3 position Switch logic

Discussion in 'The Projects Forum' started by hupa, Nov 28, 2012.

  1. hupa

    Thread Starter New Member

    May 19, 2011
    Help please, I am a digital dunce, and not at ease with logic circuits.

    I have 3 membrane buton switches each with an associated LED.
    Here is what I want....
    a) The button pressed dominates (cancels whichever of the other 'positions' was on), and latches.
    b) No strange latchups if more than one button pressed accidently.
    c) On power up a jumper determines which 'position' is on.
    d) Could your idea be extended to N positions with N buttons?
    I have supplies of +5, +12, +- 10 & +- 15 available. Load is minimal.
    Any ideas please? It seems so straightfoward, but I'm struggling, and I refuse to use a micro.
  2. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    Each LED is controlled by a set/reset flip flop. Each button will drive the SET input of it's flip flop, and thru an OR gate RESET all flip flops NOT driven by it.

    Using a diode OR scheme would allow this to be extendable to N stages.

    The power on set scheme would be similar, OR to the SET of the on device, and to the RESET of all other devices.
  3. hupa

    Thread Starter New Member

    May 19, 2011
    Thanks Ernie
    I'm off to the bench shortly, will report progress.
    Care to post a circuit?