433MHz for beginners

cravenhaven

Senior Member
I've noted with interest the recent posts about cheap 433MHz transceivers and am interested in getting involved, mostly because of a recent acquisition of a solar/electricity power meter and an interest in capturing the data from my weather station.

However, upon little bit of research I noticed that there are a few different protocols used by these modules aka ASK, FSK, OOK and wondered if this means that the different modules are incompatible with each other.

I gather that weather stations generally use ASK, but I dont know what the power meter will use.

Is there a 1 stop solution for these projects and other potential 433MHz communications projects or are they chalk and cheese to each other?.

Also what are the advantages/disadvantages of the different protocols?.

Thanks Allan
 

manuka

Senior Member
This is rather akin to asking about different types of cars/wine/women! Extensive 433MHz forum ponderings have arisen,so suggest searching this for the collective wisdom.

For simple work ASK is quite OK, BUT software encoding can be every involved on some commercial 433 MHz devices & may prevent modules talking to each other.

My advice is to start simply - VERY SIMPLY- for which Chinese Dorji ASK RX/TX modules are often well suited. Jaycar sell something similar, but at a much higher price. Stan.
 

eggdweather

Senior Member
ASK - Amplitude Shift Keying the data byte 10101010 sequence would modulate the RF a bit like this: High RF;Low RF; High RF;Low RF; High RF;Low RF; High RF;Low RF; Systems like this are susceptible to noise

FSK - Frequency Shift keying the data byte 10101010 sequence would modulate the RF a bit like this: 433.2MHz; 433.1MHz;433.2MHz; 433.1MHz;433.2MHz; 433.1MHz;433.2MHz; 433.1MHz; systems like this are most reliable because when data is being sent there is always a carrier to keep the receive quiet and are less susceptible to noise.

OOK - On-Off Keying the data byte 10101010 sequence would modulate the RF a bit like this: Carrier; No Carrier; Carrier; No Carrier; Carrier; No Carrier; Carrier; No Carrier; systems like this are susceptible to noise because when there is no carrier in the OFF period a noise spike can be read as data.

It's best to buy a matched pair so the modulation method is compatible. There is no standard and data modulation techniques of commercial equipment are usually complex containing addressing, error detection and correction usually through check-sums and follow modulation techniques that are less susceptible to noise.

Note that most receivers will not transfer a binary static state, thy work on signal transitions. So for example if your data source is logic 1 then receiver end can be a logical 0 and if the data source moves to a 0, the receiver end will do nothing, but if the data source moves from 0 to 1 then there will be a momentary transition from 0-1-0 at the receiver. Only when there is a continuous bit-stream above a determined data input repetition rate will the data stream at the output match it. Many systems employ a preamble of 0101010 to get the receiver stable then they send data. So data is only transmitted on transitions and is often called PSK - Phase Sensitive Keying.

As manuka says, this is a big topic, but in general with a matched Rx/TX pair they just work. the Best kind have a super heterodyne receiver as their receiver selectivity is narrow and matched to the transmitter. An example is a superhet style receiver will generally only receive a single frequency, so you can have multiple Tx and Rx pairs, but the cheaper wide-band models receive all tx'ers and so rely on the data encoding to detect the correct channel from the mass of transmitted signals and then determine the data source. This is an example: http://www.ebay.co.uk/itm/315MHz-433MHz-Wireless-Super-Heterodyne-Remote-RX-Receiver-Module-107dBm-/131574430405?var=&hash=item1ea2727ac5:m:m7n2x-eI6-uyLpx7m2tde_g
 

cravenhaven

Senior Member
Thanks all for the replies, they really cleared things up for me. I wanted clarification that the different protocols are incompatible between receivers, but didnt realise that it was a whole can of worms behind the scenes :).

Manuka, I had intended to buy the Dorji modules but then discovered that they supply both ASK and FSK types (as well as others)
Eggdweather, That explanation really cleared things up for me. I had a fuzzy understanding of the differences but it is now much sharper.
Ibenson, that link and its offshoots clarifies the depth of the task I am about to undertake.
 

srnet

Senior Member
Bear in mind that a protocol would normally be used to describe the data format, the structure of data and how one device knows what to do with the data it receives.

AFSF, FSK and OOK are really just transmission methods, and often completely independent of the 'protocol'

So you could have a heater controller talking to a boiler with a specific data structure or protocol, but it could use any of the transmission methods to do so.
 

manuka

Senior Member
FWIW: Although most 433 MHz transmitters can handle a wide supply range, this is traditionally not so for 433 MHz receivers & many annoyingly demand a tight 5V supply.

The industry trend to lower voltages favours more versatile 3V capable types -Jaycar's new ZW-3102 receiver pleasingly accepts a supply between 2.4-5.5V. This PT4302 engined SpiritOn RXN3-B module works well with the "powerful" Dorji 25mW transmitter. An easy RSSI tap can suit "sniffer" applications too.
 

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cravenhaven

Senior Member
Srnet, I dont think it is quite as clear cut as you imply, however I did struggle with finding a term that implied collectivism within the 433MHz space but also allowed for the disparate nature of the "methods". However I think its splitting hairs and accept your correction.

Manuka, am I correct in my reading of the data sheets that the Dorji DRA886RX modules also tolerate a wide supply voltage (3.6-5.5 stated in the datasheet).
I have ordered both so will look forward to some experimenting.

Thanks all for your help
Allan
 

SAborn

Senior Member
On average they will tolerate 3.6-5.5v, this is often for the transmitter, and you will find the Jaycar ones are basically the same in voltage ratings, the lower voltage rating often means a lower power output factor for the transmitter to comply with country standards.

They will work at 5v but may exceed the allowable power output set by our standards. (they would be shocked if they ever visit myself :rolleyes:)
 

srnet

Senior Member
One type of 433Mhz ISM band wireless device that rarely seems to get a mention are the data packet capable transceiver modules such as those based on the Si4432, Si4463 and SX1278 RF devices.

These modules can be cheap, less that £2 delivered in the case of the Si4432 type and provide significantly enhanced and more robust performance to the simpler AFSK and OOK modules (in my opinion).

The downside is that they need more complex PICAXE software to drive them, but once this is in place you can under good conditions get reliable packet based communications over 10s or 100s of Kilometres. In addition most of the above can be persuaded to transmit FSK RTTY or AFSK RTTY, for very long distance Amateur radio use.

The SX1278 (LoRa) device in particular is capable of extreme long range, but in addition will work reliably in situations where there is a great deal of RF noise or interference, a common situation these days and one which simple AFSK or OOK devices just cannot cope with.
 

manuka

Senior Member
srnet: Agreed, but keep in mind that this topic relates to "433 MHz for beginners"...
Although often appealingly cheap, many swish modules can be a R-E-A-L challenge to configure and drive.

I'm also a huge fan of LoRa™ (see my Instructable) , but it involves terms unfamiliar to many, and setup may take ages for even old hands to comprehend.

Extra: Microchip's RN2483 LoRa™ module has recently received an industry thumbs up.
 

manuka

Senior Member
OC71: Is your 100m loS (Line of Sight) or thru' buildings/terrain ? Local 433 Mhz interference a potential issue ? I've used those Dorji 2 way transceiver modules & caution that they may be an overkill for intro. work at short range. IMNSHO the golden rule for 433 MHz/PICAXE data work should be to start V-E-R-Y simply! Stan.
 

OC71

New Member
@ manuka,
The receiver will be in a wood-framed house and the transmitter will be 70m away with a couple
of trees in between.
When you said "start very simply" did you mean that the SX1212 may be difficult for a beginner
to set up?
 

manuka

Senior Member
That module (which uses the Semtech SX1212 RF transceiver IC) is actually a Dorji DRF1212D10 . As 433 MHz data modules go it's quite simple, but setup may still be daunting - see the Dorji manual.

OK on "70m thru' a wooden house & a few trees". Simple ASK modules may handle this, & with the receiver indoors an antenna could be used to improve performance too. Best you specify just what you're measuring/controlling- a weather station maybe ? Have you tried a commercial one ?

You really need to mention data rates intended, local interference issues, power drain & supplies anticipated. Do you really need 2 way data links (half duplex) or will just one way (simplex) do ? Stan.

EXTRA: I've long recommended folks lash up a simple 433 MHz band "sniffer" receiver & suggest you consider similar. This greatly helps in investigating "is my $#@#$% transmitter working" uncertainties,signal coverage and woes arising from local interference.
 

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srnet

Senior Member
srnet: Agreed, but keep in mind that this topic relates to "433 MHz for beginners"...
The title of the thread '433MHz for beginners' is fairly clear.

Even beginners need to appreciate the range of possibilities for 433Mhz communications.

Whilst the AFSK\OOK modules can be easier to program, that does not necessarily mean the better modules are 'difficult'.

I would be interested to hear from anyone who has actually tried to use the likes of the Si4432 or SX1278 in native mode. Understanding what goes on inside the module can certainly be difficult, but is the code really that hard to use ?
 

manuka

Senior Member
"Learn to walk before you climb"- two wheel skills should first be developed on a push bike rather than a motorbike!
 

SAborn

Senior Member
Hi,
I am also looking for transceiver modules that are good for 100 meters and easy to
set up with Picaxe, as I am new to all of this.
Will these fit the bill?

http://www.dx.com/p/low-power-sx1212-embedded-data-radio-modem-rf-transceiver-module-orange-gold-362284#.VpictilIiM9
If you want a transceiver module that will work with picaxe and requires no special code in picaxe other than simple Sertxd and Serrxd commands, and have the transceiver connect to the picaxe programming port (serial in and serial out) with 5v and ground, then the best transceiver is the Dorji DRF4432D201-L1, the module has a built in RS232 so all the signals are the correct way around to work with picaxe comms.

http://www.dorji.com/docs/data/DRF4432D20I.pdf

The module has a very good range with around 400m that I have tested to, I have had them in a tin shed transmitting into a solid brick house well over 200m in all weather conditions and never missed any data.

The other module that works well is the DRF4432D201-M2, (Also compatible with the DRF4432D201-L1) but this module do not have RS232 so would need to be used with Serout and Serin commands, both modules have the same range and use the same setup tool.

Personally I like the simplicity of the DRF4432D201-L1 with RS232 and just plugging it into the picaxe com port, as these pins are often not used with the average picaxe project other than to program the chip, so adding a wireless module takes no extra pins than what the programming socket would normally use.
 

OC71

New Member
Thanks everyone.
@ SAborn, the DRF4432D201-L1 appears to be just what I'm looking for but I cannot find them for sale anywhere.
 

SAborn

Senior Member
OC71,

Go direct to Dorji and purchase through them, although the minimum freight charge can make it costly for just 2 modules.
I will send you a PM with contact details for Dorji, so check your private messages.
 

AllyCat

Senior Member
Hi,

Dorji have a "presence" on ebay. If it's not exactly what you want, an email may persuade them to list it. ;)

Cheers, Alan.
 
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manuka

Senior Member
New Year gesture: Dorji kindly sent me diverse review products a few years back, & I'm open to freely moving many on to good homes. Let me know! Postage from NZ to exotic regions may however be an issue ...

Check the attached pix below for my stash - some were evaluation versions & may not be final products. Although the basic ASK TX/RX retain ongoing appeal (as do the SX1278 based Lora modules),surging hardware progress means I'm unlikely to use the once esteemed 4432 again.

FWIW -Semech based Lora™ devices (both Dorji's & other makes) now improve 433/868 MHz data performance by a near order of magnitude. In built up areas LoRa™ ranges typically stretch to several km (versus mere 100s of metres for even the best GFSK),along with greater reliability & lower supply drain. Others with demanding applications should recognize this trend too!

PM me if interested - Stan. (Wellington, New Zealand)
 

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AllyCat

Senior Member
Hi,

Yes, thanks for that link to some nicely documented information. But....

In his RS232 serial tests he states that: "the default state is HI, so the transmitter is running between bytes". That might be alright provided a separate "Transmitter Enable" signal is also used, but for a typical "Data Only" interface (likely to be used by PICaxers) is arguably illegal (because the ISM Band regulations specify a maximum "duty period" of typically only a few percent), and certainly is not "friendly" to other users. :(

Cheers, Alan.
 
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