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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1answer
1k views

What does terminating I2C bus mean

I am designing a PCB which has a micro and some chips that work with I2C. I have used pull-ups (4.7 kOhm) to VCC (3.3V in my case) on the lines. Just like the picture below. I added 150 Ohm ...
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1answer
44 views

(W)CDMA, any repeating information?

I am looking to characterize a WCDMA channel to study the effects of multi-path. In order to do this I need to be able to find some repeating information (bit sequence) being transmitted by a station. ...
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2answers
79 views

Relationship between dynamic range and number of samples

I am working on an NI measurement system. I tried to measure the dynamic range of the system and I got about 100 dB. On this system I can easily change the number of samples per average (for example,...
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1answer
34 views

wirelessHD using with FPGA

I going to make a system to transfer data between 2 FPGAs wirelessly with high rate. I found that wirelessHD method can do this, now what is the required hardware to establish such system?
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1answer
1k views

Trouble using I2C on ESP32 to read temperature/humidity sensor (SI7020)

I am trying to read a temperature and humidity sensor (SI7020) using I2C on the ESP32. I modified their example code to read just from one slave device (0x40) but some commands do not work. I tried ...
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3answers
2k views

50 Ohm Single Ended Signal Impedances on PCBs

I have a basic understanding of transmission line theory and how 50ohm traces are designed on a PCB. I was wondering what the origin of this 50ohm impedance is. Are single ended digital signals on ICs ...
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4answers
857 views

Intersymbol interference vs aliasing

I was trying to figure out if ISI in time domain is similar to aliasing in frequency domain? Are these two phenomenon dual of each other? It would be of great help if someone could explain this.
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1answer
78 views

Is there a network mapping tool for path-loss?

I am not sure if this is the proper forum. I am looking for a tool to evaluate the wireless network performance.For example, given a map where should I put a transmitter/or transmitter plus repeater ...
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2answers
193 views

Efficiency of FIR filter in verilog language

Implementing a 4-tap FIR unity coefficients, is this code efficient in power and area ? ...
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1answer
120 views

Digital Communication Codification

All of the digital communication protocols I know, are built on the principle of the minimum distance, error detection and error correction. There are some protocol able to detect and or correct "...
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5answers
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What does “shift keying” mean in the context of digital modulation?

English is not my native language and I do not understand why the words "shift keying" were used to describe some types of digital modulation. What does "keying" mean in the context of signals and ...
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4answers
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Why amplitude modulation is not used for sending digital data?

It seems to me that the most simple way of modulating a digital signal is using amplitude modulation. When the signal has the amplitude 0 the bit is 0 and when the signal has some amplitude then the ...
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1answer
270 views

Mixing CAN nodes with and without transceivers on one bus?

I can see based on the answer to this question that it's possible to make a short/slow CAN bus without using transceivers and a differential bus. This brings up (at least for me) an interesting ...
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2answers
72 views

Pulse Shaping Inquiry

I am really confused about how several books and videos handle Pulse Shaping.In order to avoid ISI (Inter Symbol Interference: Energy from one sample leaking into the energy of the other, creating ...
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1answer
149 views

How does single coax wire transmit a lot of information? [closed]

I have a coax cable entering my house. The cable (from the Cable company), splits into a Cable modem (for computer network) and into a DVR (a.k.a. cable box). How can a single coax wire contain ...
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1answer
93 views

Is i2c the right protocol for this sensor?

I have a project I'm working on that involves an nrf51822 communicating with the optical sensor from a mouse. The pinout of the opical sensor seems similar to the ADNS2620, but the exact datasheet is ...
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2answers
68 views

Interference between signals having OFDM and DSSS modulations

If there are two signals, one having OFDM modulation and other one having DSSS modulation occupying the same bandwidth and over the same part of spectrum, will i be able to demodulate both signals ...
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3answers
134 views

Is the Signal-to-Noise ratio arbitrary?

It looks to me that the Signal-to-Noise ratio (SNR or S/N) is completely arbitrary and it's set by the user according to his preferences. Sorry I am amateur on the subject but I don't see any ...
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2answers
1k views

How can I interface a Raspberry PI GPIO to an open collector circuit to send / receive data?

I have a GPIO from a Raspberry PI connected to a Nintendo 64 system like so: From what I've gathered and observed, the data line on the N64 system is an open-collector output. The line is tied high ...
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0answers
66 views

Place of matched filter in fiber optic communication

In short-haul communication via optical fibers, we use photodiodes (PD) to detect the light. So if we want to use a matched filter, should we use it before the PD (optical domain) or after the PD (...
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1answer
420 views

How does the Nintendo 64 detect a controller is connected?

To give some context, I am trying to emulate controller input to the N64 via a GPIO pin on the Raspberry PI. In an attempt to accomplish this, I have one of the PI's GPIO's in a pull-up configuration ...
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2answers
259 views

By data processing inequality, by processing we are losing information. So why do we process the data?

From data processing inequality(DPI) we know that if \$Z=f(Y)\$, then \$I(X;Z)\leq I(X;Y)\$. However, in the application, we process the data. For example, we pass the received signal via a matched ...
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1answer
92 views

How to represent binary for differential and Menchester coding?

I have some questions with solution provided from random material, but I can't understand well. Question 1: I tried to represent binary for each block according to description in the picture above, ...
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2answers
128 views

Correct definition of transition in line coding

Hello I have following question and it says: I basically cannot understand this solution. My questions: isn't it a sequence of 4 0s followed by 4 1s? (answer says 4 1s followed by 4 0s) since ...
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2answers
77 views

High speed data interface for upto 5 meter

I have to interface two processor boards sitting at a distance of about 5 meters away. The data transfer rate is about 128 MBps (Mega Bytes per seconds) or 1 Gbps(giga bits per seconds). Which ...
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2answers
79 views

What are bus reliability method? [closed]

Busses provides to IC the ability to communicate to each other. But this communication can be blurred due to noise coming from or outside the circuit. I know there is ways to lower the impact of ...
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1answer
129 views

Symbol rate and optical bandwidth relation

I am quite new to the field of optical communication, so perhaps this question is so easy. In reading some papers I have faced to the concept of optical bandwidth. For example, they say the symbol ...
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3answers
128 views

Long range communication for a wearable device

We are building a wearable device for low resource settings and are trying to figure out a way to be able to send the data collected over a long range say 5-6 miles at a base station/hospital. What ...
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1answer
1k views

nand gates inverter

There are 2 ways to use 2 input nand gates as a inverter. I know one of them, which is make 2 inputs connected to one input signal. simulate this circuit – Schematic created using CircuitLab ...
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3answers
117 views

Medium-Distance Travel of Electrical Pulses over a Wire

I'm building a small morse code chip as a fun project, and I have a question about sending pulses over a wire. I was planning on using some speaker wire to connect a few of these PCBs over a somewhat ...
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1answer
493 views

How can I add a digital pulse generator to a simple LED circuit?

I have a digital pulse generator in the lab (http://www.thinksrs.com/products/DG535.htm). I want to control a simple LED circuit (battery, resistance and diode) using this digital pulse generator. I ...
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3answers
588 views

Scrambler with all zeros on input

Several communications standards use LFSR-based self-synchronizing (multiplicative) scramblers that are never reset to an initial state after initial power on. For example, 10GBASE-R Ethernet ...
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2answers
2k views

Difference between PuTTY Serial and Modbus

I am trying to communicate with a PM810 power meter using Modbus-RTU protocol with the RS-485 standard over 175 meters of CAT5e STP cable. It's less than ideal, but it's the situation I'm working with....
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1answer
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understanding a SPI data sheet - FIFO size versus recieve register size

My question is in relation to the difference between a SPI recieve register size and a FIFO. For example - I am looking at the SPI datasheet for 2 devices (1) a spi IP for an FPGA and (2) the SPI ...
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11answers
6k views

Alternatives to a classic DIP switch

I'm looking for a part that enables a user to frequently change a configuration. Right now I'm utilizing a SMD DIP switch connected to an I2C I/O expander. What bothers me is the large footprint of ...
3
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3answers
2k views

what is the span of an optical fiber?

I am new to the fiber-optic communication systems, and in reading some relevant papers, I faced to the term "span length" (such as long-span link) which I cannot distinguish it from the length of the ...
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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 ...
3
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0answers
166 views

bearing ambiguity resolve (direction finding) for multiple sources

I am working on wideband direction finding algorithms for passive sensors. I started with Music algorithm. For practical reasons, the spacing can not be maintained lambda/2. For greater antenna ...
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1answer
289 views

Determining the bit rate on a real-time USRP implementation

I'm transmitting a 16-QAM signal using an NI 2920 USRP. Here is a snapshot of the front panel that is seen (on LabVIEW) - I'm trying to figure out the bit rate from the given details. The symbol rate ...
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2answers
116 views

LC Oscillator in Capacitive Divider Mode

Hi, In oscillator circuit, I have faced such LC topologies where between two capacitors, the wire is grounded as shown above. What I don't understand is why I should ground it. Clearly at the ground ...
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1answer
225 views

A query on (7,4) Hamming Code

I have a query on (7,4) Hamming code. The generator polynomial for this is \$g(x) = x^3 + x + 1\$. The non-systematic code for the message signal \$m(x)\$ is \$c(x) = m(x)g(x)\$ The above procedure ...
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1answer
329 views

send TTL pulse from Arduino at a distance of 10m reliably?

I am trying to send TTL pulse(HIGH and LOW, each a second wide) from Arduino reliably at a range of 10m. Is there anything I need to keep in mind while wiring such as current levels, wire types etc? ...
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1answer
277 views

BPSK and ULTRASOUND [closed]

I need to design a system which will allow me to transmit data via ultrasound. I'm using BPSK modulation, the transducer frequency is 40Hz and the chipping frequency is 5kHz (however I can easily ...
0
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1answer
321 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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2answers
718 views

How to use TMS570 microcontroller UART to communicate to another device

I am trying to use a TMS570 to communicate to another device through UART. (The pin diagram is here: http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=SPNU611) I tried ...
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4answers
437 views

What communication protocol does this pinout match? DATAP, DATAN, CLKP, CLKN, CLKSEL

I am trying to build a laser diode driver circuit using a part from Analog Devices. (The datasheet is here for your reference: http://www.autex.spb.su/ad/ADN2848.pdf) It appears that there are 4 data ...
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2answers
8k views

What is the difference between PAM and PCM?

What is the difference between Pulse Amplitude Modulation (PAM) and Pulse Code Modulation (PCM)? Both seem to be effectively sampling an Continuous Time (CT) analogue wave and converting to a ...
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3answers
5k views

What is a Patty Code?

In my digital logic lecture today, my professor introduced a symbol code called Patty Code. I copied this table off the whiteboard: | Symbol | Binary | Odd Patty | Even Patty | |--------+---...
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3answers
685 views

BER vs SNR measurement in a Digital communication system

To analyse the performance of any communication system, BER vs SNR graphs are used. For a digital system like this one (Assume there is only one signal, so mux & demux are not required) SNR is ...
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4answers
2k views

'FEC limit BER' in communication systems

What is the maximum BER that a FEC can correct? In one of the IEEE papers the value mentioned was 10^(-3). My question is when FEC can correct BER upto 10^(-3) then why do many communication systems ...

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