Just Started My EECE Classes

Discussion in 'Homework Help' started by Ripneumann, Sep 6, 2015.

  1. Ripneumann

    Thread Starter New Member

    Aug 24, 2015
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    I am pursuing degrees in Electrical/Computer Engineering and possibly also computer science and will be using this thread to ask questions about my engineering classes I just started up on. We have started learning the basic logic gates/gate diagram/truth table stuff and have slightly gone into hands on practical use using the Cadet training system. I also have picked up the iCircuit app and encourage anyone who's willing to help me out to post any type of information i will need to know with examples and explanations using iCircuit. I will be willing to try out boolean algebraic equations and do examples you give me as long as they aren't too far out my current experience with EE. We have just got into the NOT OR and Inverter gates and mostly basic equations. I am trying to learn ahead of my class schedule so anything is appreciated.
     
  2. WBahn

    Moderator

    Mar 31, 2012
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    Welcome to AAC and good luck in your classes.

    Instead of expecting people to "post any type of information" you will need, the better approach is to come here when you are having problems understanding something or working through a homework problem. Start a new thread for each different problem and show your best attempt at working it. We can then see what you have done right and what you have done wrong and what your approach seems to be and then we can offer suggestions or ask leading questions to help steer you back onto the right path.
     
    Sparky49 likes this.
  3. Ripneumann

    Thread Starter New Member

    Aug 24, 2015
    12
    0
    Yes I will, but I was just stating that I would be open to anyone who has any suggestions. I haven't had too much trouble with the workload of my class right now. I posted a picture of a circuit i figured out but still would like a better understanding of what is actually going on. Also if anyone can help me get an understanding of ohms law and when i use it that would be appreciated. I haven't looked much into it as my class is now learning binary, decimal, and hexadecimal numbers/conversions which I know. The pace is very slow.
     
    Last edited: Sep 6, 2015
  4. WBahn

    Moderator

    Mar 31, 2012
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    Posting a circuit and asking people to tell you about it usually won't get you much in the way of response. The reason is pretty simple -- we have absolutely no clue regarding what you do and don't understand about the circuit or the level of understanding you have and/or are seeking. It will work a LOT better if you ask some specific questions about the circuit. If you have a circuit that is supposed to do something specific, then you can explain what it is supposed to do, post a circuit that you think will do it, and ask for feedback regarding the circuit.

    For the circuit attached:

    upload_2015-9-6_13-42-1.png

    You don't way whether you want the LED to light up when the switch is open or when the switch is closed, so that makes it hard to provide much commentary.

    Having said that, I can tell you a few ways in which this is a very poor circuit (though many simulators won't call you out on it).

    You don't say what logic family this is for. TTL, CMOS, etc. But, in general, logic inputs should never be left floating. This is critical for CMOS and less so for TTL (which generally has a weak pullup behavior for the inputs). So all of your unconnected A pins (2A through 6A) need to be tied to a stable logic level (either VCC or GND will work in this case). Leave unused outputs unconnected.

    When your switch is closed, pin 1A is tied to Vcc. Fine. But what about when it is open? It will be floating and, hence, undefined. The simulator may treat this condition as a logic LO, but chips in the real world usually won't. TTL chips will treat it as a weakly-asserted HI. CMOS chips will respond erratically and, possibly, catastrophically. This can be easily dealt with by using a moderately high-value resistor between pin 1A and GND. When the switch is open this will act as a "pull down" resistor and make the input see a logic LO. When the switch is closed, the hard connection to Vcc overdrives the resistor and asserts a logic HI.

    Many logic families are able to sink significantly more current than they can source. Your circuit is asking the 1Y output to source about 10 mA of current when it is HI and to sink nothing when it is LO. Many logic families simply can't output that much current, though many of those can sink that much current. So, when possible, connect your LED between Vcc and the output pin (with the resistor, of course) so that it lights up when the output is LO.
     
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