Need assistance clarifying Digital Techniques Studies

Thread Starter


Joined Sep 21, 2010
Hi, my name is Aaron, this is my first time posting on this forum, so let me know if I can improve in any way.

Im new to Electrical and Computer Engineering at the school im attending, and its going decently well, except my Digital Techniques class which im so utterly lost in.
My prof has the WORST notes, the WORST explanations

(Ie he loses himself mid-clarification, and loops back to not answer any questions we ask. The class doesnt even bother anymore)

Anyways, were working right now on Logic Gates, and identifying/discovering pin labels on our 4 switch breadboard... switch.

What im not understanding, is the NC/NO stuff, and producing 1's/0's from different configurations

Is there ANY constant in this course? Anything I can take as a rule and build off of? It seems like we just go willy-nilly and label stuff as NO/NC, 1/0, as we feel like doing it.
I had a lab today that I was hopelessly lost in, and based on the pace this school goes in, im freakin out a little bit

Can someone give me an ACTUAL explanation of the basics of NO/NC works, if you tell me DPDT I can identify what kind of switch it is, but defining NO/NC and its outputs is whats getting me.

Thanks in advance for ANY time in helping me. Fellow student community, HALP!


Joined Dec 5, 2009
An open circuit is a circuit with a break in it. A cut wire.

A closed circuit is a circuit that has no breaks and current is leaving and returning to the power source.

A 'NO' switch is a switch that is Normally Open Circuit Meaning the switch is in the "off" position NORMALLY. When you operate the switch, you would CLOSE it.

A 'NC' switch is Normally Closed Circuit Meaning the switch is in the "on" position NORMALLY. When you operate it, you would break or OPEN the circuit.

When dealing with logic there is either 'TRUE' or 'FALSE'. 1 or 0.

When a logic circuit is described, it is usually shown if it is 5v logic, 3.3v logic, 12v logic (or whatEVER)

SO, if you measured a 5v logic pin and it had 5v on it, it would be 'TRUE' or '1'

So logic uses a voltage as a 'true'(1) and a lack of voltage as a 'false'(0)

Read our e-book for some great, easy to understand info on the subjects.. It just may save your grade.

The WHOLE book starts here:

And welcome. ;)


Joined Feb 5, 2010
Yeah, NC NO. Think of it as BEFORE you put it in a circuit.

When you pick a relay up and look at, before you put it in the circuit, it is NORMALLY in a certain state.

Therefor when the text refers to the NO terminals they would be the ones that are not connected to each other.

The standard view of a relay in a schematic is the Normal state, the un-powered, un-actuated state. It gets confusing because you have to follow a signal to the contact which is NOT connected to the center arm to follow its path when the relay is active. So the schematic shows a set of contacts that touch, but these will not be touching if power is applied to the relay. The ones which are open will be touching so you follow the signal path with that in mind.


Joined Apr 6, 2009
Yup, what they said... When you are looking at a output of zero volts (in a perfect circuit.) the output is said to be low, or "O" . When the output goes high (5 volts in a perfect circuit) it is said to be high."1" Now you have the beginnings of communication. "1001" is a series of pulses that later in your class will be explained as a "binary number" but for now, it is just "high, low,low,high"
NC is just a switch that is normally closed, or "completing the circuit" It offers an unbroken path to ground. Like a drawbridge that is down, allowing traffic(electrons) to flow. A NO (normally open) is a drawbridge that stays up, blocking traffic until you wish to allow it. Hope we helped...


Joined Jul 26, 2010
My prof has the WORST notes, the WORST explanations
I've encountered situations like this in college before and in most cases the chosen textbook for the course sucked. (or the author and I couldn't connect our wording)

Turned out the textbook they were using just a few years before actually made sense so I kept a copy checked out from the library. This has happened in other courses too so I'd hit the library and browse through their selections until I found one that "spoke my language" (so to speak)

Thread Starter


Joined Sep 21, 2010
Hey thanks ALOT guys, that really helped solidify my view on the topic. I was able to do alot of work and study on it and came to the same conclusion all of you just verified.

We were working on outputting 1's and 0's to a test level logic circuit, and that was decently confusing, but I think I got it now.
Just want to say thanks by the way for all of you posting! What a great help this site will be I can tell. Maybe when im confident enough I can repay the favour!

Second question: (and/or should I make a new thread)?

Im having troubles connecting the pins on a schematic to pins on a I/C chip, the 1-9 10-18 (I think) pin layout, and defining what poles are what on a schematic with a SPDT switch for example.

Do you guys know any tricks of any kind to really connect that? Im also going to attempt to find it in the online textbook one poster linked (Thanks!) aswell.

Other than that, were working on OR/AND/NOT gates, and inverses, and bubble logic and stuff and that all seems easy!


Joined Apr 6, 2009
If I understand the question correctly, you are looking to clarify the pins on an IC chip with a schematic. The chip has a notch on one end of it, place the chip so the notch is ar the top, and the pins will start top left at 1, move down to the bottom, switch to the right side bottom and move to the top right. (counter clockwise) . It seems that I read somewhere about a chip that was different, but I believe that is very uncommon. Always consult a pinout datasheet until you are sure. Some chips require pins to be held high/low in order to function properly..