1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to make a Logic Circuit with 5 LEDs and a 3V battery? Nothing else allow

  1. Jan 14, 2013 #1
    1. The problem statement, all variables and given/known data

    We can't use anything else, and just have to make a logic circuit (either OR, AND or NOT) with just this material. We can use less or more diodes but I have only 5.

    2. Relevant equations



    3. The attempt at a solution
    I tried setting it up like doides but no help at all. I thought LEDs would function same as diodes but it didn't.
     
  2. jcsd
  3. Jan 14, 2013 #2

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    What logic levels did you use?
     
  4. Jan 14, 2013 #3
    I just need a simple level 1 logic. Like simple AND or OR.
    And I can't use that switch equivelent.
     
  5. Jan 14, 2013 #4

    vk6kro

    User Avatar
    Science Advisor

    If you were asked to make a 2 input OR gate, could you make one with 2 diodes and a LED?

    You can specify which colour LEDs you are going to use.
     
  6. Jan 14, 2013 #5

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    I meant what voltages :-)

    Have a look at the I/V curve of various LEDs and compare with diodes.
     
  7. Jan 14, 2013 #6

    vk6kro

    User Avatar
    Science Advisor

    The question specifies a 3 volt battery, but two RED LEDs can run in series off a 3 volt battery. One could function as a diode and the other as a LED showing the output state.

    Remember the truth table for an OR gate.
     
  8. Jan 15, 2013 #7

    CWatters

    User Avatar
    Science Advisor
    Homework Helper

    Anything to stop you defining a logic 1 as a 10mA current rather than a voltage :-)
     
  9. Jan 15, 2013 #8

    collinsmark

    User Avatar
    Homework Helper
    Gold Member

    If the assignment is flexible regarding the current capability on the input signal(s), then I suggest researching a little about "open-collector" gates, as a starting point.

    Normally, we're accustomed to logic gates having voltage rails that are separate from the inputs and outputs; and normally inputs have very high input impedance, and outputs have low impedance. But you might want to ignore that for this exercise. If impedance/current requirements are laxed, than this is separation is not always necessary.

    As a matter of fact, it is possible to build at least one of your logic gates with a single LED*, using this open-collector [like] scheme. (Following the same idea with the emitter will create yet a different type of gate.) You may not be able to build all types of logic gates with just LEDs alone, but you can build at least a couple of them.

    *(If the output state is indicated by the LED lighting up or not)

    I'll let you figure out how many types can be built.

    [Edit: It also can make a big difference depending on what your inputs representations are. For example, if input state '1' is represented by Vcc; and input '0' by "no-connection" allows for different opportunities than '1' being Vcc and '0' being GND (0 V).]
     
    Last edited: Jan 15, 2013
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: How to make a Logic Circuit with 5 LEDs and a 3V battery? Nothing else allow
  1. LED Circuit Design (Replies: 13)

Loading...