Field testing Windsond

Last Friday evening we made the sixth field test of Windsond. We obviously already have some experience with it but this was the first test of the final circuit board and there’s always usability kinks to work out.

We connected the battery to the sond and closed the plastic bubbles that protect the electronics. The computer with connected radio dongle picked up the signal directly. The computer program made a sound every time a data packet was received to let us know the connection was good. (This feature is turned off by default.) We inflated the balloon with helium and attached with a thread to the detachment mechanism on the sond. After a minute or so, the sond made a sound to let us know the GPS fix was good enough.

Windsond and me

We let the balloon go after this brief photo shoot. It sailed away to slowly become a dot in the sky, and then invisible to the naked eye. The computer told us it was still ascending. 10 minutes and 40 seconds after start, the balloon reached 1000 meters altitude, the default top altitude. This was at a ground distance of 2651 meters, giving an average ground speed of 4.1 m/s and ascent speed 1.6 m/s. Previously we’ve filled the balloon more for a higher ascent speed. The radio connection was still good but since we’ve previously used the radio link at 5 km distance with no problem, we expected the connection to be strong.

A few seconds later, the sond released from the balloon as planned. It fell at a leisurely 4.7 m/s and continued to drift 647 meters with the wind during the free fall. During the fall, we lost radio contact with the sond. I had tested the sond with lower output power earlier and it might still be configured for lower power. I sent a command to the sond to increase output power again. This did the trick and we had good contact with the sond for the rest of the fall, down to 65 meters above ground. Due to lag in GPS updates, the real altitude was probably lower and the cut-off was caused by tree tops getting in the way. Still, this gave us an accurate GPS position of the landing site.

The pin shows the landing site. The difference in wind direction is discernible from the shape of the flight path.

A mapping application on a smartphone translated the coordinates to a patch of forest about 3 km away. We drove there and I took a hike into the forest to recover the electronics. A trip of 350 meters each way, according to GPS. I brought my netbook along and about 230 meters from the site, I started receiving radio updates from the sond again. This confirmed the coordinates. A smartphone GPS application provided a compass needle that pointed towards the position which took out the guesswork of the hike even though the vegetation was thick. Some 10 or 15 meters from the coordinates, I heard beeping from the sond and could walk right up to it. It was laying next to a spruce. The envelope cushioned the impact well and nothing was damaged.

All that remained was to disconnect the battery, walk back to the car and study the generated graph of the winds up to 1000 meter altitude. In a real situation, we would use the graph as soon as the balloon reached the peak altitude but for this test retrieving the sond was more important. The plan was to make a hot air balloon flight later that evening but the wind picked up so we chose to postpone the flight.The computer software could use some polishing but all in all, Windsond is ready for live action now. After this confirmation, we’re starting to make more of the sonds.

Website launch

Photo copyright bayasaa

Since starting working full-time at Kiwi Embedded in April, I’ve focused on technical development and didn’t have much to show. Now it’s time to launch this website and make my work a bit more public.

For a start, I’m presenting Channel Wizard and Windsond (see earlier posts). I also have a couple of other projects in various phases of development. These will be announced when mature enough.

The coming weeks will bring a mix of holiday and development work. Highest priority is to ship Channel Wizards to waiting customers. Then in mid-August I’ll go to the World Hot Air Balloon Championship to use Windsond for the two Swedish teams.

Announcing Windsond

During the last six months, I have cooperated with the hot air balloon club Ballongveteranerna to create an electronic solution to measuring winds at low altitudes, called Windsond. The development is sponsored by the Swedish Airsport Federation.

Wind conditions are of paramount importance for hot air ballooning, where the balloon drifts with the wind. The only means of flight path control lies in choosing the altitude. Interestingly enough, the wind direction and speed can differ a great deal at different altitudes so precise control is possible for a skilled pilot.

Windsond consists of a GPS, battery, microcontroller and radio transmitter. By attaching a Windsond to the small pilot balloon, a computer with a radio receiver can track the ascent without human involvement and present graphs of wind speed, direction and temperature. Once the sond reaches an altitude of 1000 m, it detaches from the balloon and slowly falls to the ground where it beeps and blinks to assist recovery. So far, we have released three balloons with Windsond. The software can be further polished but system basicly works well. Good radio reception was demonstrated from 2 km altitude and 5 km ground distance.

In mid-August, we will travel to the World Hot Air Balloon Championship  to use Windsond for the two Swedish teams. The championship will transpire in Battle Creek, Michigan, USA.

I will continue to improve Windsond to offer it as a commercial product for reusable, cheap and easy low-altitude weather measurement.

Also see the dedicated Windsond page.

Channel Wizard produced

The first microcontroller project I started was to add more channels to transmitters for radio-controlled airplanes. The idea was to encode (multiplex) multiple functions into a single channel, then decode the functions into real channels again in the airplane.

The project evolved to also add regular channels, support 16 channels, generate sound or an analog voltage, bootloader, encode PWM to PPM, decode PPM to PWM, custom splicing and advanced mixing of channels and so on. After seven revisions of the hardware, I’ve finally managed to send the board for automated assembling. The finished boards have now arrived. And they work!

Although I still need to do some manual work with each board, this makes the assembly much faster and I can start to sell more of the boards. The firmware is quite advanced so the device deserves a wider audience!

I’ve added a dedicated product page for Channel Wizard. There’s a thread on RCGroups about it.

Book: The Lean Startup

I’m halfway through the book The Lean Startup by IT entrepreneur Eric Ries. He applies the popular “Lean” concept to the discipline of starting and growing a company, something that peaks my own interest.

The idea is to avoid wasting effort on misdirected ideas by making reality checks early and often. A perfectly created product is still worthless if it turns out no-one wants such a product. Almost worthless — you have now gained valuable information about the market and that is in fact the goal of the start-up enterprise. But that wisdom could have been won cheaper than through a full development cycle and a wasted product.

Go check the real reviews, the web site or the book itself for more information.

Just a few taglines that stuck with me so far; Every start-up has a number of leaps of faith. Assumptions are best tested by “go and see for yourself”. This might be very easy with some ingenuity! Validated learning is the goal of a start-up. The relevant metric of the endurance of a start-up is not time or money, but the number of strategy pivots the start-up still has room for.

Bluetooth adapter teardown

Researching Bluetooth modules, it’s evident how darn expensive they are. $30 and up, usually. This is for small quantities but the regular stores don’t give a reasonable price even for larger quantities. I did find the aptly named Wireless Bluetooth RS232 TTL Transciever Module at DealExtreme for $6.60 (free shipping, of course). I haven’t got around to evaluate it yet.

But I also noticed these mini Bluetooth USB adapters for ridiculously low prices. DealExtreme has one for $1.80. I got two from eBay for $3.50 plus shipping. How can a retail product sell for so low compared to the main component inside??

Anyway. The dongle was easy to pry apart. It contains a bunch of 0402 passives, a BT chip, probably a USB interface chip and a SOT23 voltage regulator. On the top side, a single LED and through-hole 16MHz(?) crystal. Then I realized I wasn’t the first to take one apart:

Then again, the dongle I got uses an entirely different circuit…

On private projects

Today I stumbled across the animation short “The Passenger” on YouTube. An Australian animator spent eight years of his life and all of his private savings to complete the project. He described the process on his site. It’s an interesting read of a man who pursues his creative vision, determined to do it all himself and never compromise. I can identify with the strive to realize ideas , but it’s also a lesson to keep the scope within the manageable. With electronic devices, time to market can also be essential. As he points out:

“During the making of this film, A Star Wars trilogy, a Lord Of The Rings trilogy and a Harry Potter trilogy were made (not by me).”

Another project with undefined time schedule that comes to mind is Duke Nukem Forever

After one week

How’s the first full-time working week been?

I’ve enjoyed it and small tasks that I haven’t got around to fix for months are slowly being resolved. I’m learning more about different components and the industry. On the other hand:

  • Time spent on circuit board CAD: zero
  • Time spent on programming: zero

In spite of this, I’ve been occupied pretty much the whole time. Getting bored from oceans of free time seems remote. Actually I’m almost as stressed over all things planned as before. Staying occupied is easy; but is the time well spent? That’s something I’ve started to ask myself.


Måndag 16 april: På besök hos elektronikmontering Heltia i Linghem. Mycket intressant att se hur de jobbar och vad man bör tänka på vid elektronikkonstruktion. Om kortet är svårt att montera kan hela produkten bli omöjlig att sälja.