Questions tagged [digital-communications]

Related to all communication systems that use a given digital sequence as an interface between the source and the channel input.

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35
votes
4answers
8k views

I2C 3.3 to 5.0 V conversion

I'm trying to interface a 3.3V I2C device to a 5V Arduino. I don't have any problem with SCL line. I can use a simple voltage divider but I have an issue with the SDA line as this is bi-directional. ...
191
votes
8answers
34k views

Why does USB have 4 lines instead of 3?

USB specifies 4 pins: 1. VBUS +5V 2. D- Data- 3. D+ Data+ 4. GND Ground Why is this not 3? Could the Data and Power not share a common ...
37
votes
10answers
19k views

SPI or I2C: which to use for a longish bus

I'm contemplating a project that would require several AVRs talking to each other over a bus. They'd be separated by as much as 6 feet. It seems like both I2C and SPI can let a series of micros ...
48
votes
8answers
8k views

Why is digital serial transmission used everywhere? i.e. SATA, PCIe, USB

While looking at SATA, PCIe, USB, SD UHS-II it struck me that they are all the same: digital serial bitstream, transmitted using differential pairs (usually 8b/10b coded), with some differences in ...
4
votes
3answers
5k views

UART Receiver Sampling Rate

I am trying to create a UART receiver in Verilog for my FPGA. I was following this guide http://www.fpga4fun.com/SerialInterface4.html According to it the standard practice for asynchronous ...
0
votes
3answers
1k views

Sampling Rate Passband Signal

What is the maximum/minimum possible sampling rate for the signal to be full recovered for a passband signal?
0
votes
4answers
84 views

What is the exact difference between synchronous and asynchronous serial transmission?

I'm having a hard time understanding the exact distinction between synchronous and asynchronous serial because different sources have confusing description. For example, some source say a separate ...
0
votes
3answers
363 views

PIC24f Get Clock Signal for external Device?

I have an external memory device with pin configuration: Data Input Data Output Connection System CLock DC 24V Ground Here is the link I need to design a code to communicate with this device. I am ...
0
votes
1answer
260 views

WPC Communication (Modulation)

I have found this image and wonder how to calculate or determine "Cm", because I like to simulate this circuit in LTSpice. Also should I use a Mosfet or a voltage controlled switch? Can someone help ...
15
votes
3answers
4k views

How can over 24 GHz communication be possible?

I read the article Google wants the US' wireless spectrum for balloon-based Internet. It says to use over 24 GHz frequency spectrum for communication. Is it ever possible to generate that high ...
18
votes
2answers
14k views

transmitting 5v signal over a long cable

I'm seeking for help here as I need a reliable answer to this. I need to get an input signal (low frequency 5v digital pulse), to a micro-controller from a (...
4
votes
3answers
20k views

Constellations in Digital Communication

What is the intuitive way of understanding concept of constellations in digital communication? I know the Gram Schmidt Procedure, Orthonormal basis functions and how to find the constellation but just ...
3
votes
4answers
2k views

How much binary data is transmitted across a physical wire in one clock cycle?

How much voltage change, what I'm calling binary data, can be transmitted over a wire at one time in one clock cycle? I understand, I think, binary data is what we call it and the wire doesn't really ...
3
votes
5answers
3k views

Transmission of a digital signal over a medium

A digital signal is said to have a infinite bandwidth. If a transmission medium cannot have infinite bandwidth then how can a digital signal be transmitted over such mediums? Please correct me if I ...
1
vote
3answers
3k views

How to increase range of zigbee?

I have a Zigbee Pro with Arduino whose range is 2 miles as per specifications. But practically its maximum range is only 200 meters. I am using XCTU software. Is there any setting/configuration in ...
5
votes
4answers
3k views

How does sender and receiver clock time periods synchronize in data communication?

In asynchronous data communication, Initiation of data communication between two stations(sender and receiver) involves synchronizing their clocks to ensure both stations are agreed upon same bit ...
15
votes
3answers
352 views

Communication among briefcase halves

I'm building a small laptop-ish device in a briefcase. Imagine the green wires aren't there. The LCD half lies somewhat deeper in its case than the keyboard part. For now, testing and programming, I'...
5
votes
5answers
871 views

What happens when two digital circuits are connected and one is powered but not the other?

Assume the following, generic, configuration in which two digital circuits are interconnected but have independent power supplies (e.g. two redundant microcontrollers). simulate this circuit – ...
2
votes
1answer
860 views

SN65176 RS485 contention

I am transmitting RS485 via: Mono application -> Linux USBTTY device -> RS485 adapter with an added 100R terminator -> ~1m CATV -> SN65176 with an added 100R terminator -> PIC. Via debugging I am ...
0
votes
2answers
2k views

Signal to Noise ratio problem

A 200mv peak to peak sinusoidal signal is applied to an ideal 12 bit A/D converter, for which Vref(v p-p full scale) is 5v. Find signal to noise ratio. This is a problem worked out by one of my ...
0
votes
2answers
496 views

Optical communication module using LED and photodiode or sensors [closed]

I'm trying to build a wireless communication system using LED and photodiode sensors. The communication distance is at most a few meters away, and the communication speed can be around 10kbps or even ...
2
votes
1answer
1k views

A circuit to prevent parasitic powering of FT232RL by MCU, will it work?

In a previous question I asked how to prevent the MCU TX pin (3.3V when idle) from powering an FT232RL Usb to Serial chip via the TX line: Preventing parasitic powering of FT232RL by ATMega328P I ...
2
votes
2answers
8k views

What is The Difference Between PAM And ASK

In Digital Communication can We use PAM in place of ASK The Diagram is Given as The Book Later Talks about Symbols. I Don't Understand, in PAM we don't have specific signal as input like in ASK we ...
1
vote
0answers
414 views

How to amplify a signal containing square pulses at milivolts to a couple volts

I was on it for a time. I'm planning to generate a signal containing square pulses from a smart phone's audio output. As I can get any shape of audio signal from smartphone's audio output, I want to ...
1
vote
2answers
229 views

How does widening the frequency band allows us to make faster pulses in a radio link?

I’m new to radio communication and completely ignorant in the topic. I spent some time writing software which includes calculation of the channel capacity (in bits/second or symbols/second or bauds) ...
0
votes
1answer
493 views

Data encoding for GFSK wireless

We are designing a RF link (2GFSK) using the CC1125, to replace and older system. The older system uses NRZI data encoding with bit stuffing. Bit stuffing is used to remove the present of stop flag (...
0
votes
2answers
85 views

How to switch an LED using logic 0 and 1

The PL2303HX is used to convert USB serial bridge controller. I would like to connect an LED to TXD pin so that it lights when it is logic 1 and off when it is logic 0. PL2303HX PL2303HX datasheet ...
0
votes
1answer
3k views

Digital Level Shifter with Op-Amp

I'm trying to design a simple level shifter to read the digital output of a sensor into a beaglebone GPIO. The sensor output is either 0V or the 24V supply voltage, although a different supply voltage ...
-1
votes
1answer
862 views

HDB3 Waveform: Determining the bit sequence

I was asked to determine the bit sequence of a given HDB3 waveform. I understand that if there are three consecutive 0's then the fourth in that sequence must be a violation pulse. In this example ...