Electronics notes/Shorter-range wireless notes

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This is for beginners and very much by a beginner.

It's intended to get an intuitive overview for hobbyist needs. It may get you started, but to be able to do anything remotely clever, follow a proper course or read a good book.


Some basics and reference: Volts, amps, energy, power · Ground · batteries · resistors · changing voltage · transistors · fuses · diodes · varistors · capacitors · inductors · transformers · baluns · amplifier notes · frequency generation · skin effect


And some more applied stuff:

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


Sensors: General sensor notes, voltage and current sensing · Knobs and dials · Pressure sensing · Temperature sensing · humidity sensing · Light sensing · Movement sensing · Capacitive sensing · Touch screen notes

Actuators: General actuator notes, circuit protection · Motors and servos · Solenoids

Some stuff I've messed with: Avrusb500v2 · GPS · Hilo GPRS · JY-MCU · DMX · Thermal printer ·


Audio notes: microphones · device voltage and impedance, audio and otherwise · amps and speakers · basic audio hacks · digital audio · noise reduction · multichannel and surround ·


Less sorted: Common terms, useful basics, soldering · Arduino and AVR notes · ESP series notes · PLL · signal reflection · pulse modulation · electricity and humans · resource metering · Microcontroller and computer platforms · SDR · Unsorted stuff

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 best known bands seem to be:

  • 13.56 MHz (center of 13.553 MHz ~ 13.567 MHz)
worldwide
e.g. NFC
  • 315MHz (a.k.a. 310MHz?)
(mostly US/Canada) (verify)
not ISM(verify)


  • 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)
there are be local variations of how large this range is (e.g. in the UK(verify))
not usable in other regions
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
Europe: PMR446 at 446Mhz
US: FMR and GMRS at 462 and 467MHz


  • 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 (center of 902..928 MHz)
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)



Lesser known:

  • 27.12 MHz (center of 26.957 MHz .. 27.283 MH)
  • 5.8 GHz (center of 5.725 GHz .. 5.875 GHz)
  • 24.125 GHz (center of 24 GHz .. 24.25 GHz)
  • 61.25 GHz (center of 61 GHz .. 61.5 GHz)



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 makes thing more robust around noise, with simpler (and therefore cheaper) hardware. and means you need a smaller band (which sometimes helps certification).

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)






RC aircraft and such

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)


On the airplane control-protocol side, we have

PWM
length of pulse sets position - in milliseconds
the oldest, most standard, and often a default
each channel has a wire on the receiving end, which is a bit chunky
CPPM
PPM means position of pulse sets position
the C basically means it's defined to let you send all channels over a single wire (timesliced, 20ms frames)
not sure why they didn't use PWM in such a framing, it might've been less work?(verify)
S.BUS (developed by Futaba)
digital
Spektrum sattelite (verify)
digital


Note that PWM and PPM in this context actually refer using these modulation types in a somewhat more specific standard. This is why elsewhere you'll find them called "RC PWM", "RC PPM"



http://pages.cs.wisc.edu/~bolo/rc/radio_types.html

http://users.belgacom.net/TX2TX/tx2tx/english/tx2txgb1.htm

http://rcarduino.blogspot.com/2012/11/how-to-read-rc-receiver-ppm-stream.html


https://robotics.stackexchange.com/questions/4456/pulse-position-modulation-as-used-in-rc-controls

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)


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, and the like


LoRa is a physical layer, and proprietary, so it's a somewhat specialized yet useful thing.

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),