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Questions tagged [logic-gates]

Symbolic representation of ideal devices implementing boolean functions

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37 views

Logic-based light system

I need to develop a system that turns on the red light when all three switches are off, and turns on the orange light when any two out of three switches are off. The red light part is already sorted ...
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3answers
27 views

Low voltage form a NAND logic gate then the state is high

I've been trying to learn how to use logic gates. I wanted to use logic gate to bump digital signal from 3.3V MCU to a 5V. I took a T74LS38D1 and mocked the solution using two switches connected to 3....
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1answer
55 views

Pull-down resistors on logic gate and decoder inputs?

I'm designing a very basic circuit for testing a switch sequence. I'm using a CMOS decoder CD4028B (link to datasheet) and XOR gate (CD74HC86E - link to datasheet). Reading the switch sequence is ...
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1answer
45 views

Reimplement circuit using 1 2x4 decoder and 2 logic gates

I am a Computer Science undergraduate taking a module on Computer Organisation. There is this typical circuit design question that always appear in my assignment and I'm not sure what is the standard ...
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1answer
49 views

XOR complement simplification

What is (A⊕B)' simplification? i know that : > (A⊕B)=A'B+AB' but what is the complement of that expression?
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2answers
107 views

Implementing a function using decoder, encoder and some gates

Implement the function F(A,B,C,D,E) = A’B’C’DE’+ABCD’E using only the components required from the ones given below: One 3:8 decoder with active high outputs and an active high enable input One 8:3 ...
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4answers
168 views

Replacing a diode-OR gate by a circuit that behaves the same way (also in the presence of feedback loops) without accumulating voltage loss

Consider the following circuit with two OR gates: simulate this circuit – Schematic created using CircuitLab and the Time Simulation: The OR gates with both inputs 0 generate 0, and after ...
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0answers
195 views

Is it possible to build memoryless logic gates? [duplicate]

I would like to build a memoryless (possibly cyclic) logic circuit. Perhaps this is not the best name, so let me illustrate what I would like to have with an example. Consider a state machine with ...
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2answers
993 views

Circuit to Breadboard [duplicate]

I'm currently working on a project which requires me to test the functionality of TTL logic gates by making use of diodes and resistors. To do so I must first place them on the breadboard and then ...
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1answer
36 views

Understanding connection of inputs and outputs of digital circuits - voltage and currents requirements

I looked for resources to find solutions to these kinds of problems online, but I couldn't find them. Please, feel free to recommend resources to study from. This is a homework question. I can't find ...
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1answer
123 views

H-bridge MOSFET NAND gate driver suffered from logic voltage drop

I've tried to reproduce the NAND Schmitt triggers circuit to drive my H-bridge MOSFET as per following source: http://axotron.se/index_en.php?page=34&chapter=0 All my design files are at this ...
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2answers
72 views

how to control power within a triangle automatically

I have two mains powered extract fans with sensor operated controllers. I need to add a third extract fan that will run if either or both of the other two are on. How do I wire this so to prevent ...
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2answers
56 views

Converting this logic condition possible without programming?

I've been busy trying to make a relay print which has 8 inputs of around 6V-24V that powers the relay. However, I want to add a dipswitch which is able reverse the input-relay relation behavior. ...
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2answers
37 views

Indicator light for circuit powered off

The background is Off road motorcycle Radiator fan, temp controlled circuit is powered when key on power is present. User wants a manual switch to kill the circuit...thats easy enough. A Power on ...
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2answers
122 views

Prevent NPN Transistor Base-Emitter Current

I'm making a simple AND gate array out of 2n2222 transistors. Here is one cell: simulate this circuit – Schematic created using CircuitLab When Input "A", is disabled, and "B" is still on: ...
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8answers
8k views

Why are NAND gates used to make AND gates in computers?

Why is this a standard for AND gates when it could be made with two FETs and a resistor instead?
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0answers
44 views

Jellybean Radio Button logic Chip

Below is an LTSpice simulation of a 'radio button' circuilt. Ignore the bottom button, I am working on a 'reset' mechanism to unlatch any of the other buttons. The idea is that the button you push, ...
2
votes
2answers
108 views

Old-school pseudorandom pulse generator (requesting assistance with hardware design)

I would like to design an old-school pseudorandom pulse generator to trigger various types of events (hardware suggestions only please - no programmable ICs). The events that I want to control need to ...
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0answers
58 views

Replacing two corresponding switches as one with logic gates, to supply power, around a DPDT relay

This is one section of a project I'm working on. A user can choose between DPDT functionality (so having "DeviceI" be a motor that goes forward and reverse) or the alternative option to add another ...
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0answers
52 views

Trick/insight to I implement given boolean function with minimum numbers of given gate

I solved bunch of questions which give some function and then ask to implement it with minimum number of gates of specific type, each having specific number inputs. I was making mistakes in all those ...
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1answer
27 views

Finding drain voltage for a resistor loaded CMOS inverter with 0V at input terminal

Introduction: The following example is from the textbook Sedra/Smith Microelectronic Circuits. It is stated in the solution to this example that since both \$Q_n\$ and \$Q_p\$ are both matched and \$|...
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1answer
94 views

I don't understand why this open collector not gate needs diodes

I'm trying to understand why the following circuit, which corresponds to an open collector not gate, needs to use two diodes. The circuit I'm taking about is below: I think I understand the one just ...
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6answers
2k views

Logic: Output a 1 when a = 1 and b = 0

I'm a hobbyist just discovering logic gates and would like to know, is there a logic gate that will only output a 1 when a is a 1 and ...
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1answer
52 views

Can 74HCT buffers work just as well as 74HC buffers between parallel port and target?

I'm making a circuit to program the AT89S52 microcontroller in a serial fashion as follows: Call me paranoid but this time I'm using resistors on all outputs to the micro as well as RC networks on ...
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2answers
45 views

Logic Level Indicator Input Voltage [closed]

Here's a diagram of a logic level indicator and NAND gate. Now I'm supposed to use this in conjunction with some basic logic circuits. However I cannot find out what voltage I should have at the ...
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2answers
96 views

AND gate output when inputs are open

My problem is about AND-gate when its inputs are open. I want to know: What is the output when inputs are open? The output is Z (open) or 0? What is your idea about this AND-gate transistor ...
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5answers
2k views

Help in the closing of a logic circuit

I'm currently studying logic circuits for my exams and came across a question "7. An electrical circuit is set up with four switches. A lamp will light only if the following happens: Switches ...
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2answers
78 views

How do I make a circuit for a push switch that in order to turn on you need to press it 2 times?

Is there any way to make a switch circuit that turn a led on by pressig it two times thank you...
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2answers
117 views

What is the name of this kind of connector where you stick a whole board in to connect?

An example of the connector type I'm looking for a name for can be found on this board: It's the big box. You stick a board in to it with strips of exposed copper to connect. It also seems similar to ...
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1answer
51 views

gates operation in flip flop [closed]

The operation of logic gates in the flip flop is pretty confusing for me. If I am not wrong then the NAND and NOR gates provide output only when there are at least two inputs. But in case of the flip ...
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3answers
127 views

Battery Tester Circuit with 3 LEDS

I'm designing a small system that uses an ATMEGA328P and a LoRa module that runs on 3.3V using a AAA 1.5V battery. The battery is connected to a Boost Converter which steps up the 1.5V to 3.3V to ...
3
votes
3answers
193 views

Latching Soft ON/OFF Button

Would it be reasonable to implement a soft ON/OFF button like this? My design requirements in short: Enable the system power from a single-cell LiPo battery immediately after the ON/OFF button has ...
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2answers
183 views

Edge detection circuit (for rotary encoder)

I managed to decode a rotary encoder using an arduino to read the input signal but I noticed other than the interrupts, the code is mainly made up of lines similar to: "IF this AND that OR that AND ...
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0answers
70 views

Is this logic gate circuit equivalent to the Simulink model?

Is this Simulink model equivalent to this circuit? Although the circuit simulated in Multisim works exactly the same as the Simulink model, switching (S1) between 5v and 0V causes an error. I guess ...
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1answer
94 views

555 circuit problem.. could it be broken?

I've made a circuit that's connected to a 12V+5V power source (attached a gallery. last photo is the schematic) it is simply a 555 timer that goes off whenever one of the two input pins goes high (...
6
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2answers
707 views

Build circuit from a formula

I've this formula: y = AB + AB'C + A'C I've to build a circuit with only a 2:1 mux and a OR port. I've done the truth table and k.map, but i've not idea how proced. EDIT: @jonk Thanks for your ...
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2answers
151 views

Using 3-state buffers for multiplexing

Some while ago, while memorising the 74xx series part numbers, I came across the concept of a device with a "3-state" output. The idea, as best as I can tell, is that the device outputs logic low, ...
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1answer
61 views

How to Design a T filp flop using only basic logic gates [closed]

I know how to design combinational circuits(ex Binary code to bcd code) 1) Draw truth table 2) Draw K - map, derive Boolean funcntion 3) Design circuits from boolean fucntion but I don't know How to ...
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1answer
211 views

Latching Press-on / hold-off toggle switch circuit. Works on breadboard not on PCB

I followed a schematic and mocked up a Latching toggle switch with NAND gates. (see picture below for what I followed) (Source) I have mocked it up onto a breadboard. Using the exact same values of ...
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2answers
84 views

How can I make an OR gate out of two sockets

I have some lights that go into the wall, that I've plugged into this smart outlet so I can control these through my phone. I want to also be able to power them through a movement activated sensor. ...
4
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4answers
190 views

How to ensure an off-before-on transition for an H-bridge?

I want to control a H-bridge using an ATMega2560. The goal is to produce output with +-18V for driving a Merklin H0 digital train set. Given the voltage and current needed for the trains it is ...
0
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0answers
32 views

Transmission gate simulation

When the voltage on node n-mosfet is a Logic 1, the complementary Logic 0 is applied to node active-low n-mosfet, allowing both transistors to conduct and pass the signal at IN to OUT. When the ...
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1answer
53 views

Logic switch using logic gates

I have connected by lithium-ion battery to a tp4056 IC charger with builtin circuit protection(shown below). Which means the circuit will automatically disconnect the load when the battery voltage ...
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3answers
4k views

What is the purpose of an AND gate with the same signal on both inputs?

If this is a buffer, why use an AND gate, aside from better availability of that gate in a single package? This is on an Analog Devices SHARC eval board.
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1answer
39 views

Bias T to level shift output from oscillator

I am using XOR gate HMC851LC3C to get an ultra-short pulse (200ps range). This logic gate requires inputs in the range of -2.5V to 0.5V. However, RF signals from my oscillator is sine wave -1V to 1V. ...
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1answer
54 views

Get Ground when 5V are available

This may sound like a basic task, but I am new to Electrical engineering. I want to combine an QI Charging matt into my SmartHome. When my phone is charged by the mat a Green LED lights up. This LED ...
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1answer
50 views

inverting address decoder with low after high

I have an 74137 address decoder and know how to build one like that from basic gates. But in my use case the address decoder is connected to the enable pins of a number of bus drivers and I fear this ...
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0answers
37 views

“Given a condition, decide which execution should follow” with logic gates

For the system above I need to give 'SR' an input from Hysteresis or Soft-Switching blocks. Whether SR should read one or the other depends entirely on the condition ISB >= 0.5*REF. To visualize it ...
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1answer
145 views

Implementing a Boolean function using NOR gates with maximum 4 ports

I need to implement a Boolean function using NOR gates only. The minimized function written as PoS is: f(a, b, c, d) = (a+b)(a+c+d)(b+c+d')(a+c'+d')(a'+c'+d) I used double negation and DeMorgan's ...
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1answer
78 views

logic gates with 2n222 transistors and leds not working

I am a complete newbie to electronics, But here i go.. I am trying to make some super simple logic gates for now an AND gate. In this logic gate i want to show which out en inputs are high by using a ...