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Questions tagged [digital-logic]

Digital electronics treats discrete signals, unlike analog electronics that treat continuous signals. Digital logic is used to perform arithmetic operations with electric signals, and constitutes the base for building CPUs.

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How do I calculate rise times for a push pull GPIO with load?

simulate this circuit – Schematic created using CircuitLab This is a simplified example of a push pull GPIO found in most microprocessors, with a load attached. Using the capacitance and ...
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2answers
213 views

How to write or generate test cases(or vectors) for automated production testing of embedded electronics?

My question is following: Assuming I have developed some embedded controller(board) which has some tens of digital inputs and outputs. It has embedded firmware, which performs some logical functions. ...
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2answers
73 views

The Pin 1 Problem in Audio, Star and Mesh Ground, and Contradictory Grouding Practices in Audio and Digital Systems

I recently came across the concept of "Pin 1 Problem" known in the pro-audio electronics. It seems straightforward at first, but becomes confusing when it comes to grounding. Let me describe the ...
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1answer
137 views

What effect does a logic analyzer probe have on a circuit?

I have an MCU controlling a LED sign. This sign speaks the HUB75 protocol, which is essentially a large shift register. Being a shift register, this requires a clock signal to be generated, which the ...
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70 views

Bipolar transistors that only connect via base to emitter

I am trying to understand how to use this configuration of the LTC2992 power measure IC and the only part I am confused with so far is the two transistors which I have circled. What I know so far ...
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1answer
65 views

What is the least expensive way to build a three-bit shift register?

I'd like to build a queue of three internal bits as inexpensively as possible. Externally, the queue has two input bits and one output bit. The inputs are (dataIn) and (shift), and the output is (...
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74 views

I’m having trouble solving this digital circuit. Help!

I need to design sequential logic circuit from this state diagram using only 2 D-latches. And this is my attempt: If I put it in the simulator it just gives me error and wont count. I assumed that ...
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233 views
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122 views

How to properly constrain ethernet phy

I am trying to use the ethernet PHY on my Nexys4-DDR. The manual for the phy gives the following timing constraints for the RMII ports. I am getting confused as to what exactly the constraints for ...
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200 views

Digital Comparator from LSB to MSB using Lookahead

This is homework to be upfront, but I'm really stuck on it and just need some kind of direction. I've been assigned to create a 16-bit lookahead comparator going from LSB to MSB using no more than 4-...
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4answers
3k views

How to display 2 digit number in binary adder circuit?

I've made 4 bit adder circuit using 4008 IC. And the sum output of the two 4 bit numbers from that IC was feed to one BCD to 7 segment decoder (74LS47) so that I can get decimal output. But since I ...
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218 views

Two different ways of writing the same thing but generating different behaviours in Verilog

I have a part of Verilog code that is basically trying to synthesize a flip-flop. I have been experimenting and it seems that I can come up with two ways of writing it. The first way being : ...
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202 views

How to add two output expressions to calculate the third expression in Cadence icfb 5?

I am trying to calculate the average propagation time carry_TP from carry_TPHL and carry_TPLH which I already got the expression from the calculator tool and works well. Now how do I make the third ...
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361 views

Digital dice counting from 1 to 6

check it out guys ]3]3 the circuits above are both for an electronic dice that is supposed to count from 1 to 6 but none of the LEDS are turning on for the one that is far below, can anyone tell me ...
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1k views

What is bit-true implementation

What is bit-true implementation (with an example if possible)? I was reading a paper and it was stated "a bit-true implementation of the algorithm on a FPGA was performed." So what exactly is bit-...
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560 views

Which serial protocol or encoding scheme does this scoreboard use?

I am trying to decode a signal stream coming from a Nevco scoreboard controller: Packets like this are sent every ~2.7 ms. I suspect it is some sort of UART signal because it is on the RX line of a ...
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0answers
3k views

Constructing Excess 3 BCD to 7 segment decoder - circuit hints needed

I am currently trying to construct a circut for an Excess 3 BCD to 7 Segment decoder. Therefore the input range ranges from 0011 to 1100 in binary inclusive with the rest of the inputs being don't ...
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1k views

How to compare carry-lookahead and ripple-carry adders?

I am a bit stuck with the concept of carry-lookahead adder so I'd like to compare it with another concept I'm more familiar with: the ripple-carry adder. I'm trying to make some basic math comparison ...
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64 views

How to understand min/max voltage specification in datasheet?

I've seen different types of min/max voltages in this datasheet and not sure whether I've understood them correctly, so I want to double-check it here. As shown below, there two types of min/max ...
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1answer
53 views

Implementing a SN74LS245 Octal Bus Transceivers With 3-State Outputs in Logisim

I'm testing out different circuit simulator programs and I was able to build the integrated circuit SN74LS245 Octal Bus Transceiver in a program called Digital ...
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2answers
102 views

Measuring wow and flutter of a phonographic turntable with digital equipment

Old school way to measure: 3000 or 3150 Khz test tone from test record played back through phono cartridge/preamp into wow/flutter/drift meter and for turntable that has an electronic adjustment to ...
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1answer
147 views

Which of these is the correct circuit for JK flip-flop

Are both of these correct ? I am seeing both of these in different places
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52 views

Reverse engineering LCD signals on HP power supply

I have recently acquired an HP 6632A power supply and was inspired by Roberto Barrios' project of replacing the screen with an OLED display to do the same. However, it is evident that the 6632A is ...
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0answers
64 views

74AHCT244 did not output the required signal. What could be the problem?

I am using an STM32 to control my TLC5940, which uses different voltage levels. The circuit layout is in schematic shown above. I wrote a small program to toggle my ...
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58 views

1.5 bit pipeline ADC

How do we combine bits obtained from different stages of 1.5 bit pipeline ADC. Can it be generalised for k bit pipeline ADC ? each stage has three region - 00 , 01 ,11 in 1.5 bit pipeline adc
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1answer
45 views

Xilinx FIR filter behavior

We're currently simulating some Xilinx AXI Stream Finite Impulse Response (FIR) IP cores. https://www.xilinx.com/support/documentation/ip_documentation/fir_compiler/v7_2/pg149-fir-compiler.pdf The ...
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1answer
22 views

Common output from two proximity sensors

I need help wherein I'm using proximity sensors to trigger an event in a device. The device looks for 12V from the sensors and registers it as an event trigger. There's no problem when I'm using one ...
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34 views

Will this attempt at building a four transistor multiplexer work?

Ordinarily I think most people would build a multiplexer out of a NOT gate, two AND gates, and an OR gate, which would involve seven transistors, wouldn't it? I want to see if I can do a multiplexer ...
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54 views

Voltage Across NMOS and PMOS Transistors

So I have the question above concerning an NMOS and PMOS transistor. The goal is to find V1 and V2 in steady state. My understanding is that because the gate voltages of zero and Vdd are there, the ...
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0answers
64 views

Laser Tag System Design Review

I have been working on a project to make my own laser tag gins and sensor vests. I have completed the electrical side of my design but this is the first time I have designed something like this and ...
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4answers
104 views

Noise margins logic circuits

The noise margin is the difference between the min input HIGH and min output HIGH. What is the significance of it? Lets say the input HIGH voltage is currently 2.8V, a noise spike of -0.5V would still ...
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1answer
56 views

Why input combinations producing output '1' constitute a standard SOP expression and those producing output '0' constitute a standard POS expression?

Why input combinations producing output '1' are picked for forming a standard SOP (Sum of Products) expression and input combinations producing output '0' are picked for forming standard POS (Product ...
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45 views

Implementing a circuit that takes a 3-bit number and multiplies it by 8 using only 1 4-bit adder

I was solving a past exam and this question popped up and nobody seemed to agree on an answer. Someone suggested this solution which is just hacking your way to the required result. That suggested ...
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2answers
660 views

A circuit to convert 4-bit Gray numbers to BCD

I'm sorry for asking this specific question here but can some one please tell me what's wrong with this solution. Question: design a circuit to convert 4bit Gray numbers to BCD I have to say I ...
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1answer
166 views

Unsigned multiplier

So I'm trying to build a 4-bit 2's Complement Multiplier on logisim. Here's what I have so far...The first pic is like an overview/drafting, the little chart on the right is accurate I think. The ...
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58 views

Derivation of stability criterion for type 3 digital PLL

Could anyone help to derive the following expression (4.23) which is the stability criterion for type 3 digital PLL ? Note: Screenshots are taken from Floyd Gardner's book : Phaselock Techniques 3rd ...
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41 views

Problem based on Latches (Sequential Circuits)

I am trying to solve the following question: I want to know: If the truth table for \$ Q_{n+1}\$ and \$\bar Q_{n+1}\$ is correct. I have found out the Reset and \$Q_{n}\$ conditions. However, I see ...
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70 views

Make a double-tapping button (ideally without ICs or keeping ICs to a minimum) for a small “tiny cell” powered device

Conditions: small device, extremely space constrained (large caps are a no-go) Powered by a small battery (something like under 120 mah) Thus, adding a few more ICs like the 555 or "TimeBlox ...
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1answer
86 views

Boolean Algebra Equivalent

I am having a little trouble knowing what theorem to use to solve the following problem. Express the given equation without using OR gates. Hint: the expression two NANDed literals looks like this: (...
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0answers
80 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, ...
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0answers
55 views

How do I get the FSM table from the given diagram?

Given one is question and another solution. I cant come to this solution. can anyone help here
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1answer
126 views

TXB0102 only translating in one direction

First time using the TXB0102 and I can only get it translating in one direction. I'm using it to interface a 5V ATMEGA2560 hardware UART port to a 3.3V device with VOH 2.4-3.1V (TXB0102 table says ...
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2answers
157 views

Bus tapping in Xilinx ISE for 8 bit to 16 bit conversion

I have a processing unit which is controlled by a sequencer/control unit. The agenda of this processing unit is to multiply 2 numbers using 8 BIT registers using the bit shift and add method. Once ...
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0answers
102 views

Can someone please help me with this pipelining question

A pipelined implementation of the circuit shown below is to be designed. The delays of the building blocks are indicated inside circles. You are given buffers with a delay of 0.5 ns, and flip-flops ...
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3answers
278 views

How to 'Shift in Parallel' in a shift register?

I am trying to design a basic calculator that can add, sub, mul and div with Logisim. To store the operands I am going to use shift registers. I have recently learned about them and I understand what ...
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3answers
220 views

Maximum resistor values for transistor inverter (NOT gate)

I have my circuit configured this way because I'll be hooking up my 8051 microcontroller GPIO pin to the point where three resistors (R2, R3, and R4) intersect, and the microcontroller only outputs my ...
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0answers
253 views

Transistor logic to drive h-bridge with negative voltage source

Shown below is a H-Bridge circuit I have used to drive the cathode of a VFD display with a source voltage of +2.4V with a +3.3V digital logic level. I have decided to switch the cathode source ...
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160 views

Proper SPDT switch wiring

Apologies in advance if this has been asked before, but I haven't been able to find anything like it. Please let me know if it has. I'm curious about the proper/standard way to connect a SPDT switch ...
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0answers
104 views

Converting BCD Truth Table to Output Functions Using K-Maps

To be honest, I'm just looking to see if I'm on the right track with a certain question. This here would be my answer for the K-Map for the "H" output function and im just curious if im on the right ...
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0answers
650 views

Worst case delay for a CMOS gate

I want to determine the input pattern for the worst case tpHL of this CMOS gate. I think there may be more than one input pattern that give worst case tpHL. The following is my reasoning: The ...