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Homework Help: Circuit designs

  1. Dec 10, 2005 #1
    hello everybody,

    my teacher:mad: wanted me to design a few circuits like these;

    1) an electronic termometer,
    2) a circuit that switches on the lights and pulls the pitches in evenings

    by using circuit elements like LDR and NTC.

    pls help me

  2. jcsd
  3. Dec 10, 2005 #2


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    Help us, help you!

    What level are you working at?
    What is a "LDR" and a "NTC" I am relatively familiar with control electronics, but am not familiar with these acronyms, others might be in the same boat.

    What is "pulls the pitches in evenings"?
  4. Dec 10, 2005 #3


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    Probably the "pitches" are the window blinds or something similar. But I'm in the same boat as Integral on the LDR and NTC acronyms. So, a little time at acronymfinder.com.....

    -- Light Detect Resistor
    -- Laser Designator Ranger
    -- Labor-Delivery-Recovery (room) -- yeah, that's probably it with the thermometer part.... :rolleyes:

    -- Negative Temperature Coefficient
    -- Nepal Telecommunication Corporation
    -- NASA Teleconferencing Center -- that's the parts about switching on the lights, I think... :rolleyes:
  5. Dec 10, 2005 #4


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    Hi Common,
    Welcome to the Physics Forums.. you pose some interesting questions.
    Just to give you a little head's up, if this is a homework question we have a section Homework>Engineering
    where you can post those kinds of questions.

    On homework and general questions, there are many of us willing to help, as long as you show us your thoughts first. (see #1 on ref)

    As others have indicated, a good place to start is to tell us what LDR and NTC refer too. What are they? How do they function?
    What grade level is this for? (that will help us gauge at what level to respond). Please feel welcome to the PF forums :smile:
  6. Dec 12, 2005 #5
    ok everybody,
    firstly I apologize to you because of my english, which is not very well.:frown:

    LDR is the acronym of "light dependent resistor",
    and NTC is "negative temperature coefficient".
    berkeman was right.

    but i couldn't understand the meaning of "what level" .
  7. Dec 12, 2005 #6


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    By "what level", Integral was trying to figure out how to tailor his help to the level that you are studying in school. Like, if you are in the US equivalent of high school (15-18 years old), then the answer will be fairly simple. If you are in a graduate year of college, then the answer will be more sophisticated (with temperature calibrations, microcontrollers, maybe some CE-Mark considerations, etc.).

    It sounds like maybe you are in your first electronics class in college, right? What kind of building blocks are you folks using in your class right now? Transistors, opamps, microcontrollers, etc.? What textbook are you using? What Internet circuit design resources has your instructor pointed you toward so far?
  8. Dec 12, 2005 #7


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    common, you are asking us to do your work for you. We will not do this. FOr us to help you, you need to show that you are at least trying to help yourself. You need to give us more background on what you know and "what level" youre at. Show us what ideas/schematics you have come up with. We cannot reach into your mind.

    Like was mentioned before:

    Help us, help you!

    Edit: looks like berkeman got to that first.
  9. Dec 12, 2005 #8
    ok guys,

    i solved my problem. i had needed a dumb circuit, which has one transistor and a few resistors and diodes etc.

    but you were right, i hadn't give you enough data about my problem. forgive me, i'm new at electronics.

    thanks for your interest...
  10. Dec 13, 2005 #9


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    Great job common,
    But now you have me curious, what do your final circuits look like?
  11. Dec 13, 2005 #10
    a dumb switching-circuit

    thank you Ouabache,
    if you're curious really, i'm sending my designs. but these aren't professional jobs, namely don't worth seeing.

    i will simply tell about how that circuit works:
    LDR is "light dependent resistor", when the light coming onto it increases , ldr's resistance will decrease. or vice versa.

    in usual, LDR's resistance is very low(300ohm) and behaves like a short-circuit. because of this, base-current of the transistor is approximately zero and transistor is cutoff.
    in the evening, (sun downs and light decreases) our LDR's resistance will increase(a few Megaohms) and the current will flow above the transistor by force. thus the lights will be turned on and the motor will run and draw the curtains.

    Attached Files:

  12. Dec 14, 2005 #11


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    Thanks for sharing common!! :smile:
    In your left diagram, I wonder what is the purpose using several diodes in parallel, with different values of resistance in series with each?

    Did you happen to construct a circuit using the NTC (negative temperature coefficient) thermistor? If you are still thinking about that, this ref may give you some ideas.:rolleyes:
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