John Graham-Cumming

Having got the flight computer radio working with my homebrew antenna it was time for a couple of tests: test that the radio could actually transmit over a reasonably long distance and see how long the flight computer would keep running for.

Here's GAGA-1 ready for its trip (I made a little cover for the antenna to protect it on the journey):

The capsule will get lifted to over 30km and I'm using a 10mW radio transmitter. As others have shown this works fine with line-of-sight and a good antenna. To run the test I got a helping hand from my parents who dropped me off at one end of Abberton reservoir with my Yaesu FT-790R and a Yagi antenna while they drove off to Abberton church with GAGA-1 sitting on the backseat transmitting a short RTTY message. The total distance between the two points was almost exactly 5.5km.

Got a few funny looks from birdwatchers and families as I stood there (although one person was kind enough to take my picture, see below).

As they drove away I lef…

Having done freeze tests on the Arduino, the capsule and the camera I decided I needed a test of the Mylar film inside the capsule after a discussion on the UKHAS IRC list.

The film is stuck to the inside of the capsule with a spray glue used to mount photographs (which is safe for use on polystyrene), but I suddenly wondered if it might peel off at low temperatures.

So, into the freezer for two hours. Here's the capsule with the lid off sitting in the freezer.

Two hours later there were no visible ill effects:

So, yet another test completed. This weekend's big test is a long distance (few mile) test of the main radio transmitter.

And so after much preparation and the early success in getting RTTY transmission working I soldered everything onto the custom Arduino shield that forms the flight computer, plugged it in and... it just worked!

Here's the flight computer board connected to the Arduino. The biggest item is the Radiometrix NTX2 module with a small voltage divider below it which is used to set the frequencies for the 0 and 1 values. The antenna is connected to the SMA connector bottom left.

Just above the radio is the DS1821 temperature sensor that will measure internal capsule temperature. It has an associated pull up resistor. The external temperature sensor connects to the three pin header to the right of the radio (it too has a pull up resistor).

Here's a log of transmitted temperature data received via RTTY:
$$GAGA,24.0,Error: 0, $$GAGA,24.0,Error: 0, $$GAGA,24.0,Error: 0, $$GAGA,24.0,Error: 0, $$GAGA,24.0,Error: 0, $$GAGA,23.9,Error: 0, $$GAGA,23.9,Error::C'fwyZ '/A,23.7,Error: 0…

For the first time today I tried receiving the RTTY transmitted by GAGA-1 and decoding it using DL-FLDIGI. It worked (first time!).

To illustrate the whole set up here's a little video. The radio I'm using is a Yaesu FT-790R II which I bought second-hand on eBay. This is an old radio, but it's sturdy and can do SSB at 70cm. Although it's a portable, I managed to buy one that had never been outside and it looks like it's been treated with great care. Thanks, eBay!

The flight computer is in a loop transmitting $GAGA-1 Test Transmission using 7-bit ASCII, with two stop bits, no parity at 50 baud.



Apologies for the shaky hand and blurry video. The combination of me + the iPhone's poor camera isn't great. Just listen to that lovely RTTY sound though.

For work I had to write a small script to scrape Google results to measure relative rank of my company and others that we like to track. We were looking at various search terms and where we appear in the results.

So, I decided to use Python with BeautifulSoup. I love BeautifulSoup, but I don't use Python very often, so... Python experts: criticize my code! How would you have done this better?
# Script to perform Google searches and extract the domain names of # the returned results. The order in which the domain names are # returned is used to determine a ranking between different companies. # This is the list of domains to look for in Google searches. To # search for more or different domains simply alter this list. The # order of this list determines the order in which the results are # saved. domains = [ 'foo.com', 'bar.com', 'baz.com' ] from BeautifulSoup import BeautifulSoup import urllib, urllib2 from urlparse import urlparse # Performs a Goo…

Yesterday's post contained a nice surprise: the parachute that will bring GAGA-1 safely back to ground level. It's a 36" parachute made to order by Spherachutes.

Spherachutes makes custom parachutes for model rocketry and also for high-altitude ballooning. Using their weight chart and an approximate weight of 1.1kg 2.4lb) for GAGA-1 a good size appeared to be 36". This should give a descent rate between 15 to 20 feet per second (that's rougly between and 16 and 20 kph).

Here's the parachute sitting on the kitchen table:

In the picture above you can see that there are two pieces of rope in the hole at the top of the canopy. That's the 'balloon option' provided by Spherachutes and is where the balloon itself will be attached via a few metres of strong, thin cord.

It's not possible to see the lines coming from the parachutes, but these will be attached to more thin cord which will attach to the capsule. So the parachute is deployed at all t…

One step closer to launch tonight with the completion of work on the software for the internal and external temperature sensors. I'm using the DS1821 digital temperature sensor that has an operating range of -55C to 125C (that should cover the range I'll be seeing). It's a lovely little transistor-sized device:

The DS1821 uses something called the 1-Wire protocol. Essentially, it's a proprietary networking protocol that uses single byte control packets and its own serial timing. The entire thing is detailed in the datasheet. The family of devices using 1-Wire supporting networking multiple of them on a single wire, but the DS1821 only supports one device per wire.

So, my two DS1821s are connected to two ports on the Arduino flight computer. To interface to the devices some software is needed. There is an Arduino project for this called OneWire but I had trouble getting it going and it was late so I wrote my own code. (Also, this is the sort of thing I love).

Fir…

As I've mentioned before, GAGA-1 is using Energizer Ultimate Lithium AA batteries for the camera, flight and recovery computers. A total of 12 batteries will fly: two for the camera, four for the recovery computer and six for the flight computer.

They are light, give a lot of power and work at extreme temperatures. All are great virtues for this type of activity. Two are inside the camera, but the other 10 need battery holders.

So, I've hotglued in place one six battery holder and one four battery holder. Happily, there's enough space inside the capsule for them. Before doing this I also put batteries in them and shook them as hard as I could to see if the batteries were likely to come loose.

In the picture you can also see the nylon threaded rod used to hold down the computers and camera and the cable in the middle is the coax coming from the quarter wave antenna. The coloured dots on the battery holders are part of my Murphy's Law protection scheme.

The Mylar fi…

Having dug out and insulated the hole for the camera that will fly on GAGA-1 there was one last camera-related task to perform: make sure that it didn't move during the flight.

If you've seen any videos of other high-altitude balloon projects you'll know that there's quite a lot of buffeting of the capsule (especially in the jet stream) and so the camera needs to be fixed in place.

I had been planning to use strong Velcro mounts but after shaking the capsule around it was obvious that the camera was going to move around and the pictures would be spoilt. So, Plan B.

Plan B is a M6 nylon threaded rod that pierces the capsule wall and holds the camera in place with nuts. To do that a suitable 6mm hole needs to be drilled in the camera itself.

I dismantled my spare Canon A560 (the one that's partly broken) to see where I could drill. It was pretty obvious that the safest place was right through the view finder from the front. There are no electronics in the way. …

With St. Valentine's Day on the way, here's a little story about love (and technology).

Back in 1995 I needed a laptop for my girlfriend. She was thousands of miles away in Europe and I was in California and the phone bills (and the shenanigans with messing around inside international phone switches) were getting too much. I knew that we'd be able to communicate cheaply if I paid for a CompuServe account in the US and gave her a machine that had a PCMCIA 14.4Kbps modem in it. She'd be able to dial a local call and send and receive email from me in California.

Only trouble was, I didn't have enough money to buy her a laptop. So I kept searching around for deals and happened upon a Toshiba T4800CT in The Good Guys! in San Jose, CA. It was an older model and being sold off for a reasonable price. And it was a suitable machine.

So, I decided to buy it. But I couldn't because the machine was locked. There was some software that locked down Windows completely a…

After yesterday's blog post on the state of Plan 28 I've received over 1,000 emails and messages of support for the project. Thank you so much!

I can't possibly reply to everyone personally, but thank you! It means a great deal.

Here are a sample of the heartwarming messages:
I'm in for the long haul! Get the charity set up ASAP; I want to throw money at this project. Babbage had the patience and perseverance... so do we. Just keep going! The pledge holds! Building one of these things isn't like slapping a few parts together. We knew it would be a long process. We're here for the long haul. I'll happily increase my donation in the hope you can still reach the original goal. Many people say "Why?" I say "Why not?" Go for it! Still very supportive. Send details of where to deposit pledge at any time. I'm still in for $100. I'd love to see this done and one day come to see it in person! This is a great project and I…

Yesterday, many readers will have received an email from PledgeBank informing them that the Plan 28 pledge drive had failed. In a narrow technical sense that's correct: I had hoped to get 10,000 people to pledge to donate $10/£10/€10 towards building Babbage's Analytical Engine. In the end 3,996 people from around the world pledged.

Thank you to everyone who expressed this interest in the project. Because of you the project is not going away.

Here's the current state of things:

1. I am in the process of setting up the charitable organization that will manage Plan 28. As I mentioned before I've joined forces with Doron Swade on this and we are actively working to get the project running. Tomorrow I am meeting with specialist lawyers who will handle the charity registration.

2. We are in active talks with the Science Museum about their participation in the project (we hope to build the Analytical Engine at the Science Museum). This has take much longer than anticip…