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# Questions tagged [logic-gates]

Symbolic representation of ideal devices implementing boolean functions

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### XOR in domino logic

I was reading about domino logic and I noticed that several resources mention that domino logic can't be used for inverting functions like (NAND, NOR) and also can't be used for XOR. I understand why ...
32k views

### How can I design a 4-to-16 decoder using two 3-to-8 decoders and 16 two-input AND gates?

I have an idea of how to get started, but not sure where to go from there. Since I am using two 3-8 decoders to develop a 4-to-16 decoder, I want to use 4 inputs out of the two 3-8 decoders. So I'll ...
9k views

### What would be the output of A = 0100 and B = 0111 with S = 1 in a 4-bit binary adder-subtractor?

I understand S = 1 means subtraction and S = 0 means addition. So then, the output would be the result of 0100 - 0111. But since it's negative, I'm not sure how it would be represented. I know the ...
1 vote
1k views

### Transition state between 0 and 1 in logic gates

Logic gates in electronics circuit works by converting analog signal into binary,say 0-3 V.Then accordingly at 0 volts the circuit correspond to low (0) similarly at 3V it correspondent to High. My ...
1 vote
549 views

### static Hazard and challenging questions

i read some notes that wrote: for following Function F, has static Hazard, if B=C=D=1, and for each change in value of A, the Static Hazard 1 can be. Why this statement is True?
4k views

### NOR circuit with two switches

I need to make a circuit that results in a 0(off) when one or both switches are closed. I am pretty sure this is a NOR circuit, but I am confused on how to make it assert a 0 when the switch(es) are ...
530 views

### Can someone check over my schematic?

This is the first schematic I have made that was not a simple LED. I want to know if it seems good before I go and build it (and buy the parts). Here is the schematic: Here are a few of my concerns: ...
1 vote
1k views

### Implementing logic functions using universal gates

As NAND and NOR gates are universal gates, there are often questions like: Make the output $f = (a + b')(cd + e)$ using NAND gates. The problem I face is that I take a long time to first convert ...
1 vote
725 views

### Why do electromechanical relay computers tend to use higher voltages?

So I am contemplating building a relay computer. And I have not seen any information on why one would select one voltage over another. It seems that it would be ideal to use 5V relays as that is ...
2k views

### What is the inverted output for on a D flip flop?

I was asked to find the answer for this, it is a pretty vague question: On a D Flip Flop, what is the Q' output? Look this up and write your answer in your pre-lab report. I am trying to understand ...
2k views

### Link between Combinational Logic and Sequential Logic

I always thought that combinational logic circuits could only solve problems that didn't require memory, but then something struck me. Whenever we are modelling a binary adder with a Finite State ...
355 views

### Simplifying Circuits

I have a question regarding simplifying a circuit of a function below that has 5 logic gates in original. f = (A + B) * (C + D) + (A + B) * (C + D)' + C = (A + B) * ((C + D) + (C + D)') + C = (A + ...
6k views

### Breadboard 7408 2 input AND gate always supplying current, regardless of input

I am currently trying to wire the logic for my dual 7-segment display. I am stuck at my AND gate, and having tried an OR gate as well I have been unable to find why, regardless of input, the output ...
2k views

### Feedback loops and Logic Gates

Setup: a simple 3 bit incrementer that is both connected to a digital display and to itself simulate this circuit – Schematic created using CircuitLab Assuming that there is no clock to ...
4k views

### Problem with making 1 bit RAM memory using transistors

I'm trying to make 1 bit RAM using four transistors (2 NOR gates). I built two copies of the following circuit: I connected a LED to the output "F". Also, I connected another LED to the ...
854 views

### Alternating ON and OFF with logic gates in a simulator

My intent is to make sure that when the top mosfet is on the bottom mosfet is off and vice versa. I'm really not sure that this accomplishes the goal. Is there some better way than this? I'm using two ...
20k views

### Create a CMOS circuit from a logic function [duplicate]

I have to create a CMOS circuit from the logic function: F= ~A + B (notA or B). I made the truth table but I'm stuck here trying to make the CMOS circuit. Any ideas anyone? Thanks! I know it's the ...
925 views

### what is the meaning of the star on inverter gate?

there is an star sign on the inverter gate in my homework circuit. what is the meaning of it? what is the difference between it and a normal one?
2k views

### Can you use a single Bipolar Transistor as an AND gate?

I have recently began electronics as a hobby, and I am curious about the use of Bipolar Transistors in AND gates. Simply put, if I was to use the collector and base as inputs, and run small (~1 volt) ...
1 vote
926 views

### What am I doing wrong? Logisim problem

I'm doing my homework for digital logic in logisim. I need to make function solver for this function: f(x,y) = 6*y-8+x in 4bit arithmetic. Here is my solution but it is not working for some inputs. I ...
323 views

### Simple digital circuit schematic question

Below you'll find the schematic for a circuit I have to build and analyze tomorrow for a lab. simulate this circuit – Schematic created using CircuitLab (Note that the blocks I've shown ...
1k views

### Implementing logic gates in CMOS

I'm trying to build the below function with CMOS, is my implementation correct? $$F = ABC + (\overline{B+C})D$$ I am having trouble with the $$(\overline{B+C})$$ in all of the examples I've seen ...
109 views

### How to get a simplified circuit out of three smaller circuits?

I completed the three basic tasks in three independent circuits; however, the optional part is a bit confusing for me; how could I simplify them in one single circuit? Should I find inspiration in the ...
2k views

### Creating a basic ab + a'c circuit on a breadboard, how are the inputs placed?

I am supposed to design my first circuit on a breadboard and the output will be defined by the logical formula: ab + a'c The problem is I don't understand how are the inputs placed, a b c as inputs ...
152 views

### Best way to OR two LED signals

I am recreating the Adafruit Powerboost 500c Circuit, but I want to reduce the LED's I need down to one. It has four LED's to represent the following signals, next to which I put the desired behavior ...
508 views

### Can I use 1 resistor for both inputs of an RTL NOR gate?

I am working out the ideal RTL NOR circuit to use as universal gates for a large project. Based on what I've found on Wikipedia, to implement a NOR gate using BJTs and resistors, we have the following:...
1k views

### A circuit having 2 inputs and 2 outputs

I am going to design a circuit that should have 2 inputs and 2 outputs. when both inputs are low both outputs should be low when input 1 is high and input 2 is low, output 1 should be a square wave ...
3k views

### Only Allow One LED To Light Up

I'm trying to design a simple circuit for a 4 LED indicator. Its basically like a game show device that has four buttons. The first one to press their button would have their LED light up and "lock" ...
266 views

### Design of a basic half-adder

I know that a half-adder is a combination of the gates: XOR, AND. But how are they combined? And can you give a example and explain which one is the XOR and which one is the AND.
1 vote
320 views

### Which OR Gate to use

I am creating a circuit that will light an LED when either signal A or signal B is high. I know of three choices to accomplish this: a diode based OR Gate, a transistor based OR Gate, or an OR gate IC ...
5k views

### Why are NAND flash and NOR flash named using the terms NAND and NOR?

Is the naming of the two flash architectures related to differences between the two types of logic gates? If so, how? Why does or doesn't this difference also apply to different DRAM or SRAM ...
1k views

### Uses for gate expressions, Nor and Xor

I'm not generally confused by Electronic Engineering, but Nor and Xor are the Gate expressions that like to break that Rule. I can't find proper answers to this question, as they are either: Too ...
826 views

### Reset the raspberry pi with a relay

I'm going to use my Rasp as a GPS tracking and it should be running even if the car is off; however, I don't want run out the car battery. To make it happens I added a battery controller (https://www....
369 views

### Two different 3-AND gates: correct implementation?

One of the questions in my textbook (Introduction to Computing Systems) asks to design a 3-input AND gate. The given solution is as follows: simulate this circuit – Schematic created using ...
4k views

### CMOS OR gate using 4 Transistors

Can an OR gate be implemented using 4 CMOS transistors? The circuit would have two n-type transistors in parallel in the pull-up network, and two p-type transistors in series for the pull-down network....
1 vote
905 views

### JK Flipflop design for conveyor project

I have a small project/problem I am working on. While running a conveyor belt continuously with items on it, I need to stamp every other item. I am using a photocell to detect if an item is present. ...
3k views

### Transistor Based NOT Gate Not Working?

I Followed The Following Circuit For The Logic NOT Gate from This Website http://www.northdownfarm.co.uk/rory/tim/basiclogic.htm Here is My Circuit Which is Intended to Perform The NOT Function and ...
3k views

### problem regarding AND gate using diode

I am currently having problem understanding the basic circuitry of AND gate using diodes and how it works. As we know, the basic AND gate circuitry using two diodes is something like this. And we ...
354 views

### Building a 2-bit adder with a propagation delay of at most 2 gates

An XOR-gate itself counts as 2 gates, so if I use an XOR-gate the delay would already be 2. I have no idea how to do this, as a full adder for one bit already contains 2 XOR-gates (or 1 XOR-gate, 1 ...
852 views

### How to design and implement a sequence detector

I have to implement a Moore machine that has an input L and an output Z. The input line L provides values of 1 and ...
551 views

### What does "realize SoP function using gates with arbitrary number of inputs" mean?

I am confused what "gates with arbitrary number of inputs" mean. If we are asked to realize function SoP(0,2,3,6) using standard truth table using gates with arbitrary number of inputs... how is it ...
248 views

### The "AND" gate function

I am learning about the "AND" gate function in Navy school. What I know is that when a low voltage is at the base of Q1, the transistor is in cutoff mode since the collector is reading high (> 2 volts)...
3k views

### Design a 4-bit PISO shift register with 4 DFFs and 3 AND gates

I want to design a 4-bit PISO shift register with 4 DFFs and 3 AND gates. I have gone so far that these two designs can be implemented, but I can't go further minimizing it so as to use 3 AND gates ...
4k views

### Difference between an inverter and a buffer with active low input

In logic diagrams found in datasheets (e.g. Texas Instruments 74HC316) I've often seen both inverters and buffers with active-low inputs ("negated buffers" or "inverting buffers" or whatever they are ...
1 vote
1k views

I am trying to make an asynchronous adder that holds three bits and adds two to the number. Can someone help? A Google search shows nothing and I'm having a hard time visualizing how to make the ...
3k views

### Of what use can a logic gate be to a circuit that contains a micro-controller

I am wondering if a logic gate would be of use to a circuit that contains a micro-controller.Are there cases when an analog logic gate is preferred over a micro-controller and what are some of the ...
192 views

### Are there any single logic gates which are just individual components?

As the question says, I need a NOT gate for a simple Bi-Colour LED circuit. I do not want to use an IC with 6 or 7 integrated as I am only going to use 1, so it's just a waste. So, do individual ...
1 vote
2k views

### NAND gate that outputs 0 when all inputs are 0

I'm trying to work out a piece of binary logic and this is essentially what I am trying to achieve: ...