# Questions tagged [logic-gates]

Symbolic representation of ideal devices implementing boolean functions

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1answer
41 views

### Connect outer the Gates (AND ,OR)

I have the equation L=ABD+(A+B)(D+C). I have this I must connect those based on the equation. What I did was to take the equation ...
1answer
40 views

### Gates output waveform

I want to do the waveform of X output. How can I do this? I am trying to use Tinkercad. There is an oscilloscope so I can see the palm. I couldn't get Tinkercad to represent the palm. It doesn't have ...
1answer
58 views

### 3 Bit Counter w/ 7 Segment Display Starts at 111 instead of 000

The goal for this task is to have a 7 segment display output my last name the first two initials of my first name. The output should be FURMANHE with F being the 000 state and 111 being the E state. ...
2answers
88 views

### VHDL — K-map reduced characteristic equation fails

I have this circuit (D-latch): and I can directly write the logical equation by only watching the gates: $$Q = \overline{(\overline{(D \cdot C) + Q}) + (C \cdot \overline{D})}$$ If I want to ...
2answers
54 views

### For multiplexers, what are the pros and cons of Three-State Buffers vs “Straight Gates”?

This came up from my previous question when looking more closely at multiplexers. Wikipedia article shows two ways of implementing them. One with some Three-State Buffers, and the other that's just &...
2answers
84 views

### Why pull down and pull up resistors are necessary?

I just started building some logic circuits for gaining some experience in the summer while waiting for the next semester and I learnt about the concept of pull-up and pull-down resistors. The concept ...
6answers
895 views

### Difference between no input and a zero input in digital electronics

I'm new to digital electronics and try to understand how logic gates works. In books many times Zeroes​ and ones are referred as Low and High respectively, is Low and High used as an indication of ...
0answers
21 views

### How would you build a DEC to BCD encoder with 10 bits?

Yeah, so I was looking at some school lectures and there we had a 4 bit encoder and decoder. That's easy, small and wouldn't take much time to build. You can achieve number 0-9 with only those four ...
6answers
2k views

### Why do CMOS NOT gate designs differ from BJT NOT gate designs?

If you look for an inverter circuit on Google Images, you'll find something that looks like this: This inverter design has a single NPN transistor. However, on Wikipedia's article about transistor ...
0answers
41 views

### Is it possible to draw Programmable-Array-Logic (PAL) circuit with empty lines?

Can I draw PAL circuit to execute the function $f = abc + d$ by using 8 inputs and 3 AND gates? I did it like this:
2answers
63 views

### Exponential Circuit [closed]

I want to amplify a voltage by x to the power of x/4. So, basically, if I have 9 milivolts, I want it to amplify to 92.25 milivolts. Simple enough in theory, but I've so far found no actual way to do ...
0answers
47 views

### How to change flip-flop type using multiplexer

The idea is to create a D or T flip-flop from a JK flip-flop and a 2-entry multiplexer. If the selection line is 0, the flip flop should act as type D, and if it's 1 it should act as a type T. a NAND ...
1answer
101 views

### Meaning of logic operation “ a' ”

I have found the following expression: c = (a'.b) what does it mean? I know a.b is a and b (...
1answer
41 views

### Noise reduction in ECL logic gates

In this ECL circuit, how he got the equivalent circuit for the noise voltage and what is the meaning of hib4 in the equivalent circuit.
1answer
86 views

### How to calculate overall average propagation delay for digital circuit given

Using the circuit shown with 3 inputs {A,B,C}, and outputs {F1,F2,F3}, and using the average propagation shown below for each gate: AND -> tpd = 9ns, XOR -> tpd = 8ns, OR -> tpd = 10ns ...
3answers
109 views

### Why do we always implement the complementary of the boolean expression when we design a CMOS circuit?

I am new to implementing boolean expressions in CMOS form, and I understand that the "C" in CMOS stands for "Complementary", so it is an inverter circuit. What I don't understand ...
3answers
488 views

### How could I essentially design an if/else statement as a circuit using basic logic gates?

So for my circuit, I have set up a simple game of rock paper scissors. I have the actual gameplay of rock paper scissors working, where it will correctly choose the winner and light up corresponding ...
1answer
44 views

### Is 2:1 Mux (Multiplexer) same as 2:1 Encoder, theoretically?

I just came across a question states: A Combinational circuit which is used when it is desired to send data from 2 or more sources through a single transmission line is known as: ______ I know it is ...
3answers
108 views

### Is a base resistor always needed in a single transistor inverter circuit?

For the circuit shown, I'm trying to figure out if I need a base resistor or not. What I'm looking to accomplish is a simple logic inverter to hold a power amp's active low shutdown at logic low ...
2answers
45 views

### feeding OR gate output to its own input

I'm %100 sure it's been asked before many times, but seriously can't find an answered question here. let's say I have 5 logic outputs from a chip. in order to OR them into a single Hi/Low signal, can ...
2answers
96 views

### GAL 16v8 tri-state independent pin control

I would like to use GAL chips for a project. 16V8, 22V10, 26V12. I have read that the tri-state status of a pin maybe controlled individually. I do not understand how write the equations to ...
4answers
1k views

### Why are the outputs of these gates tied together in the Apollo Guidance Computer?

In looking at the AGC schematics, I'm finding a lot of instances where the outputs of some of the NOR gates are tied together when feeding into another gate. The most dramatic example being here, ...
5answers
3k views

### Why do we put transistors in logic gates? [closed]

I was recently doing some experiments on a breadboard and I decided to try to make a not gate with a single transistor. It worked. Then I tried taking the transistor out of the circuit, connecting ...
5answers
94 views

### A question about propagation delay [closed]

A gate has a propagation delay of 20ns, we know that if we apply a input signal whose duration is less that 20ns , that signal will not change the output state of the gate, similarly, if the duration ...
0answers
24 views

### Combining MUX 4x1 to represent 5 variable function

I have the following function x’y’zw’v’ + x’yz’w’v’ + x’yzw’v’ + xy’z’w’v’ + xy’zw’v I should implement it using only 4x1 MUX (more than one allowed, of course). I'm clueless on how could I combine ...
1answer
80 views

### Calculating propagation delay for a logic circuit

Given the above combinational logic diagram, How to calculate the propagation delay? AND->OR->AND-NOT NOT->AND->NOT I see the above two longest paths. So what I understand is just take ...
2answers
87 views

### Power on state of D Type Flip Flop

I'm looking at the following two d-type flip flops to create a toggle for the EN pin on another IC. I was going to feed Q back into D with an inverter such that it is toggled when clocked ( would this ...
1answer
94 views

### A simple circuit of NOT using a buffer

First of all, I am new to the area of electronics and I want some help to stuff that may sound to you a little obvious. I've seen a circuit using transistor that is used as a NOT logic gate, as in the ...
0answers
25 views

### Not Getting Proper Result From Counters in Proteus Simulation

Circuit Description: This circuit should works as a over counter. Which should count from 0 to 5 then it will give the pulse to the next IC Problem : I found a circuit from online where they build a ...
2answers
74 views

### Magnitude of a binary number with circuit

I'm trying to solve this exercise: Given an 8 bit binary number (if negative it is expressed in two's complement representation) design a circuit that allow to obtain the magnitude of that number. (...
1answer
54 views

### Can two On-Off valves be independently or concurrently switched with my hardware?

I am having a ton of fogginess today thinking of a way to switch a couple On-Off valves with the hardware I'd like to use. When I say 'On-Off', I mean the valves pictured below, where applying voltage ...
2answers
61 views

### 7432 always output 1

So, Im wireding this Edit: Everyone switch ON for good reading And the output is the green leds of each protoboard, 2bits for each protoboard, and with those bits, I have to do a "AND" or &...
0answers
84 views

### How does a two input transistor AND gate work?

I'm trying to self study electronics. I started reading a book on digital electronics and I got stuck on the first chapter. It's about the logic gate circuit. There is a two input AND gate circuit and ...
1answer
57 views

### What is wrong with my 2 bit adder? [closed]

I'm trying to make a 2 bit adder in Logism. I made a half adder and a full adder chained together. Some equations work, and some don't. I'm using the structure that I see everywhere on how to make an ...
1answer
68 views

### How to turn this booth's algorithm state machine into a circuit?

I have a project of a booth's algorithm circuit, but I have problems with properly translating the FSM into a circuit. I've made the following FSM, and I can't turn it into a circuit that dictates the ...
3answers
724 views

### What is the role of the pull-down resistor in a diode-transistor logic (DTL) gate?

What is the function of R3, and what happens if we operate the circuit without it?
1answer
98 views

### Replacing a logic OR gate with two diodes

I am trying to build some basic circuits to figure out how things work (mostly for fun). This one caught me off-guard today. I want to build a module with three pushbuttons. Each one turns its own LED ...
1answer
52 views

### Emulate MUX gate by combinations of XOR, MAJ, or any other

What's the smallest combination of XOR and/or MAJ gates (with inversions (NOT) possible at any point) that has the same truth table as a 3 input multiplexer (2x1 MUX) gate? Which is: ...
2answers
118 views

### CMOS (wrong) OR gate with 4 transistors

I'm currently reading through Introduction to Computing Systems: From Bits & Gates to C & Beyond and I'm a bit confused about the outputs of this OR gate (which is not an OR gate): And here ...
0answers
19 views

### Determining max clock speed using a logic tutor

Data sheets have been provided for all 4 logic gates in the image and I will insert them below as I myself am mostly struggling to understand them due to the majority of information on them. I'm not ...
2answers
73 views

### What is the simplest logic circuit + latch that satisfies this truth table?

This is not a homework problem, I'm just revisiting/relearning the practical applications of latches and logic circuits and I've been trying to figure this out on my own. Basically, I want to turn one ...
1answer
43 views

### I can't get the equation of a karnaugh map

MD\F 0 1 00 0 1 01 0 1 11 1 1 10 0 0 this is a karnaugh map. Now , I take in horizontal 1 1 . As a result I have M*D. The F is 0 if we see that it means NOT F and we have 1 so ...
1answer
58 views

### How does ground affect a circuit with a diode, connected to the power source which is connected to a ground and an LED for it to act like a NOT gate?

I was searching for a way to use diodes to make a NOT gate. I found a circuit online and simulated it in an application. The configuration has a battery (1),where the negative terminal is connected to ...
2answers
62 views

### Questions about signal and logic circuit

I just learned about basic logic and logic circuit from a Discrete Math book and I have a few questions: What exactly is a signal in Engineering? From Wikipedia, a signal is defined as a time-varying ...
0answers
102 views

### I need help finding out how to prevent my components from exploding (TinkerCad)

Basically, I'm making a logic circuit on TinkerCad and I need to turn on a seven-segment display but some of my components explode and I've got no idea how to solve this. The components I'm using are:...
0answers
45 views

### Multiplexer instead of multiple AND gates?

I have to use a standard 74hc595 Shift Register and monitor all of its outputs that I have previously set at my will as 1s and 0s. Because I have certain constrains on the monitor lines that cannot be ...
1answer
108 views

### Paging out ROM after boot up

Building a Z80 computer, would like to boot CP/M from ROM and switch the ROM off after initial boot to make whole 64k RAM available for the CPU. Solution I've got so far is using a flip-flop to ...
0answers
34 views

### How to know whether addition has been done in a parallel binary adder?

I am little new to electronics and getting some high level overview of digital electronics. The question is that how to know whether addition has been performed in a logic circuit. For example I have ...
0answers
56 views

### Arithmetic - Absolute value

I constructed a circuit that calculates the absolute value of a signed 4-bit number in two's complement Then the second question of the exercise was to show the correctness of my circuit using the ...
1answer
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### Troubleshooting 74LS136D in Multisim

Hello. I couldn't seem to get my U1A to work. I understand the open collector logic gates, like 74LS136, require a pull-up resister in its output terminal. An open collector needs to be powered-on. I ...