Wireless Applications

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marcos.placona

Senior Member
Hi guys, as most of you may remember, I've been working with some temperature controllers to put around my house, just as a le;arning project, and keep adding things everytime :D

Regarding the LCD that was making me mad, I decided to put it on hold for some time, as I'm talking to the manufacturer to see if I can get any help, so I shal come up with something one of this days

I was now wondering about which are the best/cheap transmitters/receivers to get the data from my devices without having to use wires. So I could have some devices around my place, and have one picaxe to get info from all them, and output on the VB6 application I've developed.

So far it get's the information, but only when connected, and I wanted to have a wireless module on each of my "external" devices.

I've read dr_acula's artivle about this, but am not really sure if it's exactly what I need.

Also, this time, I want to make sure I get something that is compatible and fully tested with picaxe, so I don't end up the same way as I did with the LCD.

Well I hope someone can point me out to something.

Update: Man those are dirty cheap, and apparently the same supplier DR_Acula used. Are they good for home applications?

http://stores.ebay.co.uk/e-MadeinCHN_Transmitting-Receiver-Modules_W0QQcolZ2QQdirZ1QQfsubZ3QQftidZ2QQtZkm
 
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manuka

Senior Member
Ranges you need? Other home interference sources (which can be IMMENSE)? In general almost any of the cheap "garage door opener" ASK 433MHz units will give 20-50m thru' walls. See many comments,tests,antenna, driving software & PICAXE circuits at => www.picaxe.orconhosting.net.nz I prefer the so called "Jaycar" units. Stan
 
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marcos.placona

Senior Member
Ranges? I live in Europe, that ain't gonna be a problem, my flat is actually 65m sq :p

Regarding home interference, so you think something like a wireless router could make some interference, or a microwave or whatever?

What do you think about the ones on eBay?

Cheers
 
hippy

hippy

Ex-Staff (retired)
Best/Cheap with Fully Tested With PICAXE is an interesting challenge.

People have certainly reported success with cheap 433MHz-style transmitters and receivers. I'd be a bit cautious with no-name Chinese imports; they may well be perfectly okay, but to start with it's best to use something from a reputable manufacturer / supplier or you could be back into the LCD problem again.

Once you're into multiple transmitters you have a problem; how to deal with transmission collisions and data corruption. That can be overcome by using XBee modules but they are more expensive and more power hungry. Either way you're likely to need PICAXE's at each sensor, although it could be possible to set XBees up in autonomous transmit mode to send back an ADC reading without a PICAXE if you used analogue temperature sensors rather than DS18B20's.

One factor which enters into it is whether the sensors can be mains/wall-wart powered or if they need to run off batteries. Any wireless system is likely to be a lot more complicated and more costly than a simple wired system.
 
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moxhamj

New Member
Indoors and 65m square = the lowest power modules will be fine. And yes, they are only a couple of dollars. And yes, they are from China but my experience is they work fine and are very reliable. They feed directly from picaxes and what goes in comes out the other end. There are transmitter modules in all sorts of power ratings and if you run out of range, just swap in a more powerful module. Just make sure you tell them whether you want 315mhz or 433.

Xbees look great but I still don't understand the instruction manual. Maybe I am missing something, but it shouldn't be complicated. I like simple - eg Stan's setup http://picaxe.orconhosting.net.nz/433rpt.jpg

There are 'pukka' modules from Radiometrix but their prices are a huge secret and I'm always concerned that 'If Sir has to ask the price, then Sir may not be able to afford our products'. Maybe that is a bit harsh but in the modern global marketplace I believe companies that advertise their prices and have online sales are going to do better.

The biggest problem is choosing a comms protocol. For simple messages 08s and 14Ms will be fine. For more complex message parsing an 18X is the minimum, but I suspect round a small 65sqm unit that complex protocols are not needed as messages will never need to be forwarded. I'd start by replicating Stan's setup.

Re the price - 1.03 pounds is a great deal. Buy a few Tx and Rx units as the shipping ends up less (I've been getting batches of 10). Don't get encoded modules - you want just the raw data going in and out. The tx units go up in price in proportion to the power. The Rx units are three types - superregen or super power saving or superhet. Superhet is about 4x more sensitive, but uses 5mA all the time. Super power saving is less sensitive but uses microamps. I'd use superhet for mains powered devices and super power saving for batteries. All the Tx units use microamps when asleep (ie when a low is applied to the data line), so batteries are definitely an option.
 
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hippy

hippy

Ex-Staff (retired)
The XBee manual is unbelievably complicated and confusing, but once configured ( and it's not too hard ) XBees are ridiculously easy to use with just SERIN and SEROUT as if they were hard-wired physical links.

I think reading the XBee manual does more harm than good. What's needed is an Idiot's guide to the XBee which explains how to set them up as I'm sure you're not the only one to baulk at using them. Page 5-8 of AXE021_XBee.PDF covers using the Programming Editor Wizard for configuration.

North Americans and Canadians are the lucky ones. The drop-in XBee-PRO XSC has just been released offering up to 15 mile LOS range, 100mW (20dBm) on 900MHz ...

http://www.digi.com/products/wireless/point-multipoint/xbee-pro-xsc.jsp
 
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Dippy

Moderator
If you don't want to support the people's army then look at RF Solutions and LPRS in UK.

If however, you are impressed with 'dirt cheap' and 'dirt cheap' is your main criterion with unknown quality and unknown warranty status then stick with 'dirt cheap' from Ebay.

Did you know that LPRS fully test every module they make? I wonder why they cost a bit more? (This was what an LPRS engineer told me. Yes, we spoke in English. Try that on CheapBay).
 
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moxhamj

New Member
I have just spent 1/2 an hour on the RF solutions website and another 1/2 hour on the LPRS website. There are some great products there. I've also spent some time trying to think of a way of diplomatically replying to Dippy's comments. I'll do the latter first.

Buying from China is not about supporting the PLA. I am a white anglo-saxon protestant born in the UK and raised in Australia. Ethnographically, I suspect I am from similar stock to Dippy. But a number of my friends at school were Chinese. My best man at my wedding was Chinese. One third of my medical school year were of Chinese extraction. When I was young products from China/Hong Kong/Taiwan were admittedly dodgy, but not necessarily any more. The industrial revolution in the UK took several hundred years and China is doing it in 10. A Chinaman does not go from a pushbike to a small car - he goes straight from the pushbike to an Audi. This is the world we live in, and if you make a living from selling widgets then it is a scary world.

So, respectfully, I don't believe saying "Buy British becasue British is Best" is necessarily going to work.

But there are other ways to approach the problem. Looking at the spec sheets for a number of the RF Solutions/LPRS modules, there are some ranges quoted that are far more than I would expect. 400 metres for 10mW for instance. How can this be? The EU seems to have a 10mW limit on power, so clearly manufacturers have to work with this, and the answer seems to be in the sensitivity of the receivers. One quoted 119db, which is far more than 93db for the 1 pound chinese module. So the solution to longer range data comms is either to up the Tx power or up the Rx sensitivity.

So, perhaps as a suggestion to the UK people making these modules, maybe this needs to be emphasised more? I wonder how many people, even on this forum, really know what 93 vs 119db means in terms of range. I'm not sure I do. If this could be explained then there is now a logical and technical reason to buy the better product.

In this case, British is Better, because the UK modules achieve longer range by talking quietly and listening more sensitively, which is a much more polite thing to do in a world of crowded RF noise.

As for the original question about "fully tested with picaxe" - I have used the Chinese modules and Stan has used the Jaycar ones. Has anyone used these UK modules with picaxes and done range tests etc? If not, anyone (hint hint Dippy) want to send a couple of samples down to the Antipodes and we can write up a good review?
 
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marcos.placona

Senior Member
Dippy said:
If you don't want to support the people's army then look at RF Solutions and LPRS in UK.

If however, you are impressed with 'dirt cheap' and 'dirt cheap' is your main criterion with unknown quality and unknown warranty status then stick with 'dirt cheap' from Ebay.

Did you know that LPRS fully test every module they make? I wonder why they cost a bit more? (This was what an LPRS engineer told me. Yes, we spoke in English. Try that on CheapBay).
Click to expand...
Dippy, dirt cheap ain't the main criteria, and that's why I asked here. Of course everybody loves a bargain, and if it does the job but is cheap, why not?

I didn't know LPRS, and even found something there that may be suitable.

I was just astonished with their delivery prices. £15.50 to Belgium (where I'm living now) and £7.50 to UK (where I used to live and still have an address).

The weight for the item is 100g, and having experience by buying/selling in UK. It's way beyond the average.

Specially 'cause I know it won't even come boxed, but bubble wrapped as most of the stuff comes when you buy over the internet.

That really makes you think twice. I'm not in favour of buying some kind of stuff from China, and when it comes to support, the phrase that comes to my mind
is "you get what you paid for".

The last time I decided not to buy something from eBay (probably Chinese stuff), I bought the LCD previously mentioned, coming from a trully European company (Germany and UK based).

Turns out that I sent an email to their support hoping for some help, as I was loosing hair quickly, and they didn't even bother about answering me. I just got an answer when I sent an email to their Sales Manager (those guys really care about their clients), and he told me he was gonna see if he could send me an example of connection, and some pic code example (nothing up to now).

So is that trouble really worth? I'm not at all going against what you say here Dippy, as most (if not all) the advices you've given me through this forum were very well accepted, and turned out to be the best sollution, so I'm really open to any considerations.
 
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Mycroft2152

Senior Member
marcos.placona said:
I was just astonished with their delivery prices. £15.50 to Belgium (where I'm living now) and £7.50 to UK (where I used to live and still have an address).

The weight for the item is 100g, and having experience by buying/selling in UK. It's way beyond the average.
Click to expand...
Marcos,

Think that is high, you should check out the Rev_Ed (UK) shipping and "handling" charges to the US!

WOW!

Myc
 
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marcos.placona

Senior Member
Right, but rev-ed is in the UK. Now, a UK company charging £7.50 to send to a UK address... That's almost what you would pay to send something much bigger.

I sold my X-Box 360 last year (came as a freebie with the mobile phone) and paid £11 to send from London to York
 
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manuka

Senior Member
I've just sent a 200g A4 envelope airmail from NZ to UK for NZ$3 (~UK£1.30) & may be persuaded to squeeze a 433 tx/rx pair in a similar posting. Stan
 
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marcos.placona

Senior Member
@Dr_Acula: I've just sent you a PM with some questions I have regarding the examples I saw on your website.

I'm not really sure you look at it in a regular basis, but can you take a look when you have some time?
 
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Dippy

Moderator
Oh me old mate Dr_Ac, I am not saying Thou Shalt Buy British. Not a lot made in UK anyway :)
I am not having a pop at the Chinese people who have been amongst the nicest people I've ever met, so please don't try and lay any xeno tendencies on me I beg of you.

I am saying that beware of anonymous cheap and not-so-cheerful - and that usually means.... check the stats.

Going straight to Ebay to save a quid can be a false economy. Often fine, but when it goes pants what do you do? The usual answer is NOTHING. You bin it and buy elsewhere, because of the hassle of sending it back to wherever. And because it's so disposable you throw it into landfill. And because the manufacturers know the returns stats they don't have to build costs into any warranty support and probably approaching zero in product testing too.

If you were a designer you want a supply of parts of consistent quality. You may want to communicate with the manufacturer or well-experienced supplier. If you were a manufacturer, obviously using bought-in components, you want quality - or do you want to have to lose half your profits on returns. Obv the real big boys can afford to have special contingencies based on statistics for this, but you get my drift.

My mentioning of LPRS was merely an example of why properly made and tested stuff is more expensive than anonymous stuff - and it rattled the cage beautifully on a dull Sunday.

And as for specs; blimey, (especially with RF) most 'range' data is given under ideal conditions with a following wind. Anyone who has worked with RF knows that and would be pretty daft to think they can pop it out of the box and get 100%. But, all things being equal I BET you $100 the specs from a respected US/UK/Euro manufacturer will be more accurate than from a cheap anonymous one (regardless of the place of majority assembly). For a one-off project that may be fine, but stick it in a product then it has to comply with the law.

Marcos, I wasn't having a go. My comments may have sounded a bit iffy. Sorry, I just worry about Ebay-itis which is an obsessive, compulsion to spend £5 to save £3 and waste 3 weeks.

And I was having a bit of joke about the PLA, but when you buy something from there do you really think the 'tax' money goes towards the Beijing Women's Institute?
 
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moxhamj

New Member
Dippy - good to "rattle the cage" on a Sunday! And good to have an intellectual sparring partner.

I agree with all your comments. And I am impressed by the sensitivities of those British modules.

I think an important point would be to distinguish between hobbyist use and use in a product that has to comply by law. Technically, Rev Ed don't even cover picaxes for commercial products and I presume most of the projects on this forum are at the hobbyist level. If a little radio module costs a pound and doesn't work then it isn't much landfill. And if it does work then alles gut.

So far, my biggest problem with RF not working/failing has been the weather - specifically water getting into electronics, and to a lesser extent, UV degradation of plastic in the harsh Australian climate. I'm currently putting together a batch of antennae that are made from pvc pipe with the modules and coax and baluns all sealed up inside and the pipe glued with PVC glue. I'll be publishing all that soon as it is another example of the theory of RF stuff working vs a practical working example.

I am aiming to get a complete 5W solar powered 1Km repeater module with battery supply for a month, 18X based, including pole, antenna etc for under $150. How so cheap? The answer is not ebay - it is a company called Electus which is the wholesale division of the well known Jaycar here in Oz. Bascially, take the Jaycar catalog and halve the prices. And this is good quality stuff.

Addit - just another thought - I wonder if Rev Ed would ever consider pairing up with a UK manufacturer of RF modules and market them on their website as "picaxe tried and tested"?
 
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Dippy

Moderator
Well, I was being a little Devil's Advocate there. I promise never to mention it again and Hope (geddit?) that Stan gets those RF Modules working to spec.

Yes, a list of 'partners' would be good.

Luckily UK sun ain't as powerful as Oz sun. Degradation is a real pain. Is complete hermetic sealing OK? Won't it get a bit hot in the sun and go pop! It's just that I note that pressure vents for serious IP enclosures are available.

I've had a real mixed bag of results with plastic in the sun (yes, even the Uk sun).
Polythene (polyethylene) was a real mix, nylon curled like a rasher of bacon, ABS seemed Ok for a while and black Acetyl Copolymer (fantastic for machining though it won't take any adhesive I've tried) behaved quite well.
But then, of course, there are some varieties of each with all sorts of anti-UV additives and life is too short to try them all.
It's a shame you can't get enclosures made from PVCu (uPVC) or can you..?
 
hippy

hippy

Ex-Staff (retired)
In defence of 'dodgy far-eastern tat', it's largely a matter of reputation and track record ( as with any other supplier ) set against potential difficulties of rectifying any problems. Recommendations such as Dr Acula's are excellent in that respect, no guarantee things will be perfect, but a lot better than chancing a total unknown.

And we mustn't forget that even the most reputable companies started without any reputation at all.

If hobbyists are prepared to take the chance, can accept the potential problems and afford to lose their money then I say go for it. I've done exactly that in buying some CF to IDE adpters - £20+P&P+VAT each in the UK, £6 for five from China all-in. Maybe the CE mark is a lie, the connectors and construction of low quality, usable lifetime minimal but it was worth the gamble. For a business, such gambles are usually not worth the risk.
 
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marcos.placona

Senior Member
Hi, thanks for all the answers, and thanks for the tips DR_Acula.

I've got just one last question.

As I'll have one receiver, and probably 4-5 transmitters. When buying the receiver, should I buy the multi-channel ones (don't really know what multi-chanel is), or the normal receiver will do? If using the normal receiver, how do I know which transmitter is sending what? Will that be by any token it sends like:

Transmiter 1 sends: Bedroom #1|23.8
Transmiter 2 sends: Bedroom #2|25

Is that theory right, or is there any other thing to do that?

And also, there's an option for 315 and 433mhz. In theory I'd say the 433 are more powerful besides being on the same frequency category, but what would make me chose between 315 instead of 433?
 
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marcos.placona

Senior Member
Wow.. that solved my questions.. I'm ready to purchase now. I'm just still not very sure about the channels thing. Why do I have normal receivers and receivers with 4 channels?
 
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manuka

Senior Member
It's easy to give PICAXE serial data streams a unique ID so that sender only is responded to. In spite of this,multiple transmitters run the risk of "signal collision" if all able to transmit at once on the same channel, & a system would need to ensure this doesn't lead to data/info loss.

It's akin to a ½ dozen users on the same 2 way radio channel - they'd have to agree not to all talk at once, OR alternatively resend at different/random moments to ensure individual messages get thru'. Multiple channel wireless uses unique frequencies for each station- handy perhaps in case of interference by a channel hog on the main frequency.

The normal 433.92MHz ISM band used by cheapie wireless data units is in fact ~1½MHz wide, & scope hence exists for multiple channels - something I'm presently investigating. Stan
 
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marcos.placona

Senior Member
Perfect Stan, I've got all my questions answered now.

Thanks to all you guys. I shall come back later with the results of my experiences.
 
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moxhamj

New Member
Yes, go for the single channel ones. Then the clever things are in the picaxe code - you can have a text header like "Bedroom1", or a unique number for each module eg "4"

There are some code examples around - you need a few "U"s eg "UUUUUU" at the beginning, then a unique word eg "Data", then a number to indicate the sending unit, then the data, (maybe a byte), then if you are really keen, a checksum byte at the end which can be a number but probably is fine to just be a letter eg "E".

To avoid data clashes, don't send data very often, maybe once every few minutes.
 
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