RF transmitters / receivers
- Thread starter RustyH
- Start date
There is indeed a lot to choose from. RF stuff ranges from cheap "dumb" modules to more expensive smart modules. You generally get what you pay for. What you should get depends upon the application and possibly the budget.
The dumb modules are usually ASK modulated and fixed at 433MHz. These will interfere with each other as well as other devices on the same frequency, but are a good way start out experimenting with RF. Don't expect a range of more than 30 - 50 with these (some even less).
The smart modules can be configured for frequency and modulation type, have built error correction, automatic packet handling, etc, and are generally much more versatile with much greater range.( 300m to >1000m LOS)
If you just want to fiddle around then I would suggest a RX / TX pair of cheap ASK modules along with two 14M2 Picaxe's that support the RFIN and RFOUT commands. REV-ED can supply these cheap ASK modules as well as the smart XRF Modules.
What is the application ?
The dumb modules are usually ASK modulated and fixed at 433MHz. These will interfere with each other as well as other devices on the same frequency, but are a good way start out experimenting with RF. Don't expect a range of more than 30 - 50 with these (some even less).
The smart modules can be configured for frequency and modulation type, have built error correction, automatic packet handling, etc, and are generally much more versatile with much greater range.( 300m to >1000m LOS)
If you just want to fiddle around then I would suggest a RX / TX pair of cheap ASK modules along with two 14M2 Picaxe's that support the RFIN and RFOUT commands. REV-ED can supply these cheap ASK modules as well as the smart XRF Modules.
What is the application ?
jedynakiewicz
Senior Member
Rusty, it is difficult to know how to reply when you don't indicate what type of comms you are looking for, but as the previous posters replied there is plenty to choose from.
There is a lot on the forum about most of the basic units and using serial protocols, but for the state-of-the-art have a look at the new ZULU and BRAVO units recently launched by www.rfsolutions.co.uk. These units not only each contain a unique serial number that is used in pairing up, but they also are paired as transceivers rather than just a transmitter paired with a receiver. This means that when the transmitter sends a signal to the receiver it awaits a response from the receiver to let it know that the signal has been received correctly. If it hasn't been so then a flag is raised on an error output pin. Similarly, they have a "watchdog" function and talk to each other briefly every ten seconds just to make sure that the other one is there. If there is a loss of communications then this is flagged up on another output pin. The ZULU units also boast a range of 2 kilometres and use a secure data protocol. I have recently started playing with them but one thing to note is that the DIL versions have a pin-out spacing of 1.27mm, not the usual 2.54mm so there are some issues in prototyping them up on stripboard or DIL sockets etc. You can also choose between a serial link or a ten channel digital link with pin-to-pin matching on the sending and receiving units. This is very easy to patch into PICAXE because you just set a high or a low on a PICAXE output pin connected to an input on the ZULU-T and then reverse the process on a PICAXE chip at the receiver. Also, because you have a ten pin input, you can have a standalone transmitter with up to ten simple switches. You can also configure the thing for two analogue plus eight digital transmissions if you prefer.
The BRAVO units are a little simpler, have a 1 kilometre range and are more usefully pinned out at 2.54mm spacing. If you are just kicking off in this field these may be the units for you. Download the datasheets and have a look at the capability of each unit and see if it matches your objectives.
So, not the cheapest units, but certainly they do what you asked for - reliable pairing up, and they are easy to interface to PICAXE, especially if you choose the BRAVO units.
Any specific ideas on what you want to use the radio link for or are you experimenting to learn more?
There is a lot on the forum about most of the basic units and using serial protocols, but for the state-of-the-art have a look at the new ZULU and BRAVO units recently launched by www.rfsolutions.co.uk. These units not only each contain a unique serial number that is used in pairing up, but they also are paired as transceivers rather than just a transmitter paired with a receiver. This means that when the transmitter sends a signal to the receiver it awaits a response from the receiver to let it know that the signal has been received correctly. If it hasn't been so then a flag is raised on an error output pin. Similarly, they have a "watchdog" function and talk to each other briefly every ten seconds just to make sure that the other one is there. If there is a loss of communications then this is flagged up on another output pin. The ZULU units also boast a range of 2 kilometres and use a secure data protocol. I have recently started playing with them but one thing to note is that the DIL versions have a pin-out spacing of 1.27mm, not the usual 2.54mm so there are some issues in prototyping them up on stripboard or DIL sockets etc. You can also choose between a serial link or a ten channel digital link with pin-to-pin matching on the sending and receiving units. This is very easy to patch into PICAXE because you just set a high or a low on a PICAXE output pin connected to an input on the ZULU-T and then reverse the process on a PICAXE chip at the receiver. Also, because you have a ten pin input, you can have a standalone transmitter with up to ten simple switches. You can also configure the thing for two analogue plus eight digital transmissions if you prefer.
The BRAVO units are a little simpler, have a 1 kilometre range and are more usefully pinned out at 2.54mm spacing. If you are just kicking off in this field these may be the units for you. Download the datasheets and have a look at the capability of each unit and see if it matches your objectives.
So, not the cheapest units, but certainly they do what you asked for - reliable pairing up, and they are easy to interface to PICAXE, especially if you choose the BRAVO units.
Any specific ideas on what you want to use the radio link for or are you experimenting to learn more?
Thanks for all the replies
In terms of the data, its really just basic on / off commands for now, nothing fancy yet (till I learn)
But I would like multiple transmitters / receivers running (with in about 10m of each other, so I don't want 1 pair triggering a pair on a different system. Likewise, the neighbors wont be happy if the signals start interfering with the TV or wifi etc. lol
I dont know enough about RF to know if my concerns are valid
In terms of the data, its really just basic on / off commands for now, nothing fancy yet (till I learn)
But I would like multiple transmitters / receivers running (with in about 10m of each other, so I don't want 1 pair triggering a pair on a different system. Likewise, the neighbors wont be happy if the signals start interfering with the TV or wifi etc. lol
I dont know enough about RF to know if my concerns are valid
Then you may want to consider some of the 2.4GHz RF Modules from INHA0S.
RustyH: PICAXEs & 433 MHz devices are made for each other, but past forum pleas for RF help have often driven us regulars totally crazy. Please do some Googling & at least light reading of radio & antenna basics.
I strongly suggest that you build up your "hands on" PICAXE + RF skills by starting REALLY SIMPLY. Learn by doing -perhaps consider these ~US$10 a matched pair Dorji ASK modules?
Stan. (ham call ZL2APS- since 1967)
I strongly suggest that you build up your "hands on" PICAXE + RF skills by starting REALLY SIMPLY. Learn by doing -perhaps consider these ~US$10 a matched pair Dorji ASK modules?
Stan. (ham call ZL2APS- since 1967)
jedynakiewicz
Senior Member
Rusty, okay, that is clearer now. Basic on/off stuff. Why not have a look at http://www.rapidonline.com/Electrical-Power/AM-FM-System-Modules/Transmitters-Receivers and download some of the datasheets - you can a lot from browsing through these. Then, as you come across aspects that are unclear, do as Stan suggests and research the topics on the internet. A basic radio switching unit such as http://www.rapidonline.com/Electrical-Power/AM-Transmitters-and-Receivers-for-Embedded-Radio-Control-122241 will be easy to understand and to implement. You can interface the receiver to a PICAXE chip very easily and that will give you the pairing of transmitters and receivers that you are looking for, it should not interfere with any other equipment and the units will definitely not trigger each other unless you have paired them up. You can set up an arrangement with one-to-one; many(transmitters that is)-to-one(receiver) or one-to-many. All you have to do is to ground the "learn" pin on the receiver, press a button on the transmitter, watch for acknowledge LED on the receiver and the pairing is complete. The devices have all the security of a remote car lock...which is pretty much what they are! Like remote car keys in multi-story car park, the remote will trigger the receiver and not interfere with anyone else. Range is 100 metres or so, less of course inside a building.
Now that is a cast-iron way of getting the pairing etc. done for you and, as you are using certified transmitters and receivers you are safe from messing anybody else around with spurious transmissions. But that route will get a system working quickly; you may not get a lot of understanding of radio data transmission out of it. If you want to learn more about the basic methods, then buy a simple serial transmitter and receiver pair such as http://www.picaxe.com/Hardware/Add-on-Modules/433MHz-Radio-Transmitter-and-Receiver-Pair/ and match these up with the circuit kit http://www.picaxe.com/Hardware/Add-on-Modules/RF-Connect-Radio-Boards/.
If you use a simple transmitter with a serial interface you can use a preamble, referred to as a qualifier, in the serial data sent to ensure that the receiver - or at least the PICAXE that is connected to it, will only respond to the proper data. Have a look at the Serial in command in PICAXE MANUAL 2: SERIN pin,baudmode,(qualifier,qualifier...),{#}variable,{#}variable...
Then internet learn about Manchester Encoding. This is a method that reduces errors in transmitted radio data. You can find out more about this in the PICAXE datasheet www.rev-ed.co.uk/docs/axe213.pdf where you will learn about a chip that does the Manchester Encoding - the NKM2401.
Now you will understand more of the methods of sending RF data and ensuring accurate reception, this will take you into the latest PICAXE way of doing things using the RFOUT and RFIN commands, whereby the Manchester encoding is done by the PICAXE.
Also, have a look at the latest PICAXE transceivers the ERF units - http://www.techsupplies.co.uk/epages/Store.sf/en_GB/?ObjectPath=/Shops/Store.TechSupplies/Products/RFA020. These nifty little units work really well at short range.
Lots to learn, much fun to be had; good kit to be constructed! Hope this helps.
If you want to use 433MHz RF transmitters/receivers just to toggle something on/off, then a dirt cheap 433MHz transmitter module coupled with an HT12E encoder and a 433MHz receiver module(s) with HT12D decoder(s) will get you reliable communication, encoder/decoder will take care only the right receiver picks the data up. The communication is stable and the range is better then using RFOUT / RFIN. Take a look at the datasheets of the encoder/decoder modules, it is also possible to implement their functionality in picaxe.
You will see from the comments already that there is a lot of choice, some of the suggestions are easy to use, some require a fair bit of knowledge and experience to use effectively.
As your new to this, I would stick to the modules that Rev Ed sell, you should then get a fair bit of support to get your setup working.
I could make a suggestion of my own, and whilst the particular devices are capable of impressive performance (40Km LOS from a £6 module), they are not the easiest of devices to work with.
Ciseco RF modules (ERF, XRF, SRF, URF) are extremely easy to use, yes they're a bit more than a lot of modules out there but you're paying for literally out-of-the-box plug'n'play wireless serial comms.
Sold through Picaxe's main site: http://www.techsupplies.co.uk/epages/Store.sf/en_GB/?ObjectPath=/Shops/Store.TechSupplies/Categories/PICAXE/PICAXEConnect
And through Ciseco's main site: http://shop.ciseco.co.uk/rf-module-range/
The URF/ERF pair sold through Picaxe's site allow you to actually program a Picaxe wirelessly.
Sold through Picaxe's main site: http://www.techsupplies.co.uk/epages/Store.sf/en_GB/?ObjectPath=/Shops/Store.TechSupplies/Categories/PICAXE/PICAXEConnect
And through Ciseco's main site: http://shop.ciseco.co.uk/rf-module-range/
The URF/ERF pair sold through Picaxe's site allow you to actually program a Picaxe wirelessly.
jedynakiewicz
Senior Member
Okay, not easiest to work with, but a VERY impressive performance that you quote; you have me most interested and therefore, although you are not recommending them as a start-out device within the spirit of this thread, could you possibly give a link to this most interesting device that you use?
That was at 100mW and with 1/4 wave antennas, so much further with a yagi and low noise amp added.
There is a discussion of the basic stuff here;
http://www.picaxeforum.co.uk/showthread.php?23717-PICAXE-and-RFM22-RF-Beacon
And at this Dropbox location;
https://www.dropbox.com/sh/ompujkefda543w6/NXgepgXrmW
You will find a report;
Lost Model Locator MK3 - Range Testing.pdf
Which outlines the testing I did, there is code there for the TX and RX parts of a GPS equipped lost model locator based on the RFM22.
hippy
Ex-Staff (retired)
I would suggest a URF and a couple of ERF modules. That allows one to start with sending from Programming Editor Terminal via a URF to an ERF and back again which gives instant confidence that wireless is working. The URF is also useful in watching ERF to ERF comms which is a valuable tool in debugging.
The hard part with most wireless systems is getting it to do things. Great if it all just works as expected, but it can be a nightmare if it doesn't.
The hard part with most wireless systems is getting it to do things. Great if it all just works as expected, but it can be a nightmare if it doesn't.
Hi Manuka,
I apologise for asking a question about the interface between a RPi and a Picaxe, I kind of assumed that as it involved a picaxe this would be a safe question to ask in a picaxe forum.
Moderators - can you put the rule of not being allowed to ask about Raspberry Pi clearly in the forum rules please
I should also apologise for asking questions to which I dont yet know the answers for, As the picaxe system was designed and developed to aid beginners to get in to the world of micro processors and programming, I thought its forum would encourage questions to aid that learning process.
I also don't see this post as dithering around, as Ive only asked for some general advice. I am neither an electronics nor programming expert, hence a little bit of guidance is always appreciated, and to seek guidance means asking what you may deem as some pretty basic questions. I would understand your frustration if I was specifically asking you to build my project, yet I don't think I have......have I??
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RustyH: Enough posting (& this is not a RPi Forum!) - learn by doing! Best you stop pondering and instead get started with something PICAXEable that's reliable but simple.
FWIW data handling may be just a small part of the learning curve. Experience shows that a significant issue when going wireless at UHF freqs (300MHz-3GHz) relates to coming to grips with such "trivial issues" as propagation, interference, path obstruction, band regulations, power entitlements and antenna...
EXTRA: (Crossed posting). The esteemed PICAXE Forum naturally encourages questions, BUT the essence is that responses should be then followed up on. I recall past topics that have run on for 100s of tediously repeated postings. A "kid in an icecream shop" comparison often arises - old forum hands get frustrated when posters endlessly dither around and fail to make a tasting! "Mate - get stuck in" -as we say down under.
FWIW data handling may be just a small part of the learning curve. Experience shows that a significant issue when going wireless at UHF freqs (300MHz-3GHz) relates to coming to grips with such "trivial issues" as propagation, interference, path obstruction, band regulations, power entitlements and antenna...
EXTRA: (Crossed posting). The esteemed PICAXE Forum naturally encourages questions, BUT the essence is that responses should be then followed up on. I recall past topics that have run on for 100s of tediously repeated postings. A "kid in an icecream shop" comparison often arises - old forum hands get frustrated when posters endlessly dither around and fail to make a tasting! "Mate - get stuck in" -as we say down under.
The ERF modules mentioned, are serial (as in RS232) devices, so can be used to communicate between computers that support RS232.
hippy
Ex-Staff (retired)
Very likely. I am not sure how a Raspberry Pi would handle dumb RF modules but it should be able to handle any serial-based module. The Raspberry Pi has a UART ( LVTTL / non-RS232, idle high, active low ) and can support USB serial. I believe Ciseco has developed an XRF interface for the Pi and I would expect a URF to be usable via USB.
The Pi is really nothing more than just another PC so what works for a PC should work for a Pi. The Pi community can best tell you what would need to actually be done and any limitations and hurdles to overcome.
great, thanks Hippy
So really as long as I have a receiver that works on a PC (via some means), and a transmitter that works with the pic (and both the Tx and Rx are paired) then it should communicate.
One other question, just to understand if its a limitation, but if you connected a receiver to the RPi, can I have multiple Picaxe driven Tx devices talking to the one receiver, or can you only pair one Tx with one Rx?
So really as long as I have a receiver that works on a PC (via some means), and a transmitter that works with the pic (and both the Tx and Rx are paired) then it should communicate.
One other question, just to understand if its a limitation, but if you connected a receiver to the RPi, can I have multiple Picaxe driven Tx devices talking to the one receiver, or can you only pair one Tx with one Rx?
BeanieBots
Moderator
You can have one to many, many to many or many to one.
However, just like a person can talk to a crowd, a crowd trying to talk to one person can have its problems if everyone is talking at the same time.
Intelligent RF modules take care of a lot of the hassle involved but even they can become overwhelmed by too many transmitters going off at once.
However, just like a person can talk to a crowd, a crowd trying to talk to one person can have its problems if everyone is talking at the same time.
Intelligent RF modules take care of a lot of the hassle involved but even they can become overwhelmed by too many transmitters going off at once.
If you don't plan to deal with the odd possibility, it WILL catch you out sooner or later and generate a suprise.
That may not be quite as simple as you think. You'll need your reciever to deal with some command for ON and command for OFF. Do you care about where the command came from i.e. which of the possible Tx?
When there are overlapping transmits, you'll get garbage and need to deal sensibly with it (most likely ignore it).
The transmitters won't know there's been a problem, so won't know to try again. Does that matter here?
In the very worst case, garbage might look like a valid command, but the wrong one.
There are techniques to deal with this, but yes they are more complex. That's a consequence of many-to-one comms and applies just as well to wired networks as RF. Whether you need to go to that much trouble depends on the mystery application - you might not care for a TV channel switch, or you might care for a panic alarm etc.
There might be some hints in here
http://www.picaxeforum.co.uk/showthread.php?23895-New-Project-help-and-suggestions