug 16, 2006
    3
    0
    Do you mean that you would like an LED to come on and stay on when you use a 5V signal to set an FF?

    If that is the case, you can use two cross coupled transistors to form a latch. Use the Q output to drive another transistor that has the LED in its collector circuit. The LED will light when you momentarily apply 5V to the SET input. It will go out when you apply 5V to the RESET input.

    Alternatively, you can use a TTL flip flop such as a 7474
     
  6. nomurphy

    AAC Fanatic!

    Aug 8, 2005
    567
    12
    See latch circuit below for one example:
     
  7. pebe

    AAC Fanatic!

    Oct 11, 2004
    628
    3
    I agree with Mozikluv. You only need an SCR with the LED and a series resistor as its load. Trigger its gate to turn it on, and use a N/C push button in series with the LED to turn it off.
     
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