SparkFun Forums

[integ3r]

Good evening SFE Forums!

I am a junior at Regis Jesuit High School in lovely Aurora, Colorado (warning: external link). After reading the post about Nate's high altitude balloon, I decided to look at other extremely well-done projects like HALO, NSTAR, ARHAB, and more. After distilling a lot of the information I found (as if Nate's article wasn't already informative enough) I decided to introduce the idea of launching a balloon to my high school's tech club.

The tech club has been struggling financially for the past couple years due to a less-than-spectacular budget from the school administration (think <$100 per year). However, after introducing the project, we have been backed by the physics department, photography club, aerospace club, parent's club, library, and other school organizations who are willing to pitch in a LOT of support (total of more than $900, potentially).

We have researched many of the parts available to us through SparkFun and other sources and have come up with the following partlist:

Core: Atmel ATxmega128A1 AVR (lots of IOs so it's definitely expandable, low power)

Sensors:

• ADXL345 Accelerometer
• InvenSense ITG-3200 Gyro
• Honeywell HMC6343 Magneto
• TI TMP102 Digital Temp Sensor
• Sensirion SHT21 or SHT18 Humidity Sensor (SHT18 has a really weird I2C protocol)
• TAOS TSL230R Light-To-Frequency Converter
• Honeywell HSCMAND1.6BGSA3 Pressure Sensor

Logging and Communication:

• Direct MicroSD card connection (and a FAT32 library) for filesystem access
• 2x Digi XTend 900 1W Digital Modem
• NS73M FM Radio Transmitter (we had a free SPI bus)
• Telit GM862-GPS Cellular/GPS Module

The reason for the substitution of the pressure sensor is that the BMP085 can only measure up to around 60,000 feet accurately. We wanted this data to be usable by the physics department in labs, studies, etc. The HSCMAND1.6BGSA3 has an acceptable pressure range and can measure up to a near vacuum without accuracy diminishing. Do we really need the gyro, though?

We also want this project to be modular so it can be used, re-used, and upgraded from school year to school year. Nate's very nice High Altitude Sensing board just won't work for our purposes because everything is soldered on there permanently. Sure, we could get a bunch of SparkFun's breakout boards if we needed. But are there any other suggestions (like designing our own PCBs)? How much would it cost if we had one PCB per sensor? Who would fabricate, silkscreen, and drill them if not us? What about soldering if we don't want to ruin expensive sensors through trial and error?

Thanks for the help. We are expecting this project to be awesome so some help and some more information would be appreciated!

[glassfog]

Posting in the forum is a good idea. May I suggest an email or a phone call to Customer Service? You might even consider asking to talk to Nate; see if you can interest him in helping.

Your post is a good starting point. Again, if I may, I suggest you be prepared to ask for specific and detail help when you contact them.

Keep us posted.

[cpolley]

Modular is a great idea, especially if you're using all this gear for the first time and might need to chop and change the setup as you learn.

The BatchPCB.com service is a good option for PCB fabrication - there are tutorials here on sparkfun that will walk you through the whole process.

If you're worried about soldering and you have a little extra cash available, breakout boards might be the way to go for the sensors (& especially that monster xmega). It cuts out most of the PCB fabrication and some of the hairier soldering work - so you don't get to learn those skills, but on the other hand it's much lower risk and allows you to focus on the main project.

Once you're ready to start working on the xmega, you can get a lot of help from the avrfreaks forum as well as here.

Good luck!