Electronic Data Communication Overview

Transmitters & Receivers

In order to send a message it must be converted into an electronic signal that is suitable for transmitting the data over a communication medium. This is the role of the transmitter, which consists of electronic circuitry that changes the voltage levels for a wired transmission or modulates the signal for wireless transmission. Likewise, a receiver consists of electronic circuitry that recovers the transmitted message and converts it into a form that can be used (for storage, display, or transfer to some other device). Transmitters and receivers cover a broad range of electronic devices, from wired devices that use UARTUniversal Asynchronous Receiver-Transmitter, I2CInter-Integrated Circuit. Also referred to as IIC or I²C., SPISerial Peripheral Interface, Ethernet, and USBUniversal Serial Bus to wireless RFRadio Frequency, WiFi, and Bluetooth BTBluetooth devices.

A transceiver combines both the transmitter and receiver in the same device and antenna. One common example is a cellular phone that capable of sending and receiving data. Most RF modules are transceivers, such as the HC-12, nRF24L01+, RFM69, and LoRa, modules. WiFi modules (ESP-01) and WiFi Microcontroller Dev Boards (ESP8266/ESP32 NodMCU boards) are also transceivers.

Communication Channels

The communication channel is the medium by which a signal is sent from one device to another. The medium can be a wire, fiber optic cable, or free space for wireless communication. Wires are conductors that carry an electrical signal. Fiber-optic cables carry information on light waves through the cable and are mainly used for long distance calls and internet connections. Wireless communication makes use of the electromagnetic waves that propagate through free space.

Wires and fiber-optic cables are less prone to electromagnetic interference (EMIElectromagnetic Interference) than wireless, especially if they are shielded (e.g., coaxial cables). Fiber-optic cables are more expensive than electrical conductors and are typically used for industrial applications. However, wires and cables can be costly to install or inconvenient to use compared to wireless.

Modes

The type of electronic communication mode can be one-way (simplex) or two-way (half-duplex or full-duplex).

Simplex:

The communication is unidirectional one-way where only one of the two devices can transmit and the other can only receive. Examples that use the simplex mode of transferring data are a keyboard, mouse, and monitor.

Half-Duplex or Semi-Duplex:

Each device can transmit or receive, but not at the same time. When one device is sending, the other device must be receiving. An example that uses half-duplex mode is a Walkie-Talkie where two parties take turns speaking.

Full-Duplex:

Each device can transmit and receive at the same time. An example using full-duplex mode is a telephone line where both parties can talk at the same time.

Usage

USB:

USB 2.0 technically only supports half-duplex, although it can switch between In and Out ports fast enough to appear to a human to be full-duplex. The USB 3.0 specification defined a new architecture and protocol, named SuperSpeed (SS), which included a new lane for a new signal coding scheme providing full-duplex data transfers that physically required five additional wires and pins.

Ethernet:

Legacy Ethernet is half-duplex, but full-duplex Ethernet can be achieved using Ethernet switching. Full-duplex Ethernet is used in point-to-point connections between stations and requires that lines be concentrated using Ethernet switches instead of hubs or repeaters. Switched networks employ either a twisted pair or fiber optic cabling that uses separate conductors to provide independent transmit and receive data paths, which avoids collisions and increases throughput.

UART, I2C, and SPI:

For Single Board Computers (SBCSingle Board Computers) and microcontroller boards, wired UARTUniversal Asynchronous Receiver-Transmitter and SPISerial Peripheral Interface support full-duplex communication, whereas I2CInter-Integrated Circuit. Also referred to as IIC or I²C. is inherently half-duplex. However, the full-duplex capability of UART may depend on the specific implementation of the hardware or software, such as having two distinct buffers for storing data.

RF and WiFi Wireless Transceivers:

Most wireless transceivers are half-duplex because full-duplex on the same channel would have an issue with collisions or it would require the use two separate RF channels. The HC-12, nRF24L01+, RFM69, and LoRa RF modules are all half-duplex. WiFi also uses half-duplex communication. The 802.11 protocol is a time division duplex where WiFi devices that act as clients and Access Points (APA WiFi Access Point (AP) is a device that creates a wireless local area network, or WLAN, and acts as a central hub that allows other devices, such as smartphones or computers, to connect to it over WiFi.s) are either in transmit mode or in receive mode. When a WiFi device has some data to transmit, it first checks to see that no other device is transmitting before it transmits data.

Analog Signals

Analog signals are continuous so they can have an infinite number of different voltages that cover the natural variation of physical phenomenon. The simplest analog signal waveform is the sine wave shown in the figure below (this is a plot of the signal's voltage vs time).

A pure sine wave signal doesn't carry much information. If you were to listen to it in audio it would sound like a flat tone. More variation in the signal's amplitude, frequency, or phase is needed to carry information, such as the audio signal shown in the figure below. The analog audio signal coming from a microphone or output to headphones is a mixture of frequencies in the human audible range of 20Hz to 20,000Hz that varies continuously over time.

Many devices use analog signals, such as audio, video, radio communication, and the output of sensors: any sort of continuous time-varying quantity that conveys the data being collected or transmitted. Sensors can output an analog signal (voltage or current) that varies according to what is sensed. More details about analog signals can be found in the article below.

Analog Signals

Created:   12Oct2022   04:27:30   UTC 2022-10-12T04:27:30Z
Updated:   06Aug2024   20:38:51   UTC 2024-08-06T20:38:51Z
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What is a analog signal? What can you do with a analog signal? This article is an introduction to analog signals covering its usage and wave properties such as DC and AC components, frequency, and bandwidth.

Digital Signals

Binary or logic digital signals have two voltage values: usually one near the reference voltage (ground or zero volts) and the other at the positive I/OInput/Output supply voltage. The ground voltage is represented by binary digit bit 0 and the supply voltage is represented by the binary digit bit 1.

Digital signals can be pulses from a sensor/meter or represent information like numbers, text, audio, images, and video. The transmission of digital signals are more resilient to noise and interference than analog signals, and transmission errors can be detected and corrected. Digital data can also be encrypted, compressed, stored in memory, and edited. More details about digital signals can be found in the article below.

Digital Signals

Created:   19Mar2023   00:09:37   UTC 2023-03-19T00:09:37Z
Updated:   06Aug2024   03:10:58   UTC 2024-08-06T03:10:58Z
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What is a Digital Signal? What can you do with a digital signal? This article is an introduction to digital signals covering its usage and properties of the waveform, bit ordering, voltage level encoding, and timing.

Parity Check

A simple checksum algorithm is a parity check, which splits the data into words with a fixed number of n bits, then determines if there is an even or odd number of ones for each word's binary sequence, and appends this parity bit to the end of each word. The transmitter and receiver need to agree on how to interpret the parity bit result of 0 or 1. The most common is an even parity bit, which is 0 if there is an even number of ones and 1 if there is an odd number ones. An odd parity bit is 1 if there is an even number of ones and 0 if there is an odd number ones.

One major limitation with the parity check is that it cannot detect an even number of errors (bits flipped) in the binary sequence. It also cannot detect inserting or deleting bits that are zero.

CRC

A more thorough checksum algorithm would output a unique value for any kind of change in the input message. This is addressed by additionally considering the position of bits in a sequence at a cost of more computing. One common checksum algorithm used in practice is the Cyclic Redundancy Check (CRCCyclic Redundancy Check), which converts the message into a polynomial, divides it by a so-called generator polynomial, and takes the integer remainder of the division as the CRC. If the remainder is zero, the data is assumed to be error-free; otherwise, an error is detected.

There are three common types of CRCs based on their bit length: CRC-16, CRC-32, and CRC-64.

CRC-16:

A 16-bit CRC used in many applications, such as Ethernet, WiFi, storage devices, and embedded systems.

CRC-32:

A 32-bit CRC used in some file systems, network protocols, data storage, and encryption.

CRC-64:

A 64-bit CRC used in high-reliability applications.

CRCs are often used because they are relatively simple to implement in software and hardware, easy to compute mathematically, have a fixed length check value, and are good at detecting common errors that are caused by noise.

Usage

Wired UARTUniversal Asynchronous Receiver-Transmitter communication provides an optional parity bit that can be included in its data packets, but I2CInter-Integrated Circuit. Also referred to as IIC or I²C. and SPISerial Peripheral Interface does not provide any means of error checking. I2C was originally intended to communicate between components on a single board where the probability of error is very low. Also, I2C and SPI are aimed for low power devices with small instruction sets and limited program memory.

WiFi has a Frame Check Sequence (FCSFrame Check Sequence) at the end of each data frame with a CRCCyclic Redundancy Check for error detection and built-in Forward Error Correction (FECForward Error Correction), the process of adding redundant data such as Error Correction Code (ECCError Correction Code) to a message so that it can be recovered by a receiver when errors are introduced. This redundancy allows the receiver to detect a limited number of errors that may occur anywhere in the message, and often to correct these errors without retransmission.

RFRadio Frequency modules vary in their built-in capability of any error detection and correction. For example, the HC-12 RF module only has the built-in capability of appending a parity bit to the message for error detection, but you have to implement the algorithm to compute the parity bit in the software that sends the message, and there is no built-in error correction. However, the nRF24L01+ RF module has built-in hardware CRCCyclic Redundancy Check error detection, error correction, and resending. If an RF module does not have any built-in error detection, you can compute your own checksum of the message, like a CRC, and add it to the end of the message. You can also add your own error correction algorithm and auto resend in software.