Logic gates(Schematics)

Thread Starter

Zanac-X

Joined Dec 23, 2011
51
for the time being im only going to show it as a sheet to represent "all logic gates" as circuits independent of each other just to figure out "how its made" and "how it runs" then its up to my teammates to really disconnect the inputs and outputs and make a more complex logic circuit with higher efficiency and will be using input signals instead of sources.
 

WBahn

Joined Mar 31, 2012
29,978
But you aren't showing them how it's made or how it runs. Your circuits aren't made and don't run like real logic circuits and they are going to have to pretty much start from scratch to make circuits that can be interfaced together.
 

WBahn

Joined Mar 31, 2012
29,978
then what is your suggestion please
I've already made it. Make circuits that are compatible and can be interfaced together.

One way to do that using the circuits you have would be use an optocoupler.

Another way would be to use relays.

Another way would be to design circuits that take a voltage as an input and output a compatible voltage.
 

panic mode

Joined Oct 10, 2011
2,715
what is the reason you want to use discrete components rather than gates? internal working is irrelevant 99.9% of time anyway, what counts is function (truth table in case of gates). also, the whole point of having gates is to use them to build larger structures (latches, flipflops, multiplexters, counters...). this means you need quite few of them. making each out of discrete components is huge waste of time (you will be building gate circuits, instead of using gates to do appy and learn digital logic). just my $0,02
 

djsfantasi

Joined Apr 11, 2010
9,156
what is the reason you want to use discrete components rather than gates? internal working is irrelevant 99.9% of time anyway, what counts is function (truth table in case of gates). also, the whole point of having gates is to use them to build larger structures (latches, flipflops, multiplexters, counters...). this means you need quite few of them. making each out of discrete components is huge waste of time (you will be building gate circuits, instead of using gates to do appy and learn digital logic). just my $0,02
Because, as the OP stated in his first post, that is his objective. If I am a weekend DIYer and I want to buy a truck, your $0.02 isn't useful. I want a F150, not a Fiesta. Besides, this is for his students, and being introduced to an example of the internals is an excellent objective. I do agree that function is also a necessary ingredient. Many questions here seem to be caused by a lack of or a mis- understanding of truth tables. Then, combining gates can come next.

I re-read your post, and my major trigger in replying was your "huge waste of time" comment. I didn't agree.
 
Last edited:

Brownout

Joined Jan 10, 2012
2,390
i think its done........how about you guys ?
I like how you represented the AND gate. For an abstract illustration of the basic function, I think that is fine. However, for consistancy, I would draw each gate to have the output connected to a transistor emmiter, as your AND gate shows. That way, the same principles of driving the outputs are applied across all the logic funcitons. That requires you to redraw many of the functions.

The inputs should be consistant as well. I didn't look at the inputs close enough to say if they are or not.
 

Thread Starter

Zanac-X

Joined Dec 23, 2011
51
djsfantasi : well thank you i think you just said everything in my mind

the thing is im in a group of students (not a teacher,but it sounded very cool when you said "his students" so thank you for that")and we all decided that every one should find an answer to a problem and at the end of a given time we make a lecture to explain whats going on,as i said before we dont have teacher we just have people that we must call them teachers without any reason that the mind can except.

panic mode :having djsfantasi answered you i just wanted to say thank you for the help without you i could never advance in this topic

another thing to add here is that with the simulation of the circuits i can show the dynamics of current and voltage,and chosen the gates because :

1- its very common in our life

2- no one actually represented them as "the ultimate principle circuit" and we all need to see how things begun,and with this i can show them the huge difference that a human can make if he just begun to think of improving something(and thats the main point that led me to use cells and LEDs as inputs and outputs,as this is the simplest way that a human would start)

3- now comes your point of view in which a simple tiny chip that have four AND gates or NOR gates can really solve all your problems,they are cheep, easy to install and available every where, but we have been using them for so long we just forgot the awesomeness of the chip it self.and with my sheet i will have the ability to let my mates(and in the future "my students") see that its really not just a chip,it a powerful piece of art
 

panic mode

Joined Oct 10, 2011
2,715
don't mind me. i may present my views but they are not binding by any means, you can do as you please. besides, being hands-on is great way to gain knowledge.

my main issues with sample circuits remains interface and quantity (even simple digital elements require quite few gates). about the interface - the AND circuit may look simple and clean but it has a problem - it will work as drawn, but only for very few gates, it cannot be cascaded indefinitely. problem is that output of each gate is always lower than inputs. and if each gate drops signal, you don't get far.
you can take a look at datasheets of TTL chips to see internal circuits (and they are still quite simple).

the actual circuit inside the gate rarely matters and has been different for different technologies (pneumatic/hydraulic, relays, vacuum tubes, N-Mos, CMOS, RTL, DTL, TTL, ECL) and it will continue to change as different technologies are introduced. i looked at TTL, N-MOS and CMOS gates and had to do some sizing. what it boils down to is function and propagation delay. i would not want to look at DIY FPGA equivalent (even single LU).

i think it is more interesting to ask students to build something using specific type of gate. for example make everything on your chart using NAND or NOR gates only. common elements include multiplexers, lookup tables, programmable counters, etc. then you can make own computer system. but this will take quite a few gates (not just one of each).
 

WBahn

Joined Mar 31, 2012
29,978
3- now comes your point of view in which a simple tiny chip that have four AND gates or NOR gates can really solve all your problems.
Given only a bunch of AND gates, you can't solve any digital problem. Given a pile of NOR gates, you can. Similarly, you can with a pile of NAND gates. You cannot with AND, XOR, or XNOR gates.

You CAN do it with what I call IMP and NIMP gates. An IMP gate is an "implication" gate that has the following truth table:

A IMP B => A implies B
A|B|Y
L|L|H
L|H|H
H|L|L
H|H|H

A NIMP gate -- like a NAND, NOR, XNOR relative to an AND, OR, XOR -- is a gate that has the opposite output of an IMP gate.
 
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