How to Track

Android Tracker Apps

The primary system used by the Casa de Balloon club to track our balloons is a modified Android phone running our own Casa de Balloon Tracker Android App.

This app will periodically take both photos and SMS GPS coordinates, and it will send Google maps links back to our personal phone on the ground.

Check out our blog post on making our tracker app to learn how we built it and what makes it different from most standard tracking apps available on the Android Market. A couple of the key differences include:

• We acquire a PARTIAL_WAKE_LOCK on tracking start to prevent the phone from ever going to sleep — battery life is not a concern, and at higher altitude, the higher heat from higher power consumption is a bonus.
• We have an intervalometer that periodically takes geotagged photos from the main camera.
• We log the raw GPS NMEA data to a file for post-flight analysis.
• We upload the GPS coordinates to our own web-based balloon tracking server powered by data.sparkfun.com.

In addition to our app, we both enable the Android Device Manager "Find My Phone" feature and install a backup app (Where's My Droid). On one of our earlier launches, the main tracker app malfunctioned, and Android Device Manager came to the rescue and let us recover the payload!

Hardware

Battery modification

On the hardware front, we start with a stock Android 4.0+ phone and then make the following changes:

• Rooting, which allows the tracker app to reboot the phone if necessary
• Replacing the LiPo battery with leads out to a 3xAA battery holder, which will be powered by three Energizer Ultimate AA Lithium batteries
• Hacking the GPS firmware to support tracking above 60K feet

Most Android devices should work, but we recommend the ZTE Z998 because it's cheap, fast, and GSM-compatible, and it comes with a decent camera and removable battery.

Special note about batteries: three AA lithium batteries output a total of 5.4V to 4.2V, with most of their operating life in the 4.8V range. This is higher than a typical LiPo battery (4.2V down to 3V), but most phones will be okay with that.

Some Android devices (most notably the Nexus S) implement overvoltage protection as part of their boot process and thus will refuse to boot on three fresh AA ultimate lithium batteries. You can either lightly discharge the pack to 80% capacity or wire in a parallel battery pack harness, boot off an old set of batteries, and then swap in brand new batteries after boot is complete.

Service Providers

We prefer to use AT&T-based MVNOs because the AT&T network is compatible with GSM phones and offers excellent coverage in rural areas.

AT&T Coverage Map of the Central Valley

Our preferred MVNO is Red Pocket Mobile and their GSMA service which is backed by AT&T. Our preferred plan is the "7-Day Unlimited" plan for $12.99 — it includes unlimited SMS and 50MB of data (which is more than enough for a launch).

This specific plan is not advertised by AT&T. To find it, activate a new SIM card and choose the "Unlimited" card type. When it prompts you to refill your card, look for an option to "see all plans" and that is where you should find the "7-Day Unlimited" plan.

433MHz Radio Tracking

In addition to the Android-based tracking system, we have been experimenting with 433MHz radio trackers based on OpenLRS hardware.

These OpenLRS modules consist of an Arduino mated to a 433MHz radio, which can be controlled via the Arduino RF22 library.

Here is the arduino code we loaded onto the OpenLRS hardware for the balloon and ground station.

Our balloon-side radio tracker includes:

• 433MHz 1W OpenLRS transmitter module with case removed
• 433MHz dipole antenna
• 3xAA battery holder for power
• uBlox MAX7 GPS with helical antenna
• OpenLog serial SD logger and 8GB microSDHC card to log raw GPS data

Radio Transmitter

A special note about uBlox GPS receivers — most of them are capable of tracking above 60K feet, but only if you explicitly place them in the "6 Airborne with <2g Acceleration" dynamic platform model. You can change this setting using uCenter and following directions like this (but remember — you want the "Airborne <2g Acceleration" model, not the pedestrian model). 

Our ground-side radio tracker includes:

• 433MHz OpenLRS receiver module
• 433MHz directional Yagi antenna
• SMA Male to N Male RF adapter to connect antenna to receiver

Radio Receiver

Legally operating these radios at their rated power levels requires an Amateur Radio License in the US. Getting one of those is surprisingly easy — contact your local chapter of the ARRL for more info.