RF module suggestions

[elsey.jack]

Hello everyone,

I am building a weather balloon for a research project. It will be tethered and float at a maximum height of 100 M. I plan to have it transmit the temperature via radio to a hand held unit.

I was using a pair of walkie-talkies for transmitting the signal, but I think that I may have just fried one trying to modify it for my nefarious purposes.

Before I go and sink another $25 on a walkie-talkie set, does anybody have any suggestions for RF modules that I could get instead? Can you buy a paired transmitter and receiver? How expensive would such a system be?

Also, will transmitting the signal via an RF module change the frequency of the signal sent?

Thanks,
Jack

 

[lanternfish]

There have been a number of similar projects published on the interweb. However, you ar not clear as to whether or not you will be transmitting serial data ot tones.

If it is serial, a lot of people use HopeRf Tx/Rx modules. Relatively easy to interface to a picaxe and quite a bit of info on here. Use the excellent Search facility for this forum. Also, have a nosey around in the User Projects section.

Cheers

 

[elsey.jack]

I plan to use two different tones to transmit my data. Sorry for not making that clear.

 

[manuka]

Ah- now just just what height is this tether of yours allowing? That stated 100 M is not an acceptable 100 metres abbreviation, since internationally a lower case "m" is used. 100m seems pretty low unless you're checking temperature inversions/frost hollows. Details ?

Forget UHF CB. Regular 433 MHz wireless serial data modules can easily span a few 100 metres LOS (line of sight). Such tx/rx units go for US$5 -$10, & are almost a no brainer with DS18B20 sensors. Stan

 

[MFB]

You should find my post “Low Power 433MHz Telemetry System” (User-Projects, Communication section) relevant. Especially if you live in the UK and have a local Maplin Electronics store. The system is based on a pair of 433MHz transmit/receive modules that cost £9.99.

 

[elsey.jack]

Ah- now just just what height is this tether of yours allowing? That stated 100 M is not an acceptable 100 metres abbreviation, since internationally a lower case "m" is used. 100m seems pretty low unless you're checking temperature inversions/frost hollows. Details ?

Forget UHF CB. Regular 433 MHz wireless serial data modules can easily span a few 100 metres LOS (line of sight). Such tx/rx units go for US$5 -$10, & are almost a no brainer with DS18B20 sensors. Stan

The balloon will go to a height of 100 meters. And yes, I will be looking for air temperature inversions.

 

[manuka]

Sounds interesting! Details? Is this for air pollution or frost? Budget? Quite a number of techniques exist for TI monitoring as you may know. A balloon (with all it's overheads) is maybe not the most practical. Quite a common technique I've seen "down under" involves a tall "frost pole" with mounted wired sensors.

Keep in mind that the weight aloft of a powered transmitter & batteries may be an issue, & winding the balloon up & down while awaiting temp. settling may become a -brrr- chore. An alternative could be to string a bunch of wired DS18B20s up the tether - say one very 10 metres- much as on a classic frost pole. Stan.

 

[elsey.jack]

Yep, we will be looking for inversions to see their relation to air pollution. Its for a research project in the Boston area that is looking at air pollution around highways.

Helium is expensive, so one of my main priorities is keeping the weight down. I'm going to invest in a lithium polymer battery pack to keep things light.

I've done some more research and I think that I am going to go with a pair of Xbee modules to transmit the data. It seems like more of a sure thing when I have my deadline approaching. I appreciate all of the suggestions though! Thanks!

 

[elsey.jack]

Keep in mind that the weight aloft of a powered transmitter & batteries may be an issue, & winding the balloon up & down while awaiting temp. settling may become a -brrr- chore. An alternative could be to string a bunch of wired DS18B20s up the tether - say one very 10 metres- much as on a classic frost pole. Stan.

That's an interesting idea. I had my little heart dead-set on transmitting the data wirelessly, but I'll have to think about it now.

 

[manuka]

What is your budget? Is this a DIY project or for a client? ALERT: Although ZigBee is flavour of the month,XBees are both more costly & also more involved to setup. Further more they are low powered ( ~1mW), but LOS 100m ranges should be just OK. Start simply - 433 MHz wireless is a breeze in comparison, & of course you only need one way comms. See pix below

 

[elsey.jack]

What is your budget? Is this a DIY project or for a client? ALERT: Although ZigBee is flavour of the month,XBees are both more costly & also more involved to setup. Further more they are low powered ( ~1mW), but LOS 100m ranges should be just OK. Start simply - 433 MHz wireless is a breeze in comparison, & of course you only need one way comms. See pix below

Our budget is around $100-$200. This is for a university research project for which I am only being compensated for the cost of parts. Its a learning experience.

I looked at some of the 433 MHz wireless units available, but would they really have a smaller learning curve than the Xbee modules?

Hmm. Looking again at some of these units, it seems like they indeed may be the better (and cheaper!) choice. Would this transmitter and this receiver work? The picaxe has a standard maximum baud rate of 2400 bps, correct?

 

[hippy]

XBee or XBee Pro ( 100mW, up to 1 mile range ) would seem to be ideal in this case. Setup isn't difficult and they should arrive ready to work out the box. They are more expensive than 433MHz modules but are easier to use; SEROUT to one as a transmitter, SERIN from the receiver, exactly as if it were a hard-wired connection. They are also suited to working with background serial receive (HSERSETUP) and can be interfaced directly ( via MAX232 ) to a PC for testing.

433MHz is, in theory, not much more complicated but you have to add your own error checking and packetisation routines. It should be fairly easy to get transmitter code working if 'the in practice rules' on preamble etc are followed. 433MHz is often limited to 2400/4800 baud but that should not usually be a problem.

The big advantage of XBee over 433MHz is you get a bi-directional link, though that may not be important in this case. Multi-transmitter networks are much easier to deal with.

Most PICAXE support 4800 baud ( at 8MHz ) and the X1/X2 can use 115200 baud and higher.

 

[manuka]

Hippy: I'm certainly not against XBee ZigBee (& many find their setup can be involved!), but it's surely a "horses for courses" situation. For this simplex balloon need they'd be an overkill IMHO, as temps are probably only being read every minute or so. Data speed & a few duff readings hence may not be an issue, nor really is range.

PRICES: 60mW XBee Pro's are ~US$32 each & the basic 1mW XBee US$19. All manner of 433 MHz Tx & RX units abound at ~US$5 each. For simple needs I prefer KeyMark types sold "down under" by Jaycar in fact. See many mentions,circuits, tweaks & code at => www.picaxe.orconhosting.net.nz

The esteemed ( & direct PICAXE readable) DS18B20 is normally US$4, but I note them for just US$1.60 at Tayda => www.taydaelectronics.com/servlet/the-205/DS18B20-1-Wire-Digital/Detail

 

[Dippy]

Would they work? In theory, if the claims are true, they maybe fine. (Would I use them? No.)

BUT, SO much is down to your design expertise and antenna selection/positioning/hand-making/ground-planing. The performance of a perfectly adequate device can be ruined by poor application.

Just about any half-decent 434MHz Tx/Rx pair will do the job if used up correctly. (Physical and code).


The ones you linked claim 150m. No doubt that will be in perfect conditions , with the wind behind it and using a special tape measure which shrank in the rain.

I've used XBees a lot recently and it amuses me about the confusion people have with XBee/ZigBee.

As to XBee versus 434MHz.
Like Stan says, "Horses for Courses" , and I've had mixed results with ranges on standard XBees.

Downsides of XBee?
Cost. You may need the more expensive XBee-Pro.
I've had 'mixed results' with XBee re: range.
You will need to get the version with the antenna.

Upsides?
Easy-peasy. Basic radio comms doesn't get much easier.
Can change channel etc. if you have others in the area.
Bi-directional, so you could request Data from your remote device. Extra flexibility.
Could be re-used in more sophisticated projects later.


Stan loves his HOPEs and I'm surprised they didn't get a mention


Bottom Line.
You won't know whether any will work unless you get one and try it.
Your application will affect performance.
Look around for ones that claim twice the range you need - it's safer.
Go for modules that have been well researched or well known manufacturers - as opposed to the Cheapest Ch things available.
Spending the extra time searching and extra few pennies on the product could save hours wasted in testing.
I find that modules with an RSSI output more useful.
There are SO MANY better modules out there for a few extra pennies, so PLEASE don't penny-pinch. You have a reasonable budget, but don't waste it

 

[Rickharris]

For 100 meters I might have thought a kite would do the trick. Assuming normal weather conditions. A reasonable size can carry quite a load up to man carriers. No expensive gas and no relatively fragile balloon to burst or fly loose.

 

[elsey.jack]

For 100 meters I might have thought a kite would do the trick. Assuming normal weather conditions. A reasonable size can carry quite a load up to man carriers. No expensive gas and no relatively fragile balloon to burst or fly loose.

True, but what if the wind isn't agreeable? We are going to be using this thing by busy roads and we don't want anything to fall in the middle of traffic.


I want to thank everyone for their helpful advice. I've done some more research and I think that I will go with the transmitter and receiver that come with a hefty recommendation from Sparkfun. Thanks again everyone!

 

[hippy]

On XBee versus 433MHz : It is indeed horses for courses, each have their advantages and disadvantages.

On Kites versus Balloons : I'm actually planning a box kite aerial platform with PICAXE steered camera with a friend having seen how stable they are in even light wind so that is an option. I see a number of posts ( other forums ) which talk about needing lightweight loads, but for a reasonably sized kite which can pull a man off the ground that doesn't seem to be an issue ( we'll see ! ), the biggest danger seems to be the pull; get the tether wrapped round a limb and it might easily be cut off or mutilated :-O

Applicable to both balloon and ( perhaps more so ) kite; we were thinking of using data cable as the tether so we could get power and control up and composite video back down, no messing with wireless ... anyone know what the breaking strain of cat5 is ?

http://www.qsl.net/g4vgo/more_kites.htm

 

[manuka]

Ahem -kites naturally need some sort of breeze to help them stay aloft! Temperature inversions are at their most dramatic when conditions are calm & windless. During critical spring grape growth periods, many vineyards here in NZ use giant fans (or even hired helicopters) to stir the air layers when frost conditions threaten.

Elsey.jack: Given the prospect of balloons causing motorist distraction/homeland attack etc, perhaps check other TI monitoring techniques too! Ultrasonic acoustic radar may have some mileage?

Stan.

 

[elsey.jack]

Ahem -kites naturally need some sort of breeze to help them stay aloft! Temperature inversions are at their most dramatic when conditions are calm & windless. During critical spring grape growth periods, many vineyards here in NZ use giant fans (or even hired helicopters) to stir the air layers when frost conditions threaten.

Elsey.jack: Given the prospect of balloons causing motorist distraction/homeland attack etc, perhaps check other TI monitoring techniques too! Ultrasonic acoustic radar may have some mileage?

Stan.

Ha, well I'm going to make sure that we have a copy of the FAA regulations regarding moored balloons on hand for when the cops do eventually show up.

Wouldn't the use of acoustic radar require an object up in the air to reflect the sound wave back?

 

[manuka]

EJ: Acoustic reflections occur at boundaries, which for temp. inversions can be quite sharp. I don't know your academic background or project slant & level, but suggest both a Google & journal SODAR (SOnic Detection And Ranging) search. This is quite a meaty technology, being especially used with Doppler shift to identify wind sheer, & the 100s of Watts AF powers used may be illegal in urban areas. Lower freqs work best, so consider subsonic maybe? Typical publications seem => http://journals.cambridge.org/download.php?file=/ANS/ANS1_04/S0954102089000544a.pdf&code=244410c60a81ee513a840b894cced959 & => http://www.iop.org/EJ/abstract/1755-1315/1/1/012047

As an aside -during the pre RADAR 1920s-1930s most nations used acoustic devices to warn of distant aircraft. Rising aircraft speeds & radar rendered them obsolete, but I recall some of these structures are still to be found on the SE UK coast.

But a more tempting (& quieter) approach may be with radio. VHF/UHF radio waves can be enhanced (TrE) &/or ducted with temperature inversions, & under such tropospheric conditions freakish propagation can occur. TrE may be your best prospect as it's lower layer, & smog prone regions are well known by radio hams as being tropo prone. From what I recall on the higher tropo ducting (TrD), these ducts typically form at mid level (~500-1000m) & are associated with warm upper layers & cold ground (or most usually sea). Consider hence just monitoring weak nearby FM stations. or even running some point to point ~470 MHz UHF CB radio propagation measures? This'd certainly be more comfortable that standing around outdoors on a frosty eve- coughing your lungs out in the smog! Stan

 

[Wrenow]

No idea if this will be useful..... Hobby City, aka Hobby King, sells a 2.4gHz RF module for radio control transmitters for about $14 USD. The Hobby RX is about $15USD. The RF stage in the TX module is a 5v module with v+, v-, BIND, and Signal (to send standard PPM hobby radio signals). The RX is basically the same thing, but receives the signals, and has a decoder board attached. Although it is set to send about 8-9 pulses every 20MS, I have no idea what it would do with a unidirectional serial stream.

I am working on hacking it into a different RX than it was intended for, but, once set up and bound, plan to take a Picaxe and run a serioal signal to the signal pin and check with the Oscope to see hat comes out the other end of the pipe.

<USD$30 is not TOO bad a price for a pair of modules with a decent range (probably several hundred meters, if not a kilometer or more under ideal conditions). The TX board is pretty small and light, too, when stripped from the voltage regulator, bind switch, interface board. There are pictures of this module and some discussion here:
http://www.rcgroups.com/forums/showthread.php?t=1087351#post12764991

Cheers,

Wreno

 

[elsey.jack]

EJ: Acoustic reflections occur at boundaries, which for temp. inversions can be quite sharp. I don't know your academic background or project slant & level, but suggest both a Google & journal SODAR (SOnic Detection And Ranging) search. This is quite a meaty technology, being especially used with Doppler shift to identify wind sheer, & the 100s of Watts AF powers used may be illegal in urban areas. Lower freqs work best, so consider subsonic maybe? Typical publications seem => http://journals.cambridge.org/download.php?file=/ANS/ANS1_04/S0954102089000544a.pdf&code=244410c60a81ee513a840b894cced959 & => http://www.iop.org/EJ/abstract/1755-1315/1/1/012047

As an aside -during the pre RADAR 1920s-1930s most nations used acoustic devices to warn of distant aircraft. Rising aircraft speeds & radar rendered them obsolete, but I recall some of these structures are still to be found on the SE UK coast.

But a more tempting (& quieter) approach may be with radio. VHF/UHF radio waves can be enhanced (TrE) &/or ducted with temperature inversions, & under such tropospheric conditions freakish propagation can occur. TrE may be your best prospect as it's lower layer, & smog prone regions are well known by radio hams as being tropo prone. From what I recall on the higher tropo ducting (TrD), these ducts typically form at mid level (~500-1000m) & are associated with warm upper layers & cold ground (or most usually sea). Consider hence just monitoring weak nearby FM stations. or even running some point to point ~470 MHz UHF CB radio propagation measures? This'd certainly be more comfortable that standing around outdoors on a frosty eve- coughing your lungs out in the smog! Stan

My. That sounds complicated. Thanks though!

Maybe next summer.

 

[manuka]

Complicated? Isn't this a tertiary level project ?!

 

[elsey.jack]

Ha, I think that I will have my hands full just getting this balloon to work.

 

[premelec]

Semtech ICs

I was just looking at www.semtech.com RF ICs [also listed in Digikey] - not quite ready to use but definitely low prices and 433 or 900 MHz units with FSK and very good receiver signal receive and RSS specs - e.g. look at the SX1212 TXRX - so many ICs so little time!

 

[slimplynth]

On XBee versus 433MHz : It is indeed horses for courses, each have their advantages and disadvantages.

On Kites versus Balloons : I'm actually planning a box kite aerial platform with PICAXE steered camera with a friend having seen how stable they are in even light wind so that is an option. I see a number of posts ( other forums ) which talk about needing lightweight loads, but for a reasonably sized kite which can pull a man off the ground that doesn't seem to be an issue ( we'll see ! ), the biggest danger seems to be the pull; get the tether wrapped round a limb and it might easily be cut off or mutilated :-O

Applicable to both balloon and ( perhaps more so ) kite; we were thinking of using data cable as the tether so we could get power and control up and composite video back down, no messing with wireless ... anyone know what the breaking strain of cat5 is ?

http://www.qsl.net/g4vgo/more_kites.htm

I like it! during my teens, a neighbour showed me how to make box kites.

They obviously lack the wow! factor of a stunt kite but i was both amazed at the height they could reach with elegant stability and the resultant (stunning) aerial photography.

Check out the size of the box-kites on this wiki page - hang on tight