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High altitude balloon electronics

I'm part of a students association and we've had a helium tank in our place since 2003 which is still almost full. None of the current members knew where it came from until recently (turned out that we had a RC blimp of some sort back in those days...). So some time ago a member proposed that we could spend it in a high altitude balloon. Being electronics enthusiasts we thought about building our own electronics for the payload, trying to fit as much as possible in as few grams as possible. For now it's planned that the probe will have an APRS tracker, an emergency 433MHz tracker, a GPS module of course, a GSM module for sending a SMS with the landing position if network is available, a board with lots of sensors (temperatures, atmospheric pressure, light intensity, gamma/cosmic radiation, 3D acc+gyro+mag, humidity and probably wind speed (we're still not sure if that would be possible with a cheap, lightweight sensor). The whole thing will be controlled by a PIC32 and powered by 3xAA Lithium energizer batteries which are safer than lipos and tolerate very well low temperatures. It will log all its data into a microSD card. The electronics are composed by a mainboard with the PIC32 and some power supply stuff and 5 main verical modules that attach to the mainboard creating some sort of pentagonal prism which will be stuffed with thermal insulating material(a design that looks like the new mac pro's, but we thought it earlier). We've tried not to reinvent the wheel and we've adapted some designs from other people to our shape constraints.

Those 5 modules are:
-GSM module using a SIM900 GSM module and a power supply based on a TPS63020. This is our design.
-GPS module based on a SIM18 module, also our design. It'll use a passive patch antenna.
-APRS tracker which is just a stand-alone trackuino adapted to our design: http://www.trackuino.org/
-Sensors board which we are currently designing.
-Mission support board which will have power mosfets for the rope-cutting mechanism, heaters and some other stuff that's still to be defined.

Apart from those there's also a low power emergency 433MHz tracker which gets powered by two CR2032 batteries. In the event of a main power malfunction this tracker will power and take control of the GPS module to keep sending tracking data. We also designed the radiation sensor as a separate board because it'll be positioned in a different place.It is based on a design from elektor. I can't post the article's PDF because of possible copyright issues.

We'll also carry a mobius action camera inside to record the flight. We already have the balloons, the rope, the camera, the required antennas, legal information about the required permissions, some of the firmware and most of the electronics designed. We also have people with the required APRS receivers and radio licenses. The GPS and GSM modules are built and tested OK, soon we'll assemble the mainboard, the trackers and the radiation sensor.

Here's everything we've designed for now. There are separate files for the mainboard and the GSM module but everything else is fitted into a "panelized" PCB to save costs, I don't have the individual design files for each sub-board. The schematics may be a bit "dirty" and some values can be wrong or would need tweaking. I'll post final design files when everything is done.

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The antenna connections are designed so you can either stuff a U.FL connector or to bypass it with a 0ohm resistor and stuff a SMA edge mount connector. The GPS has a footprint for either a U.FL or a sarantel SL1206 helix antenna that we have from a previous project, but we'll use a passive ceramic patch antenna in this case, mounted on the top of the probe and brought to the module via thin coax terminated in a U.FL. The groundplane and mounting features for the patch are also included in the panelized PCB. Here's a picture of the GSM module which I've been testing these days:

Re: High altitude balloon electronics

Reply #1
Hi!

That's a nice project.

From my experience, if you plan to make temperature and light measurements, the sensors shall be placed outside the insulated nacelle at the end of a rod a few tens of cm away. If you let the sensors near to the nacelle's surface your measurements will be very disturbed by the thermal effects and the light reflecting on the nacelle.

Also, don't forget to get a radar reflector to make your system detectable by airplanes...

++
Gael