Stratospheric Balloon Experiment – A Start

I first encountered a Ham who launched a high altitude weather balloon in about 2006. At the time I was 10 years from getting my Amateur radio Technician’s license. Regardless, I saw the wisdom of using a radio to transmit location data (APRS) from a GPS to enable tracking of the balloon and your payload. I’ve been busy with work and family during the time in between then and now. Since then, things have slowed down a little. I’ve removed some of the chaos of my work by downsizing my career. Also, my kids are a lot older now leaving more time to experiment with things. Sometimes I feel like I’m 17 again :)Moving right along… This winter my two younger sons and I bumped into the UMaine High Altitude Ballooning group ( at the Maine Science Festival in Bangor, ME ( I talked with the professor who runs the program with a NASA grant. He even indicated that they work with homeschool kids (Win! We homeschool our kids.) That sparked my research into different experiments my kids could carry out and send up on a flight to the “edge of space.”I found lots of info online about it. There are lots of resources like Then, in the course of deciding how to involve my kids’ homeschool science with a HAB project I remembered we already had exactly what we needed! A “Sun and Sky Monitonring Station” from RadioShack based on Forest Mimms III’s work using LEDs as narrow-band photo diodes ( It’s really crazy, because my wife bought the old kit at a thrift store for $3.99 last year thinking it would come in handy. How right she was!

So, we spent a few weeks working through some of the basic atmospheric science presented in the book. Then, I got started building a prototype UV data logger based on a couple of RadioShack UV (405nm) LEDs. I started with the logger running on a PicAxe 08M chip. I encountered problems that I later found had NOTHING to do with the PicAxe. I was working my way to the bottom of my sporadic voltage reading issues where the numbers coming out of the ADC would randomly climb and then drop back to 0. I figured it was related to my poorly structured circuit and/or the very small number of electrons produced by the LEDs.

I switched to an Arduino but I still had the same issues — that didn’t surprise me. But it made me feel better. Then I was determined I needed to handle the very low ampere output of the LED better and wired it to a unity gain OpAmp circuit based on the one that Forest Mimms III presents in that Makezine article I referenced above. That worked like a charm! I extended it a little bit because I reason that, since the LEDs are so directional in their detection of light, that I’ll need at least four pointing outward spaced 90 degrees apart. My hope is that, if I average the values of all four LEDs we’ll be able to detect the trend in UV light intensity and factor out the angle of the LEDs with respect to the sun.

Here is a sneak peak at my very first prototype that seems to work:

This is an arduino with a custom op amp circuit to drive the Arduino's ADC circuits from the UV LEDs acting as UV sensors.
This is an arduino with a custom op amp circuit to drive the Arduino’s ADC circuits from the UV LEDs acting as UV sensors.

Here’s how it looked when I figured out how to put the circuits inside the the official UMaine provided enclosure:

Our UV Experiment packaged up in the official UMaine HAB enclosure
Our UV Experiment packaged up in the official UMaine HAB enclosure

I’ve got a few different pieces of code I’ve written for handling this datalogging and testing process. However, I’ll save that for another post.

And just in case you haven’t seen the Sun and Sky Monitoring Station:

Sun and Sky Monitoring Station - Vintage, by Forest Mimms from Radio Shack
Sun and Sky Monitoring Station