Trying to create VVR, running into planning issues

Discussion in 'The Projects Forum' started by Joekuh, Jun 11, 2013.

  1. Joekuh

    Thread Starter New Member

    Jul 17, 2012
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    Ok, here's my issue. I have a 4V input, and multiple outputs: 0V, 1V, 2V, and 3V. I have a switch that, when pressed, will control the outputs. What I need is some type of device that can "read" the different voltages that come through it when I press a button on the switch, and activate the appropriate action. Is there something out there that can do that? I'm not a n00b at wiring, but this is something completely different from anything I've ever done before. Any help will be greatly appreciated.

    [​IMG]
     
    Last edited: Jun 11, 2013
  2. wayneh

    Expert

    Sep 9, 2010
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    So you want it to toggle from one voltage to the next each time you press the button?

    How precisely do you need to control the voltage, and is your input really fixed at 4.0V? How much current do you need at each voltage?

    Oh wait, you already have the voltages, you now need a way to "translate" them? You may be able to use an LM3914 which is designed to discriminate voltages. An alternative would be to make your own window comparators around each voltage, for instance 3.0±0.2V.
     
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  3. Joekuh

    Thread Starter New Member

    Jul 17, 2012
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    I bolded the exact issue I was banging my head against. Window comparators is an EXCELLENT idea. Thank you for taking the time to translate my poor explanation of what I'm trying to do :( .
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Haha, well it took me a minute and couple wrong turns but I got there.
     
  5. Joekuh

    Thread Starter New Member

    Jul 17, 2012
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    Further searches have helped me stumble onto this solid step towards a solution:

    [​IMG]

    (Full credit to http://munro.humber.ca/~lloyd/ceng306/WindowComparator.pdf for originally drawing up this schematic.)



    What I'm trying to do is different, obviously. My idea is to set up window comparators for 0,1,2, and 3 volts versus a 4 volt reference voltage. If i use the same schematic, I wont achieve my desired result. For example, if I press the 2 volt button on the switch, the 0,1, AND 2 volt sequences will be initiated; That's how I think it would work right now. How do I edit my schematic to reflect a result of only the 2 volt output being triggered when I press the 2 volt button in this circuit? I'm not asking someone to reinvent the wheel here for me, just please point me in the right direction, and I'd be happy to work on this until I figure this out.







    At least until the next unexplained question pops up.
     
  6. wayneh

    Expert

    Sep 9, 2010
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    The LM3914 or LM3915 (one is linear, one log) can be set to operate in either bar mode or dot mode. I believe you are describing dot mode, where only one LED is lit for a given voltage range, not the ones below it. The schematic you linked does not show window comparators, but a bargraph style using simple comparators. I can't imagine how you'd do a dot mode that way. Maybe there's some trick I don't see.
     
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