debounced SPDT switch

Discussion in 'General Electronics Chat' started by count_volta, Aug 15, 2010.

  1. count_volta

    Thread Starter Active Member

    Feb 4, 2009
    435
    24
    Hi, I am working on a project, and have noticed that switch bounce is a serious problem in my design. My design needs SPST and SPDT switches. I know how to make a simple debounced switch. The image below.

    [​IMG]

    This uses an SPDT but the end result is a debounced SPST switch. Its either high or low.

    What I need is a debounced SPDT switch. I mean I dont want the output of the switch to be either high or low, what I need is for one part of the circuit to be connected when the switch is open, and another part to be connected when its closed. You know the reason why people use SPDT switches. But I need a debounced SPDT.

    Is there a way to alter the above schematic, or is there already a schematic out there. I have not been able to find one.

    Thank you.
     
  2. blueduck577

    New Member

    Aug 11, 2010
    2
    1
    Whats up ECE 501. I remember this picture from that lab haha. Dr. Levitan is one of the coolest dudes ever.

    This circuit provides logic levels. You should look into the CD4053 analog multiplexer IC. Basically it is a SPDT switch that is controlled by logic levels. You can use the above circuit to debounce the switch, and use the Q output to control the CD4053 analog switch position. I'm guessing you are trying to switch an analog signal.

    Check out the datasheet, or the following link. It's geared towards guitar effects, but I think this will get you on the right track.

    http://www.geofex.com/article_folders/cd4053/cd4053.htm

    If you want a more thorough explanation, feel free to PM me.


    edit: Also, a schematic of your project may be helpful.
     
    Last edited: Aug 15, 2010
  3. DigitalReaper

    Member

    Aug 7, 2010
    70
    2
    Can't you just use a SPST switch and use the inverted output as the other throw? Admitedly i'm not really familiar with logic gates so I could be wrong, but you could probably just add an inverter to the normal output if I am.
     
  4. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    A much simpler approach, let the capacitor slow the rate of change to something controllable. Less circuitry and just as effective. The bigger the capacitor, the more effective the debounce (and the longer the recovery).

    [​IMG] [​IMG]

    I get the feeling this isn't what you want, but you are going to have to explain a bit better. Perhaps show the problem circuit?

    The idea to use a CMOS mux/demux is a good one. As long as current is low they act like analog switches. Here is a comparison list with datasheets. The 4051/4052/4053 share a common datasheet.

    4016 4PDT
    4051 8PST
    4052 4PDT
    4053 2P3T
    4066 1P4T

    .
     
    Last edited: Aug 15, 2010
  5. count_volta

    Thread Starter Active Member

    Feb 4, 2009
    435
    24
    Hey blueduck577, didn't think I would run into someone from Pitt ECE department here. Are you still there, or did you graduate? I might actually know you. ;) And yea you are right about Prof Levitan.

    I don't need to switch in analog signals. Basically I want the output of one TTL chip when the switch is open and the output of another TTL when its closed. Any 2:1 mux will work, but I thought there was an easier way. As it is, I have a ton of chips in my design, and I will need to solder them all on and connect them.

    Oh well. As long as it works. Thanks, mux is perfect.

    I will also try the capacitor switch that Bill suggested for the debounced SPST switches I need.
     
    Last edited: Aug 15, 2010
  6. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,535
    The Mux/Demux chips are fundamentally digital, but by making them conductive paths instead of pure digital gates they can do both functions (multiplex and demultiplex). You can buy chips that are purely Mux or Demux, but they aren't as flexible.

    I would highly recommend adding these chips to your repertoire.
     
  7. Marshie

    New Member

    Mar 13, 2012
    1
    0
    Well done Bill_Marsden. I have been trying to find/create a de-bounce cct for a while now. I have a good working 555 system, but that uses a bag full of devices and takes up space. Your three thingie cct has saved the day. I am thinking of etching "Bill" on the board somewhere. Big up's, Ta. :):):):):)
     
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