Digital switch with ROM ??

Discussion in 'The Projects Forum' started by DC_Kid, Jun 8, 2009.

  1. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    anyone know of a digital switcher that has power on/off persistence? for my project using rotary dip switches is proving too costly. i need a way to either switch 14Vdc (SPST with 6 positions). it could also just be a IC that takes one of 6 outputs high or low with the push of a button, and with each successive button push the output moves one position, etc. the catch is i need the current selection to stay persistent during power on/off cycles.
     
  2. balisong

    Member

    Feb 26, 2008
    27
    0
    From another thread, my understanding is you need 16 switches x 5 position = 80 outputs.

    Try this on for size:
    16 RA trimpots ($0.20ea)
    2 8-channel analog MUX ($0.50ea)
    Your favorite MCU with ADC ($5.00?)
    1 16-byte serial EEPROM ($0.20)
    1 5V regulator (<$1)
    a few shift registers ($0.15ea) depends on how many IO the MCU is short
    80 NFETs ($0.05ea)
    a few decoupling caps
    a crystal
    a few resistors

    Under $20 in parts.

    Fast, cheap or easy: pick two.
     
  3. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    cheap it is. cheap on board space it is not.

    and not really 80 outputs all at once. my design is modular. a backplane that consists of some common items such as I/O, power supply and filtering, etc. each module is a card-edge pcb and each module needs a user selector input (switch) as "off,1,2,3,4,5" or just "1,2,3,4,5". its a sutomotive application so i need zero probability that the switch position changes by itself, hence a small rotary dip switch would be ideal.
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    To do it without any costs, you can use solder jumpers.
    Draw a line on the PCB and the number of "contacts" you need.
    With a blob of solder you can connect the line with one of the "contacts".

    [​IMG]


    Greetings,
    Bertus
     
  5. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    are you being funny?

    it wont work, this is a user selectable input. the end user has to be able to choose what setting s/he wants, and then change it if need be, etc.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Have you considered DIP headers with jumpers, like the type used on hard drives? Quite inexpensive, available in right angle. Not as convenient as a rotary switch, and it's possible for the end-user to lose a jumper - but easy enough to get replacements.
     
  7. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    header jumper is considered, but not very user friendly for my application.

    what about a non-volatile counter of some sort. instead of counter output being binary its just 1 of 6, this way i could provide a micro momentary push button switch for the user to press? a non-volatile solid state relay IC would be good. would IC's like this exist?
     
  8. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Those kinds of things have been replaced by microcontrollers.

    Why don't you just use a uC with a menu-driven LCD interface? You could have the outputs of the uC drive MUX/DEMUX IC's.

    Your requirement for 5 or 6 positions is rather inconvenient.
     
  9. Propaganda

    Member

    Jun 3, 2009
    22
    1
    Please explain the human input part more deeply...

    How often will the input select be used? How/Where will it be located? Does it need to be accessed quickly for mission critical applications? Are there aesthetic considerations? How much board/control panel space do you have? What is your budget allocation for this aspect of the project?




    So, a rotary dip switch works but is too costly?

    here is something fun.......


    "You were right, someone blew out the hatch. They were all sucked out into space."
    "Correction, sir. That's, 'Blown out'."
    "Thank you, Data."
    "A common mistake, sir." -- Riker and Data in ST:TNG "The Naked Now"






    EDIT*******

    How much amperage? Just one circuit active at one time... if two or more active even briefly will there be smoke?

    6P2T slide switch for $1.47! http://mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMtHXLepoqNyVQ9Lclc%2fSnL8PORU9Cuha%2fE%3d
     
    Last edited: Jun 10, 2009
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
  11. DC_Kid

    Thread Starter Distinguished Member

    Feb 25, 2008
    638
    9
    to answer some questions:

    1. i dont yet have a enclosure selected, but i am trying to get some design ideas before going to the drawing board, etc. the smaller the better. i am currently in the process of building my own SMT oven which has set temp with up and down slope control. i need to step into SMT to reduce the size of my enclosure. what i talk about is just one of 16 modules that go into my enclosure. the enclosure needs to be small to fit under the vehicle hood.
    2. the human interface is a rotary dip or a micro push button (paper clip through hole, etc) with 5 micro LED's. the LED's represent 1 of 5 operations modes, the 6 position would be off.
    3. how often used cannot be determined because the application deals with automotive fuel injectors. the end user might change operational modes from time to time. i estimate though changes not made to often.
    4. yes, just one output at any given time. current is very low, will drive one LED and a fet gate, thats it, so maybe 10mA. i can probably get the LED to light at 5mA.

    solution needs to be non-volatile.
     
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