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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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. ...
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195 votes
8 answers
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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 ...
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1 vote
5 answers
589 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 ...
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0 votes
1 answer
646 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 (...
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40 votes
10 answers
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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 ...
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50 votes
8 answers
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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 ...
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15 votes
3 answers
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 ...
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  • 479
6 votes
5 answers
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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 ...
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  • 503
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3 answers
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?
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3 answers
420 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 ...
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  • 259
0 votes
1 answer
294 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 ...
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  • 27
-1 votes
6 answers
209 views

Simplest way to transmit digital data?

I have an interesting problem that's been wrecking my brain and would like some help with it. Basically what I have is a voltage readout box that has a few voltage displays on it. I would like to ...
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19 votes
2 answers
15k 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 (...
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4 votes
3 answers
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 ...
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3 votes
4 answers
3k 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 ...
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  • 323
5 votes
4 answers
4k views

In one-way asynchronous serial communication, how does the receiver sync up its bytes?

I want to make a serial system over RF to receive messages sent from a computer, so I can understand how digital radio works on the bare metal. The one part I don't understand is how a sender and a ...
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  • 185
5 votes
4 answers
4k 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 ...
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3 votes
5 answers
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 ...
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  • 153
1 vote
2 answers
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 ...
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  • 335
15 votes
3 answers
369 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'...
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5 votes
5 answers
912 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 – ...
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4 votes
2 answers
2k views

Bidirectional digital Isolation

I have used digital Isolators before in unidirectional Designs. I am now faced with isolating a bidirectional digital signal line. Specifically I would like to isolate the 2-wire debug interface of ...
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2 votes
1 answer
1k 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 ...
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0 votes
2 answers
685 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 ...
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  • 111
0 votes
1 answer
581 views

I2C bus arbitration - communication layer

I want to understand about the communication layer on which I2C Bus arbitration is done. My question is based on this question which was previously asked here. The accepted answer states that Bus ...
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3 votes
5 answers
1k views

Ways to send data with CRC validation

The data frames that are always sent using CRC are as follows: a CRC calculated for each byte (DATA) But to make the connection faster, could you send a single CRC for a whole frame of data? the ...
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2 votes
2 answers
10k 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 ...
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2 votes
1 answer
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 ...
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1 vote
2 answers
59 views

Indoor SISO wireless Rician channel performance

In wireless communications and when you have a SISO system, multipath is considered to be an impairment according to theory. Suppose now that we have an indoor SISO Rician channel (a strong line of ...
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1 vote
1 answer
130 views

USB Communication

is it safe to add LEDs with D+ and D- line communication? I did this schematic(attached) and the communication does not work. where is the problem?
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1 vote
1 answer
1k views

Quick digital receiver for Manchester encoded data?

I want to implement a digital Manchester encoded data receiver. The application is not dissimilar to the KeeLoq system. That is, there is no time for long link training - I want the receiver to ...
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  • 553
1 vote
0 answers
441 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 ...
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1 vote
2 answers
292 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) ...
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  • 111
0 votes
1 answer
138 views

How does MIMO increase data rate?

I understand how using multiple antennas helps improve reliability as it combats multipath propagation through redundancy. But how does using multiple antennas increase data rate?
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  • 377
0 votes
1 answer
4k 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 ...
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0 votes
1 answer
193 views

With Forward Error Correction, what bit rate should be used in a link budget?

In a typical satellite link budget, you are interested in calculating the Eb/N0, where Eb = S/R_b (Received power times the bit period) and N0 is the simply kT (noise power spectral density). ...
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0 votes
2 answers
421 views

Synchronization in digital communication

I am an undergraduate student and studying digital communication systems. I am not able to find any good resource where I can self-study about synchronization and it's types (time, frequency and phase ...
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0 votes
1 answer
334 views

Non Coherent Detection of Digital Signal [closed]

I am trying to design my first wireless digital communication system. I am going to use non-coherent procedure for detection. Say I am sending a particular bit $$T_b=5secs$$ Now at transmitting side ...
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  • 281
0 votes
2 answers
473 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 ...
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  • 173
-1 votes
1 answer
1k 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 ...
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