# Tagged Questions

Digital electronics use a finite number of states, 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.

2k views

### Why are things like RESET/MCLR active low on most ICs?

Convention? Easier to implement? Another reason? Is there a reason things like MCLR or RESET on microcontrollers are active-low, that is, you have to pull them down to reset the IC, and pull them ...
736 views

### How are logic gates created electronically?

So we have AND, NOT, NAND, NOR, OR gates, but how are they created electronically/electrically? For example, what makes NOT gate reverse the value?
653 views

### Most Simple Stoplight circuit

What would be the simplest way without using a microcontroller to make a stop light circuit. All it must do is go from Green -> Yellow -> Red.
172 views

### what is the sequence and how it is going?

I have been trying to understand the hardware implementation for booth's algorithm and here is a diagram i came across trying to explain but i didn't understand this : How it is going ? I know ...
475 views

### Can someone explain the following flip-flop circuit?

I'm having trouble understand what's going on in this circuit. The question asks "what is the value of Q if $\bar{R} = 1$ and $\bar{S} = 0$" (as shown). In this case, how can I determine ...
469 views

### How to fix my designed calculator circuit using Logisim

I am trying to design a calculator circuit that adds 2 four-bit 2's-complement binary numbers as its input and outputs an 8-bit 2's-complement number when the control bits equal 01. Here's what I ...
1k views

### Parts to build a digital camera

What kind of components are needed to build a simple digital camera? One that processes a JPEG image and can transfer over one of USB (in mass-storage mode), Bluetooth or WiFi. When could I get them? ...
258 views

### Selecting proper vales of Rb, Re and and Rbe in a NPN transistor emitter follower configuration?

I need to gate a TTL Tx pin @115000bps as the chipset that drives the RxTx lines do not implement UART BREAK for arbitrary time periods. As a quick hack I have come up with the following ...
12k views

### How to convert an expression from SOP to POS and back in Boolean Algebra?

How to convert an SOP expression to POS form and vice versa in Boolean Algebra? Eg: F = xy' + yz'
354 views

### How 1-bit was stored in Flip flop?

A flip flop is a sequential circuit and it stores a 1-bit value, but it is designed using only basic, universal gates and a feedback circuit. How then is it able to store or handle a 1-bit value? I ...
153 views

### What would be a Good Digital design learning project [closed]

What would be a good digital design project using vhdl that would require significant effort (maybe takes about 4hours/day and would take from a month to two month) as far as research and learning new ...
608 views

### What precautions should I take when mixing analog audio and digital on the same board?

What precautions should I take when mixing analog audio and digital (uC control) on the same board? I don't want to hear the I2C bus in my speakers. I'm thinking about Separate power supplies ...
649 views

### What are the advantages of using FPGAs over TTL in intro computer architecture?

I teach the one and only computer architecture course at a liberal arts college. The course is required for the computer science major and minor. We do not have computer engineering, electrical ...
2k views

### LED Quiz Buzzer Circuit With Logic Gates

I am very new to Electronics. I am Programmer and I've never done anything with electronics. However Started Using Simulators now. I want to Make Simple a Quiz Buzzer Circuit With LED. e.g. I need ...
668 views

### Why old PMOS/NMOS logic needed multiple voltages?

Why does old PMOS/NMOS logic needed multiple voltages like +5, -5, and +12 volts? For example, old Intel 8080 processors, old DRAMs, e.t.c... I'm interested in the causes on the physical/layout ...
517 views

### How to decode morse code with digital logic

I have been curious as to how one might implement a morse code decoder with basic digital logic (no microcontroller), mostly as an exercise. I could decode individual letters with a state machine, if ...
544 views

### CMOS (or CMOS compatible) shift register with latched open-drain outputs

I've been looking for a 3.3V compatible shift register (SIPO) with latched open-drain outputs. I've settled on a 74xx596 (not a '595!), but of all the 74xx CMOS series I've been looking at omit this ...
637 views

### Series vs Parallel termination load for transmission lines

I have a source with 5V 10Mhz Squarewave output, then I have an OR logic gate then 20m coaxial cable and then I have another OR logic gate. I guess I will need a matched load (now it is 100Ohm (random ...
131 views

### single-cycle design using and shared memory for both data and instruction

This is not really a question on electronics , it's more a question on logical design. I hope this is the right place to ask. How come it is not possible two use a single-cycle design and have a ...
599 views

### Edge detector - transistor only

I wonder, how can I make edge detecting circuit without using any logic IC's, using only transistors & passive components? I have digital signal with ~15ns fronts on my digital input (5v TTL), ...
462 views

### Is this a good use of a CPLD?

I am trying to generate some waveforms which are phase shifted from an input signal. The input signal is around 4.4 MHz and is a square wave at 50% duty. I need a 0 degree and 90 degree phase shift ...
261 views

### Are there any convenient “bus keeper” or “bus hold” chips?

Many CPLDs have a handy feature which will weakly drive pins toward their present state, so that a pin which is weakly pulled high will pull high and one which is weakly pulled low will pull low. Are ...
119 views

### What exactly are pins in the package?

Simple gates of the types we describe here are available in 14-pin packages (two pins of which are needed for the power supply). As it costs virtually nothing to add extra gates to the silicon ...
95 views

### Number of gates in series

Both describe EOR(XOR) gate - but according to the textbook, it says that Figure 2.17 has two gates in series, while Figure 2.19 has three gates in series. But to my eye, it seems that both have ...
1k views

### purpose of diode in this 555 timer application

I'm a newbie in electronics. I need to make a 555 timer base circuit(Refer to the schematic below) such that O/P pin of 555 is held LOW by default at power on, and the I/P pin is held initially at ...
156 views

### How can I tell if something's controlled by an analog or digital input?

Is there a way to tell if something's being control by an analog or digital input without knowing and understanding all the rest of the circuitry involved? I have a Wowwee robot (Elvis) that I'm ...
512 views

### hardware implementation of division algorithm

I have tried hard but I don't understand how this algorithm is working.Please explain the flow chart. $DVF$ is the divide overflow flip flop. $A_s$ is the sign bit of $A$ $B_s$ is the ...
627 views

### Recomendation for a digital inverter made of discrete components

I have a digital circuit in which I need only one logic inverter, and both PCB size and power consumption are serious constrains. So I thought about using a pair of complementary SMD MOSFETs (the ...
100 views

### How to encode a large number of digital input signals into a signal result

I would like to know how I can detect simultaneous pulses on several wires. Essentially I will have several wires that will serve as connection points when pressed upon. A simple visualtization of ...
380 views

### XBee and PIR sensor

I've ordered XBee wireless transceiver and PIR (motion, here is link) sensor. When I enable DIO0 digital input port on XBee with "ATD0 3" command it becomes high. I measure it with volmeter and get ...
789 views

### Syncing Signals with Global Clocks in FPGAs/CPLDs and Edge Detection

I am a newbie in digital logic design and I'm trying to get my head around syncing external signals to the global clock in an FPGA. For example, the SCK signal/clock fed to an FPGA by the SPI Master. ...
1k views

### How does this carry look ahead block work?

This is a carry look ahead adder : This adder is known to calculate one or more carry bits before the sum. From the figure we see that carry look ahead block calculates the carry C1,C2,C3,C4 . But ...
624 views

### How Does a Wired AND/OR Bus work

Studying for an exam Looking at Data buses using Wired AND and Wired OR configurations. Using tristate logic, a device is able to gain control of the bus and transmit anything down it. I don't ...
130 views

### Is this boolean expression reducible?

I have this boolean expression: F1 = a1'a2' + a1a2'. Could it be reduced even more?
78 views

### Can Transmission gates be used to implement 3 State Logic?

In my application i need to use a common line shared between two peripherals, i have to indicate to the devices whenever the bus is free or not, hence i can't have push-pull output where the output is ...
191 views

### Can someone help check my solution for this timing diagram?

I've been working on some timing diagrams and I keep mixing up the behaviors for the different flip flops. EDIT: I think I have the logic correct. If someone could please let me know if I'm ...
60 views

### How to block/allow an i2c data signal to pass on to another device

I have three devices which I'm working on and one of them needs to control i2c communication between the other two. Each of the devices is based on an AtMega or AtTiny chip. The Controller (based on ...
265 views

### graphical circuit simulator like logisim

I wanted to make a CPU and then somehow measure its efficiency/ speed. Logisim is a little buggy, and I don't think it allows you to do any sort of testing/ measurement. Does a tool like this exist?
283 views

### Does this timer circuit make sense?

I want to make a timer that counts down from 15 minutes, in 5 minute intervals. It should use 3 LEDs, and behavious should be such that when it is switched on, all 3 LEDs are lit. Then after 5 mins ...
163 views

### How can I get a broad overview of the world of electronics?

(Feel free to edit the question's title. Wasn't sure of a good one liner for my question) I'm a university student who has found a love for electronics and circuit design. I have a solid knowledge of ...
303 views

### Multiple pulses from single button press

I am working with a 74HC193 binary up/down counter, and am trying to set up a button to increment or decrement it. The procedure to increment a single step as I understand it is: Set pin 4 high ...