Electronics notes/Shorter-range wireless notes

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This is for beginners and very much by a beginner. It's meant to try to cover hobbyist needs, and as a starting point to find out which may be the relevant details for you, not for definitive information.

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IO: wired local IO wired local-ish IO · · · · Shorter-range wireless (IR, ISM RF, RFID) · bluetooth · 802.15 (including zigbee) · 802.11 (WiFi) · cell phone


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See also Category:Electronics.


License-Free and ISM bands and such

ISM bands were reserved partly to avoid RF communication in these bands, so that certain industrial, scientific and medical ('ISM') devices could use these frequencies without having to worry about causing interference.


The sub-GHz part of these are associated with some quite-basic things like light remotes, older garage remotes, wireless weather stations, home automation, that sort of low-data-rate use (that often deal with interference just by repeating their message a bunch) though there are newer things, like 802.15.4 (e.g. ZigBee) and LoRa using it for more complex communication.

The largest reason is probably that manufacturers do not need to buy licenses to put out products that use these ranges.

In particular 2.4GHz, where the recognizable names include WiFi and bluetooth.


There are a few other bands that are not strictly ISM but are similar in legal practice.

The most common bands seem to be:

  • 315MHz (a.k.a. 310MHz?)



  • 433Mhz, a.k.a. 434MHz
    • Usually refers to 433.05–434.79MHz, the center of which is 433.92Mhz
    • ISM band used in ITU region 1 (Europe, Africa, part of the middle east, former Soviet Union), and there may be local variations of how large this range is (e.g. in the UK(verify))
    • various devices use ~5mW-50mW of transmitted power(verify) with various antennae to reach 100m, 200m, sometimes over 1km of line-of-sight range(verify)
    • Users: various short-range household remote devices
    • LPD433 defines 69 channels (25kHz spacing) with at most 10mW


  • There are some license-free bands used largely for walkie talkies


  • 868Mhz
    • refers to an unlicensed band in Europe (not ISM, but usable under similar terms (verify))
    • The extend varies. You may see references like 868.0-868.6MHz or 863-870MHz or 868-870MHz, 869MHz, 868.35, etc.
    • Split into sub-bands, each with their own typical sort of use, limitations on transmit power and duty cycle. Some have channels, some don't. (see e.g. [1]), SRD860
    • Documents seem to contradict each other on detauls, so this probably varies per region and probably has over time as well.
      • People seem to like 869.4..869.65 MHz sub-range - it's one of the wider ones, allows the strongest transmission (500mW) and a decent duty cycle (up to 10%), if you meet certain conditions
    • Not usable in the US because of 824–894MHz mobile bands(verify)
    • One of the RFID ranges (865–868) is in/near this, though since it too is short-range it ought not to cause too many interference problems.
    • I have seen mention of 860.48–879.51 - what's this?(verify)
    • Users: various short-range household remote devices (e.g. remote controlled switches, wireless thermometers, some home automation), a few wireless mice, one variant of ZigBee, (check more (verify))


  • 915MHz
    • the common name for, and center of, the 902-928MHz band
    • ISM band in ITU region 2(meaning America)
    • Note this is close to the 935-960 MHz (or is that 872-960 MHz?) mobile band (verify)
    • not usable in Europe because of that mobile band (verify)
    • Users: various short-range household remote devices and some computer peripherals, IEEE 802.15.4 (Zigbee), (check more (verify))


  • 2.400–2.500 GHz, also referred to by its center, 2450MHz
    • Note: Microwave ovens are also right in the middle of this. Little makes it out of them, but if well-placed it may still interfere(verify)
    • Users: IEEE 802.11 (WiFi), Bluetooth, IEEE 802.15.4 (Zigbee), some short-range household remote devices and some computer peripherals, some cordless phones (verify)


See also


Simple/slow short-range wireless on 315MHz, 915 MHz, 433MHz, or 868 MHz

Radio frequency communication used for things like home automation, car remotes, some wireless mice and presenters, RF-triggered flashes in photography, and more.

Many applications need only one-way communication.


Often uses ISM bands, often 315MHz or 915MHz in the US, or 433MHz or 868MHz in Europe, simply because these are license-free bands (given you stick to some basic restrictions - mostly power output (range) and duty cycle, largely to make sure products will play nice enough with each other around).


Many of these bands have multiple frequencies/channels that specific devices may be tuned to a specific sub-ranges/channel. See also ISM band notes.


Range

For most devices the primary limits are lowish transmission power, and the (often-simple) antenna.

This is often more or less by design, to avoid causing interference.

Some things stop working at one or two dozen meters, while a few things are designed for 100m or 200m. You may be able to get 1km in ideal conditions.

Modulation

Signal modulation is often either ASK or FSK, or sometimes PSK, which are three fairly basic ways of modulating data - via amplitude, frequency, and phase:

  • ASK, Amplitude shift keying [2], often specifically:
    • OOK (the simplest and probably most common form of ASK)
  • FSK, Frequency shift keying [3], including:
    • BFSK, a.k.a. 2-FSK, is probably its most basic form
    • GFSK applies a Gaussian filter to pulses, to control its (out-of-band) bandwidth, and for more power efficiency, at the cost of some smearing between symbols (verify)
    • MSK is a type of continuous-phase frequency-shift keying, which makes more efficient use of the aether
      • GMSK adds the Gaussian filter details to MSK
  • PSK, Phase-shift_keying [4], not used much


When buying devices, the common acronyms are ASK, FSK, GFSK, MSK, and OOK.



See also:

Speed

Speed is typically low, because that's easier to do around noise, small bands, and with simpler hardware.

The simplest devices may use bit lengths of on the order of 1ms, for an effective data rates of a few hundred bits per second.

Slightly fancier designs may be listed as 4800bits/s or 19200bits/s or so, in some cases up to perhaps 256kbps or 500kbps .

...in relatively ideal conditions. A speed like 100kbits/s is already hard to do reliably.

In theory you can do more, but in practice you have to consider distance, noise, interfering senders in the same band and thereby retransmission.


Since there is no exact reference timer, line codes often use things like Manchester coding[7] or something else where bit trains are unambiguous without strict timing.

Line code, protocol

Line code specifies how exactly user data is coded on the channel. This is often designed with the physical medium in mind.

The most basic radios do not apply a line code, just mirror the state of an input pin on the aether (with whatever modulation they do), and receivers mirror that on their output pin again, maybe sending their command a few times in a row, but otherwise leave it up to simple encoder/decoder chips to fix noise issues, collission issues, or other robustness/cleverness.

Fancier radios may act more like serial ports/modems with a small FIFO buffer, and may use a coding that tries to avoid noise and timing issues.


There are many device-specific protocols - often somewhat proprietary, but often easy enough to interpret and imitate if you wish.

A good number of such applications will use a matching pair of ICs (one encoding on the sending side, one decoding on the receiver side), to encode/decode the data to whatever function they have and with specific protocol/function assumptions hardcoded.


You often see protocols use a preamble, so that the receiver can have automatic gain adjustment, without missing the start of basically all packets (since such receivers often end up adjusting to maximum gain when they hear no transmissions).

Other signals

You pretty much have to be able to deal with other senders in the same band.

There are duty cycle limitations on devices (via certification, anything you bought will adhere). This often means yours probably gets through soon enough. Things like remotes (which rarely send) may well send something a few times in with some short interval, just to increase the chance one gets through.


If you want to avoid erronously acting on someone else's data, you'll probably want to make your protocol include protocol-specific and/or product/project-specific values.

In things like home automation there are typically also per-device addresses (which you can often physically set on each device) to make devices specific to a house, or even a room or so.

Some protocol names

Within home automation, protocols / device implementations include (very very roughly from wider to more specific use):

You can often find specific details in some general-purpose DIY home automation projects.


  • Domia lite / Bye Bye Standby (BBSB)
    • there's a simple and an advanced variant of the protocol
  • KlikOn-KlikOff (a.k.a. KlikAan KlikUit (kaku) and other translations)
    • Seems to often use PT2262 (encoder) and PT2272 (decoder) ICs [8]
  • Home Easy [9]
  • Byron
  • W800RF32 (X-10 RF wireless?)
  • Conrad FS20 (868.35 AM (/915?))
    • based on house codes (8 digits?) (meant for isolation from your neighbours) and addresses (256 of them)
    • addresses are subdivided into 225 unique addresses, 15 function group addresses, 15 local master adresses, and 1 global master address -- mostly for the ability of independent and/or grouped addressing of any device
  • Oregon Scientific
    • protocol version 1.0
    • protocol version 2.1
    • protocol version 3.0
  • Ikea Koppla (434 MHz)
  • Skytronic Homelink
  • Harrison (Curtain Motors)
  • Intertechno (434 MHz)
  • Visonic
  • Flamingo
  • ATI Remote Wonder / Medion
  • NEXA
  • Waveman
  • Proove
  • Duwi
  • other devices such as thermostats, wireless doorbells, weather stations, toys, utility
    • Elro AB600 (433MHz) (dimmer?)
    • La Crosse TX3 / TX4 (weather station)



See also (unsorted)





On range, walls, and antennae

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)


RFID

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

RFID (Radio-frequency identification) refers to a radio-frequency communication.

It often refers to a few specific designs, most of which are small and fairly easily hidden, particularly in/on/as small surfaces, relatively hidden devices.


On power

There are:

  • passive RFID tags
    • which use an external source of power - often the communication itself (the reason for the large coiled antennae?)
    • can be very small and thin, and therefore almost invisibly embedded in many things.
  • active RFID tags
    • battery-powered (...so limited lifespan and more expensive)
    • can signal autonomously
    • can be used over considerably larger distances
    • can often communicate faster
  • battery assisted passive (BAP)
    • active tags that remain passive until triggered by communication


Frequency use

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Simple uses are often lower-frequency, more industrial RFID is often higher-frequency.


Sorted approximately by common use:

  • Low-frequency - 120-150kHz range
for many countries often either often ~125 and ~134.2 kHz
these are more or less interchangeable
You can fairly easily get readers (and writers) for this.
  • High-frequency - 13.56 MHz (worldwide ISM(verify))
  • Ultra-high
    • 433MHz
    • 868MHz (EU unlicensed) and ~915MHz (US unlicensed) (think ISM)
  • Microwave
2.4Hz and 5GHz - expensive tags


Criticism

See also

LoRa

LoRa uses 433 MHz, 868 MHz / 915 MHz bands and is aimed at being low power in general but also sending kilometers away, and example uses include tracking animals against poaching, tracking loan-out vehicles, utility meters.


LoRa is a physical layer, and proprietary,

LoRaWAN is a network layer on top of physical that allows routing


https://en.wikipedia.org/wiki/LoRa


802.15.4 / ZigBee

See Electronics notes/802.15 (including zigbee)

WiMAX

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

http://en.wikipedia.org/wiki/WiMAX



Bluetooth

This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me)

Works in 2.4 - 2.4835 GHz, in 79 separate 1Mhz channels, chaning channels continuously to lessen the probaility of consistent interference with other devices and other protocols (busy areas still have problems, though).

Maximum speed:

  • Bluetooth 1.1 and 1.2 versions is ~700Kbit/s,
  • Bluetooth 2.2 can reach ~1 to 3Mbit,
  • Bluetooth 3 can do ~24mbit.


IrDA

Old IrDA could do dozens of kbit/s (typically serial port speeds). Line of sight signalling, so fell out of style.

New variants can do multiple Mbits (fastest variant 1Gbit/s), and are recently seeing some different applications (e.g. fast photo transfer).

Range:

  • ~1m max, half that is typically best for speed(verify)
  • For lower power devices it's ~20cm.
  • ((verify)whether high-speed devices are shorter-range)


ANT

2.4 ISM band, simple protocol stack.

http://en.wikipedia.org/wiki/ANT_%28network%29


RC

Unsorted

ANT is a proprietary ISM-band system, lower-power than e.g. 802.15.4 (ZigBee),