On the 29th August – 1st September, I joined over 1000 other campers at Electromagnetic Field camp in Milton Keynes. Said field was equipped with mains power and high speed internet, which allowed them to host some great workshops, talks and demos including on site laser cutting! I camped with a few other UKHAS members in our “villiage” aptly named “HABVille”

We ran a couple of launches, which had a pretty good turn out of interested people who arrived on time to watch. However with tradition the launches were vastly delayed as trackers were still being assembled and programmed.

The first of these was one of my Cheapo boards on a foil balloon, which sadly didn’t quite manage to enter a float, but did cross the channel. The second was a JOEY board running both Matt’s TurboHAB and RTTY, a UKHASnet node, and Richard’s Bristol University SEDS tracker. All 3 of these payloads were carefully strung under a 100g balloon and filled with all the helium we could get our hands on.

One of the other perks of the camp were the badges, which unfortunately weren’t quite ready to hand out as soon as the gates opened. The radio network for delivering weather and schedule updates (an awesome idea) was pretty ropey too. But provided some excitement when someones badge started working on it.

We also spent a bit of time down at The Grid, an interactive light installation put together by Adam Greig and David Turner. Which attracted a lot of attention when it sprung to life at night, with people drunkenly charging around in amazement as the poles lit up around them. Adam and David clearly put an awful lot of work into this project, which they discussed in their talk. I shot some footage on my unfortunately gimbal-less hex.

NottingHack brought along their BarBot, which happily served me an interesting concoction of alcohol.

The NavSpark was an indiegogo campaign launched some time last year. It is essentially a GPS receiver with a 100MHz  processor and 1024kb of flash memory. It also allows you to compile and upload code for it straight from the Arduino IDE. It comes in at a price of around 15 USD and a similar form factor to that of the Arduino Nano.

NavSpark board pinout.

After many months of waiting and a few badly translated Chinese update emails, my two preorder NavSpark boards arrived! They sat around on my desk for a fair few weeks before I decided to sit down and crack on with turning them into trackers.

The first step was to set one up on some breadboard with an NTX2B and a resistor network to set the shift, then toggle a GPIO pin on and off to produce the mark/space tones required for RTTY.

NavSpark board and NTX2B on breadboard

It took a bit of faffing around to actually get code onto it. Sometimes it will not allow you to upload, and you have to short BOOT_SEL to GND to restore the working bootloader from ROM, then try again. But I eventually had a program that was toggling pin 12 on and off.

Putting “GnssConf.init();” in “setup()” initializes the GNSS receiver and causes “task_called_after_GNSS_update()” to run. Inside this function its remarkably easy to get all the GPS data your tracker might want, without the need to mess around with any NMEA parsing.

void task_called_after_GNSS_update(void)
{
GnssInfo.update();
gps_hour = GnssInfo.time.hour();
gps_min = GnssInfo.time.minute();
gps_sec = GnssInfo.time.second();

lat = GnssInfo.location.latitude();
lng = GnssInfo.location.longitude();

alt = GnssInfo.altitude.meters();

gps_sats = GnssInfo.satellites.numGPSInUse(NULL);
gln_sats = GnssInfo.satellites.numGLNInUse(NULL);

}

Then came the challenge to tackle the timing of sending RTTY. Luckily it turns out the Navspark has a few timers to use with millisecond precision [page 80 TIMER]

uint8_t tmr0 = Timer0.every(20, tmr_task);

Its then as simple as sticking Anthony Stirk’s great little Interrupt based RTTY script inside the tmr_task() function. With some minimal modification to write the GPIO pin high/low.

Check out the code here.

I soldered a couple of 4k2 0603 resistors between VCC and DATA, then DATA and GND on the NTX2, also shorting VCC and EN. I then soldered a 47K and 10K resistor in series to the DATA pin, then connected the other end to our NavSpark’s GPIO pin. You can solder the NavSpark board pretty much straight on top of the NTX2B, but its probably a good idea to add some insulation (kapton tape) between the two. The NTX2 GND is connected to the GND on the board, and VCC to the 3.3v regulated output.

NTX2B with resistors.

NTX2B / NavSpark sandwich.

NavSpark side up, showing antenna.

NTX2B side up, showing antenna.

Sitting on my desk, still managed a time fix.

Overall I found the NavSpark hardware very easy to work with, and the coding perhaps even easier than a normal Arduino/uBlox.NTX2 tracker, mainly due to the lack of requirement for a NMEA parser. The NavSpark documentation is a little sparse and badly translated, however everything you need programming wise can be found here. The performance of the GPS in terms of time to first fix is very good, getting a time fix after the first sentence, and a position fix after 4/5 sentences. Once it had aquired a fix and with the NTX2B running, with the supply voltage set at 5.6V and fed to the battery input, the tracker was using about 65mA current.

Would I recommend the NavSpark over an AVR/uBlox based tracker?

I’d certainly consider it! There is probably far more information out there in the AVR world, but if you are just making a simple RTTY tracker then it is certainly a viable option. Just wait for the flight test in the next month or so before rushing out to launch one!

Speaking of flight, what about the COCOM GPS limit?

According to SkyTraq the GPS will only shutdown if 18km altitude AND 1000km/h velocity are exceed simultaneously, meaning it should well be suitable for HAB use.

Chris Stubbs M6EDF launched a High Altitude Balloon from the CARS club night at the Oaklands Museum on the 1st of July 2014. This page contains information on the flight of CARS1 for those interested in tracking the flight.

The flight started at 19:50BST on Tuesday.

• 19:50BST – Flight launched from Oaklands Museum, Chelmsford
• 23:05BST – The balloon has passed Maidstone, heading South, floating at 4,600 metres
• 00:00BST – The balloon left the East Sussex coast, floating over the English Channel towards France
• 02:50BST – This was the last packet received here in Southend, showing CARS1 halfway across the English Channel heading to France
• 06:45BST on Wednesday morning, the balloon was still in flight, over France at 5,400metres, but no packets have been received as of 0720BST. Voltage of the single 1.5 volt battery has dropped to 0.7V, so CARS1 may be flying but no longer be transmitting.

The Flightpath

To see where “CARS1″ is, go to http://spacenear.us/tracker/?filter=CARS1

The Frequency

As of 23:05 local, I’m tracking a very strong signal on 434.293MHz USB – Stations tracking at this time include G6GZH, G0TDJ, M0JCU, PB0AHX, G6SUQ, M6EDF, F5APQ, M0PSX, F1OIL, G4MYS, G7OGX, G8KNN-1, G8KNN, G8JZT, G0WXI, ASTRA_J, G0CXW_2, G8APZ

The last packet received here in Southend-on-Sea was at 0354BST, but it continued to be tracked by others beyond that point.

Chat with Chris

As of 23:00, Chris M6EDF is in the High Altitude chatroom: webchat.freenode.net/?channels=highaltitude – Just made contact to thank Chris for his talk and to confirm he’s very audible in Southend-on-Sea

CARS-1 Launch Video

A short video showing the launch and the tracking of this HAB flight:

CARS-1 Photos

Pictures of the launch and presentation 01 July 2014 at Oaklands Museum, for the Chelmsford Amateur Radio Society July Club Night…

For more on this, see CARS-1 High Altitude Balloon Video

Article by Pete M0PSX – http://www.essexham.co.uk/news/cars1-hab.html