One of the coolest projects I have done so-far with my kids is a "near-space" balloon. That's not quite into space itself (100Km+) but so high that the sky looks black and you can start to see the curvature of the earth below you.

The Flickr set with the photos from our first launch is here: http://flic.kr/s/aHsjK22nDc

This is a quick-fire slideshow of the photos from the balloon, formatted as a 2.5 frames/sec video. I'm having trouble embedding it so the link is here

In order to take this kind of photo you need to send a camera up to the stratosphere. Ours went 38Km (124,000 feet) straight up. This is easy enough: you attach it to a massive balloon, let it rise until the balloon bursts (due to the v. low pressure at the edge of the atmosphere) and then it will fall back to earth.

In order to see the photos that you have taken, you then need to find the camera afterwards. This is the trick.

Fortunately, at least in the UK and increasingly across Europe, the very helpful guys at the UK High Altitude Society (ukhas.org.uk) have developed a distributed network of trackers who will receive a signal from your balloon, upload the data to a server and plot the position for you on a Google Maps based page (spacenear.us/tracker/).

In order to take advantage of this wonderful network of helpers, we need to build a tracker that will communicate with their equipment. That is what I will outline in this instructable.

There are plenty of rules and regulations regarding what you can fly and which parts of the radio spectrum you can use for various tasks. The approach I will use in this instructable is suitable for the UK under the rules prevailing in 2013. If you live elsewhere or you are doing this significantly after I write this instructable, please check the rules that apply to you. The guys at UKHAS are fantastically helpful.

So - let's build a radio-tracker.

Step 1: Things we need

The tracker is based upon the Atmel ATMeag328 Microcontroller which forms the heart of many of the popular "Arduino" boards. We are going to make an "Arduino Compatible" board which we can program using the Arduino IDE.

Because the GPS module and SD card both require 3.3v and we have plenty of computing power, we may as well make the whole tracker run on 3v3. That means that we can't clock the '328 up to its full 16MHz but it will run happily at 8MHz on 3v3, and that's plenty for our purposes.

The tracker is designed on a custom PCB which is 5 x 5 cm in size. This means that it can be fabricated on some incredibly cheap PCB fab' sites. The design files for the tracker board and more details on the design are in the later steps.

These are the materials I used for my design. There may well be better options but this worked well for me:


1 x Custom Tracker Board (see next step)
1 x ATMega 328**
1 x 8MHz Crystal (NB not the usual 16MHz)
2 x 22 pf ceramic caps
1 x Radiometrix NTX2 (e.g. from UPU's store)
1 x GPS breakout board with antenna (the board is designed for this one)
1 x SD card breakout board (e-bay)*
1 x board-mount DS1820 temperature sensor*
1 x external DS1820 Temperature sensor (e-bay)*
1 x HoneyWell HSCDANN001BA2A3 board-mount absolute pressure sensor (Mouser)*
1 x tactile switch
3 x 100nf ceramic caps
1 x 100 uf electrolytic cap
1 x MCP1825 ultra-low dropout 3v3 regulator
1K resistors (around 5)
10K resistors (2-3)
4k7 resistors (4-5)
3mm LEDs (0-4 according to preference, different colours)*
Selection of 1% resistors (I used: 47K/6.8K for the battery sensor and 6.8K/10K for the radio driver )
Male header pins (0.1") - some straight, some 90'

Soldering station and solder
Helping hands
Wire strippers

Programming / Debugging Tools:
PC with Arduino IDE installed
USB to UART adaptor (I use a cheap CP2102. FTDI would work too) or program with ISP (see below)

For Bootloading/Programing**:
ISP programmer


Arduino + breadboard or ISP shield

* - These sensors and indicators are not essential to the function of
the board but allow you to send some interesting data and log it for analysis offline.

**You can buy pre-bootloaded chips but they expect a 16MHz crystal. You would likely at least have to correct the timings in the code to make it work on 8MHz. It is certainly preferable to burn an 8MHz bootloader (see later). It's not hard to do.

<p>Could you clarify - is this using Ham Radio APRS for the downlink, or is there some OTHER HAB tracking network?</p>
<p>No,it uses RTTY to send GPS data strings and you will need to download and install DlFldigi to use the tracking map.</p><p>1- <a href="https://ukhas.org.uk/projects:dl-fldigi" rel="nofollow"> https://ukhas.org.uk/projects:dl-fldigi</a></p><p>2- <a href="http://tracker.habhub.org/" rel="nofollow"> http://tracker.habhub.org/</a></p><p>But after you build the system and get it running,go here and setup your payload as to show up on the map once your signal is received (Genpayload)</p><p><a href="http://habhub.org/" rel="nofollow">http://habhub.org/</a></p><p><a href="http://habitat.habhub.org/" rel="nofollow">http://habitat.habhub.org/</a></p><p>Do you live in the USA?</p><p>Jim,N2NXZ</p><p><br></p>
<p>Sorry,it uses the 70cm USA ham radio band 434.650 mhz USB mode.</p>
<p>did you get any gps data above 60,000 feet ? because most gps receivers have an inbuild limit above which they stop (even the ones that say they don't do ..)</p>
<p>Yes - we got full GPS data all the way up to 38km (124,000 feet). The trick is to use a Ublox GPS and set it to &quot;flight mode&quot;. They operate arbitrarily high if you do. You are right, however, the choice of GPS is critical in making this project work. I have noted that in the materials section so hopefully anyone following this will chose appropriately.</p><p>Cheers</p><p>Ugi</p>
One of the best Instructables I have seen. Don't let the complainers bring it down. I have a pilots license too, and was never scared of weather ballons that were launched daily. I sure would not fear this. You clearing it with your local Aviation Authority, and getting clear it through them is more than enough of a safeguard. Keep up the incredible work, I would love to see more of your videos. Have you done more lunches with this platform?
<p>Thank you for your comments - and for the patch!</p><p>In spite of what is implied in some comments, this is just a foam box with a radio board as described - the largest piece of metal is an AA battery. It's not a zero risk but really quite a small one. HAB launchers are also very responsible in getting permission. I have never experienced anyone suggesting or condoning launching without clearance. You apply and are given a launch window, and have to be available on a specific phone number for pilots to call if they want to know whether your balloon is up or not. Since you track it all the way by radio, you could give them exact GPS position, altitude and heading if they did call, although a launch only takes a couple of hours, of which most is spent way higher than you could possibly fly so I've not had any need for that so far.</p><p>Ugi</p>
<p>what if it makes collision with airliners ? </p>
You can only fly in the UK if you get permission. That is only given form places and wind directions away from major air corridors. Your flight is also notified to airmen and the maximum weight is quite low.<br><br>If you did actually collide, what would happen is that your payload would be destroyed with very little chance of any damage to the aircraft.
As a commercial pilot I find this terrifying and the suggestion that it would cause little damage to the aircraft arrogant. What if it breaks off a pitot tube, or rosemount or AOA probe? That little tiny chunk of metal getting sucked into the turbine would destroy it. And at altitude that kind of engine damage could be catastrophic.
<p>I didn't say that the chance was zero - there is a very good reason that HAB launches need clearance and are made away from air traffic routes with careful consideration of wind direction etc. However, in the event of a collision, the overwhelmingly most likely event is that the line attaching the balloon to the payload will break (it's 30 meters long so it's by far the most likely to take a strike). The breaking strength is controlled to be less than 10kg (IIRC) so the payload would just fall and the balloon pop up like a cork from a bottle.</p><p>I don't dismiss the possibility of causing damage but there is a lot of sky and very little metal even in the payload, which is less than one cubic foot in size. It could happen, without question, but there are many things more likely to cause problems to an plane.</p>
I really hope your big plan for safety isn't really the &quot;big sky, little airplane&quot; theory. If that method was so effective we wouldn't need TCAS, ADS-B, RVSM, not to mention ATC issuing traffic alerts and giving radar vectors to keep airplanes separated. Assuming everyone that reads this is going to head over to their local FSDO or CAA office to get permission to launch a 1 cubic foot box is just stupid; they won't. And while we train for emergencies, a metal box being injested into a motor or through the windscreen (likely killing both pilots) isn't one of them. <br><br>But have your fun and enjoy the pictures.
You are obviously going to find fault no matter what is said. If you are truly a commercial pilot, you would know that weather balloons are launched every day somewhere in the U.S. and I'm sure the UK. As he said many times, clearance is required. Just as with weather ballons, they can give you a launch window that puts it in the air when no traffic is in the area. The sky is not filled with aircraft. There are FAR more areas NOT in flight paths than are. He didn't say go launch ntext to an airport. Get over your self. I'm sure we are all impressed that you can fly a plane. <br><br>I haven't flown in a few years, since I became disabled, but getting my pilots license was one of the easiest things I have done in my life. It's not that ddifficult to fly, yes there are dangers out there when flying. However, I would in no way be concerned for this one. I got my license while in the Air Force and they launched weather ballons form a pad daily, M-F and still flew F-117a, F-4s, T-38 and German Tornados every day with no problems. We flew small aircraft at lower altitudes daily also, mainly Cessnas. Guess what..still no problem with the weather ballons. They just notified us when they were launching and we held take offs till it was clear. Not that hard.
<p>whining whining whining, just don't crash into my house...chukle.</p><p>That same thinking could have saved the DOdo bird or stopped blloms of nasty water plants into other ecosystems causing untold milliions (billions?) of damage. Then ther is Monsanto's death corn, they apparently are allowed to own the maize plant genome, even if in the process it wipes away millions of years of evolution...</p><p>bah humbug I say,</p><p>However, as a person who lives near very busy airports this whole things asks the question HAVE WE LOST OUR MINDS?!</p><p>So sometimes the sky IS falling or maybe one day a plane FALLS OUT OF IT!</p><p>oopsies</p>
<p>and of course with no doubt the whole project is so great and amazing. if i got free time i really urge to experience such project as well. </p>
<p>thank you . but i imagine if the jet engines of plane swallow it, a disaster would happen. no matter if its too small and lightweight. </p><p>the small birds in airports can kill any jet engine by sucking into it. i know the chance is very very small. but just asking. </p>
<p>The supposed policemen of the world watched 9/11 helpless. The safeguards in this fantastic instructable sound adequate. Congratulations!</p>
<p>Very nice DIY tracker Ugifer! Thanks for the effort you've put on this.</p><p>Any idea if it can be modded to use with APRS AFSK instead of the 50baud regular FSK without exceeding the 32Kb flash for the atmel?</p>
<p>Is the goal to implement AFSK on the atmel, or to interface with with something?</p>
<p>try looking at these..... </p><p><a href="http://www.byonics.com/" rel="nofollow">http://www.byonics.com/</a></p>
<p>Hi HF_ATL</p><p>Thanks for your comment - I'm sorry I missed it initially.</p><p>I am afraid I don't know the protocol for APRS but I'm pretty sure there would be enough flash space. The issue is more likely to be whether there is sufficient SRAM. If you could live without the SD card then I'm sure there would be enough of that too. However, the TinyGPS library and the SD card both use a lot of SRAM so you would need to be careful writing a sketch that uses both. That's why the telemetry includes the amount of free SRAM - for monitoring without using Serial (which itself also uses a buffer of SRAM).</p><p>Ugi</p>
<p>How do you deploy the parachute? Does it open up when the payload starts to fall, or is it deployed when it is closer to the ground (i.e. 300m or so) to minimize drift?</p>
<p>The parachute is held between the balloon and the payload. It's pulled out by the tension between them when the balloon is rising. When the balloon bursts, the payload falls and inflates the parachute.</p><p>Ugi</p>
<p>Interesting, I would have liked (and much prefered) this on a Raspberry Pi.</p><p>One then has the capability to add Sensors, Logging etc etc.</p>
<p>Thanks. It's been done with RPi's quite often but they use a lot more juice, which means you need more weight in batteries. Usually people reserve them for when they are trying to stream pictures, which is quite a task when you only have 600 baud!</p><p>The 328 can handle a large number of sensors and is well suited for driving the radio because it doesn't have a layer of operating system between the code and the pins which makes strict comparatively easy to program. Even with the radio, a GPS, two temperature sensors, a pressure sensor and an SD card, I had plenty of processing power at 8MHz. What gets tight is SRAM for data manipulation.</p>
<p>This is so cool it isn't funny. Wow! If only my old man had been this cool. Lucky kids.</p>
<p>Thanks Laral!</p><p>It's great having kids - gives me an excuse to try all the projects I couldn't justify doing for myself!</p><p>Ugi</p>
<p>That reminds me of my brother and I always saying &quot;let's do it for the kids&quot; whenever we wanted to do something that was kind of beneath our ages. :)</p>
<p>Simon, </p><p>Thanks for the Byonics shout-out! The U.K. has very strict limitations on flying trackers ( You cannot even use the Ham Band) The 433 MHZ stuff is limited to ISM ( Flea) power, and its just a coincidence that its a US Ham band too. We built a version of our old MT-300, on 434.650 for use in the U.K, and set them to run at 300 Baud, which effectively doubles the free-air range of the transmitter ( We called it the MT-FTQ, with the last part indicating &quot;For The Queen&quot; . Radiometrix has a guy in England selling the RF modules to end users ( They are kind of pricey in single units unfortunately) England is funny: You can buy a silencer over the counter ( Its considered the polite thing to do) but flying a Ham Radio will result in beheading or someother traditional monarchal punishment, and you have to have a license for a TV! You would think that a transmitter with 10 mW ERP would not work very well, and have the range of a garage door opener, but the air to ground range is enormous, even at flea power. ( People fly our 15 mW Byonics MF-15 reprogrammed as a tracker all the time, albeit into decent antennae, and they work great...while airborne) Higher power is desirable in the recovery phase, but on Islands, payloads seem to have a preference for landing in the ocean, eating your valuable Go-Pro cameras and breaking the hearts of your children. I am pretty sure this is why America insisted rater vehemently that we would prefer not to play nicely with English Law, although it may have had something to do with tea, taxes, and disarmament too....Wonderful Flight!</p>
<p>Hi Allen</p><p>It's certainly a hazard of living on a small island - I think I read that nowhere in the UK is further than 60 miles (or something) from the coast!</p>
Ugi. I'm from Montreal Quebec. I made a revolutionary concept. Maybe we can talk about it and work together ? We can Skype or FaceTime. First email me. Krystofcharles@gmail.com
<p>Hi KrystofC</p><p>Sorry - I missed your comment. Send me a PM &amp; let me know about your project.</p><p>Cheers</p><p>Ugi</p>
<p>Thaks Ugi :) </p><p>My only concern is that if the balloon lands behind a hill somewhere will it definitely be able to be located by someone somewhere, or do i need an SMS message on board that can communicate via satellite when the line of sight isn't too great. I also wondered if you knew the regulations as to how often you can transmit on 434.075MHz, as we will be constantly measuring data on board the balloon but not constantly transmitting data.</p>
<p>HI Jacob</p><p>Backup trackers are something that many people do use but without much documented success. If you are in the UK and using the centralised Google map, that will predict a landing point for you. If you lose contact fairly low then that should be enough for you to get close enough to re-establish the signal and get the exact location.</p><p>I did use a backup - an Android phone which was set up to respond to an SMS by sending its GPS location. However, because phone GPSs are generally not chosen for the ability to go higher than a cruising 747, they will often get very confused by the balloon flight (your balloon might go 3 or 4 times as high). The phone I used did respond but it took 20 minutes to reply, which was probably an hour after it had landed. We were in the car, driving home, by that point! Whether it actually had enough signal etc to respond from the field where we found it I will never know, but it might have.</p><p>There are two things to weigh-up here: you are getting a backup tracker, but it is costing you extra weight. I went with a phone because it could communicate and had a GPS but also had a camera, so I took a video of the flight using that. It was not as good as the still images but still interesting and justified the phone's trip beyond being a backup tracker.</p><p>For the 434MHz band, you can transmit continuously at up to 10mW (in the UK - I know nothing of elsewhere except that the rules vary). Your through-put is to some extent restricted by the 50-baud data-rate, which gives you a new data string every 15-seconds-ish. People do transmit at 300 and even 600 baud but generally the sensitivity is somewhat lower and there was no need for that using the data I was generating. I did test this board with 300-baud timing and it worked fine transmitting across the room. Whether it could transmit 25-miles straight-down I do not know but I believe the interrupt-based code in this instructable stands a reasonable chance if you adjust the timing in the code and the shift of the radio Of course you can always store extra data on the SD card and retrieve it later.</p><p>Ugi </p>
<p>Hi Ugi,</p><p>I have all the parts ready. But im wondering how you find the balloon once it has landed. I am doing a university project with a limited budget with a balloon, and so need a cheapish solution. Is there a GPRS arduino piece or other equipment i could use to do this? Any help you could give would be appreciated.</p><p>Thanks.</p>
<p>HI Jacob</p><p>Not quite sure what you are asking here; the point of this tracker is that it transmits the GPS co-ordinates of your balloon throughout the flight. That lets you not only find your balloon but hopefully track it right through its trip (see the images in the last step).</p><p>If you are asking how you &lt;i&gt;receive&lt;/i&gt; the signal then that is cheapest by using a Software-Defined-Radio dongle and appropriate software. There are links to that in the 'ible.</p><p>If you are launching in the UK then you are greatly assisted by a fantastic network of distributed receivers who will each upload your telemetry data to a central server where it it tracked on Google Maps. Again, see the links in the 'ible for more info.</p><p>Hope that helps. If not, just let me know.</p><p>Good luck with the flight!</p><p>Ugi</p>
<p>Hi Ugi, <br><br>Great Instructable! Just got a question about setting up the payload document on High-Altitude Balloon tracking server. Where do I find the frequency and other data the site requires to track my payload? I had a look though the code but couldn't find anything. I'm almost done making my own as you can see in the attached photo. Great work on the instructable and best of luck for future endeavours.<br>Adam</p>
<p>Hi Adam!</p><p>Looks like you have all of the essentials in there already - although there are a few more key bits I would suggest: </p><p>Next to the crystal are two 4k7s. Those are the pullups for the 12c bus - you might want to populate those. 4k7 is ideal but if you have anything between that an 10k that should be fine. Also, do you have the 22pf caps for your crystal? I don't think it will work reliably without. If you want any of the LEDs to work then they will also need their resistors.</p><p>Thanks for posting the photo - I'll send you a 3m pro-membership by PM. Love that board in red!</p><p>I would strongly recommend getting online with the UKHAS irc crowd before you fly - they have much more experience than I have and can guide you through all the remaining steps.</p><p>The frequency is set by your NTX2 - yours is 434.650 MHz. If you used the same resistors as I did to drive the NTX2 then your shift should be around 450 Hz. You can only be really sure about that by measuring it but it doesn't matter too much - as long as the central frequency and protocol is right (434.650, 50 baud, 7-bits, one stop-bit, no parity) then people can adjust the shift as needed providing it's there or thereabouts.</p><p>Let me know if you are launching in the UK - I'd love to track this one if I can!</p><p>Cheers</p><p>Ugi</p>
<p>Thanks for the prompt reply!<br>The rest of the parts are on order, most of the parts I could scavenge from my spare parts drawer, which was really handy! :D<br>Thanks for the details regarding frequency, this is the first project I'm using the NTX2, so I'm completely new to using FM transmission protocols but eager to learn. <br>Unfortunately here in Australia there's certainly less people tracking these things, but hopefully I can figure this out. I'm not on any schedule for this so baby steps for me. I think the red looks great and is a nice change to the usual green. I use <a href="http://dirtypcbs.com" rel="nofollow">dirtypcbs.com</a>, they're by far the best fabrication service I've used, definitely worth a try! Thanks heaps for the 3month membership, I'm in the process of writing a few instructables and now I have more incentive to get them done :P</p><p>I hope to incorporate this into some of my autonomous robot projects until I'm ready with the balloon. In the process of adding to the board to integrate more sensors, and possibly include an USB to Serial via FTDI so I can update the firmware whenever I need to make changes. (Adding allocations for a geiger counter, Co2 and gyroscope. Can't really justify the gyroscope but heck, why not) </p><p>Can't wait to see your future project and wish you all the best for the future<br>Cheers! </p><p>Adam</p>
<p>Love the idea of using this with a robotics platform! Even if you did most of the control of the robot on another board, you have the UART free on your ATMega so you could easily use this board to manage some sensors &amp; GPS then report back by serial.</p><p>I had a nose around dirtypcbs &amp; they look great! I have usually used iteadstudio.com . Their cheap boards are only in green but they are almost exactly the same price as dirtypcb and I haven't had a bad board yet. They do also do a 5 x 10cm board which is cheaper than paying for 10x10 at dirtypcb if that's what you need. However, I often find I need several revisions of a board once I get it working and want to tweak it, so I might well use dirtypcb so I can use different colours for different versions!</p><p>If you want to update the ATMega on-board then I use a basic CP2102 module. They are a few dollars on e-bay and just plug in to the serial pins when you need. There is a similar module using FTDI which means you don't need a separate FTDI chip on-board for each device (&amp; don't need to use surface mounted components). For a robotics board the size &amp; weight doesn't matter but if it's going up in a balloon then there's not much point in having more board area etc than you need - no PCs to interface with a 38kM!</p><p>Would love to hear what you do with these.</p><p>Ugi</p>
<p>Fantastic project, top notch instructable. Who did you use to fabricate your PCB and how much did it cost?</p>
Thanks cazpian - sorry for slow reply. I'm on vacation just now. I used Itead studio. Because the board is only 5 x 5 cm it cost less than &pound;10 including postage for 10 copies. I used slightly thinner than normal boards for weight. I think it was 1.0 mm. If you need then fast then it's more expensive because you have to pay for courier delivery. <br><br>Let me know if you make a project based on this - or if I can help at all. <br><br>Ugi
<p>This is awesome!<br>I've been looking for a tutorial like this for a while!</p><p>I have never used the radiometrix modules before, but they seem like a good solution.</p><p>What did you use for an antenna for transmitting back to the SDR?</p><p>What documentation did you find regarding the NTX2 module?</p>
<p>Hi Waymond - thanks for your comment.</p><p>The version I used has now been superseded by the NTX2B but lots of information on that and how to use it is available from UPU's web site <a href="http://ava.upuaut.net/store/index.php?route=product/product&path=71_63&product_id=92" rel="nofollow">here:</a> </p><p>The datasheet for the NTX2 is here: </p><p><a href="http://www.radiometrix.com/files/additional/NTX2B.pdf" rel="nofollow">http://www.radiometrix.com/files/additional/NTX2B.pdf</a></p><p>It is usual to use a quarter-wave ground-plane antenna, which I made from a length of 50 Ohm coax, with the braiding stripped away and soldered to a ground-plane made from copper tape on the bottom of my box a 164mm element made from the core of the coax extends below the ground-plane. The board is designed to allow direct soldering of the coax.</p><p>In the picture in the last step you can see the box I used. The drinking-straw you see supports the quarter-wave element while the little extensions on the corners expand the ground plane to a full quarter-wave in each of four directions.</p><p>Ugi</p><p><br></p>
<p>Why Arduino and microsoft? Why not Commodore with BASIC? (new commodore?) 0000 1101 is Return. 0000 1101 a BASIC program statement into into a memory line. Then type RUN. </p>
<p>I don't understand your comment I'm afraid.</p><p>I don't think Arduino it related to Microsoft - it's an independent Open Source development environment. Yes, you can run their IDE in Windows but also on a Mac or Linux box. The great thing about it is that it's a quick and easy way to program a microcontroller.</p><p>I was using BASIC on my BBC micro 30 years ago and it still runs, but it's a little heavy to send up in a balloon! Seriously thou', you could do all of this with a Pic writing in BASIC, and there may well be a BASIC compiler for the ATMeag328. I just don't know of one. I had the skills to do this with a '328 and Arduino. Others might well have preferred other systems but I don't have enough experience with those yet. You could use whatever system you preferred.</p><p>Ugi</p>
OK. This is where I am at designing a BASIC computer. 0000 1101 is ascii for RETURN. When return is pressed while writing a BASIC computer program, all the characters are then stored in a memory matrix reserved for programs. So , specifically, a flow chart for sorting program line numbers is run through. As on ATARI 2600 BASIC card the entire microprocessor program should be limited to about 1500 or so lines of binary code. JPEG or something similar would be written by other people. The small GB memory cards are JPEG (video compression matrix manipulation) format. The memory cards for PCs are secretly coded. The disc drives are fairly secret. Possibly made secret by Paul ALLEN of microsoft. The area of the us where these computers are built is san jose, not los angeles. Los angeles was where FORTRAN computers were built. FORTRAN is from the 1960's and 1970's. FORTRAN computers are more complex to build. I took apart some boards from what I think were FORTRAN computers. Many , many data busses and address busses.
<p>Do you know if this tracker would work in the U.S. and what kind of camera did you use the could stand the pressure of going up that high</p>
<p>As far as I can gather, nearly all digital cameras work fine. As long as it's in an insulated box (the blue foam box you see in the last step) it should be fine. Although the pressure is very low (8 mBar at max height in our case) as long as the camera isn't perfectly sealed it should be fine. </p><p>Light and compact is good because you don't want a heavy payload. Also using normal AA batteries is ideal because disposable lithium cells are considered more reliable than rechargeable LiPolys (although the latter do seem to work). Don't use normal alkaline batteries. They just stop working at low temperature. A Canon camera allows you to use the Canon Hackers Development Kit (http://chdk.wikia.com/wiki/CHDK) which is a good way to set your camera to take a still photo every few seconds etc.</p><p>As for the US, I don't know at all whether this transmitter would be legal. It depends upon spectrum allocation which is different in the US. Even if it is, I suspect there is not quite the same density of receivers in the US. However, you don't need many people to receive. One fixed station and one roving receiver might well be enough. My impression is that you need a amateur radio license to launch in the US. US launchers often use the<a href="http://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System" rel="nofollow"> APRS</a> network which you cannot legally use in the UK. </p><p>Good luck launching!</p><p>Ugi</p>
<p>Wow! Thanks guys - and thanks to everyone who voted for us.</p><p>The girls will be chuffed to have a prize - not that I'm excited at all myself, you understand ;-) !</p><p>Thanks again.</p><p>Ugi</p>

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