Thursday, June 27, 2019

The Smallest Digipeater: New PicoAPRS Trick

Lately it seems balloons are everywhere in and around the Hudson Valley of New York. The Empire State Hot Air Balloon Festival has just concluded this past weekend,  this upcoming weekend is the anticipated "Reach For Near Space" balloon launch and middle of next month is the Hudson Valley Balloon Festival taking place again at the Dutchess County Fair Grounds.

Earlier still, this past April was yet another successful high altitude balloon launch by the United States Military Academy Astronomy Club which reached an altitude just over 100,000 feet and only traveled about 100 miles away in the process.

Path of the 2019 USMA BalloonSat. Altitude reached was just over
100,000 feet and landed more than 100 miles from launch point

Both the USMA Cadets and the Reach For Near Space team led by Gary KD2PYB use APRS to track the weather balloons.  Last summer, Steve K2GOG also used APRS to track his much, much lower elevation manned balloon flight.

APRS Transmitters for Balloon Tracking

There are many easily obtainable VHF 2m amateur radio APRS "transmitters" to be considered for balloon tracking, but there is one that has recently added a new trick to its list of features and its the PicoAPRS.

The popular Sainsonic AVRT5, Byonics MicroTrak 2001, TrackSoar V2, StratoTrack, and BigRedBee are all relatively low cost, low weight options but PicoAPRS and PicoAPRS Lite offer a few unique things not found always found in the other products mentioned that may appeal to those interested in high altitude device tracking.

PicoAPRS v2 & v3

The latest PicoAPRS is 37% smaller than the original v2.  Version 3 is only 44 grams including battery.  The PicoAPRS Lite which is designed for balloon enthusiasts is only 7 grams, without battery and antenna. Both versions contain a receiver to provide a fully functioning APRS tracker as well as a display and simple 3 button interface for configuration.

PicoAPRS Lite does not have a display and must be provisioned by computer.  The engineer behind the PicoAPRS products, Taner DB1NTO, has created near identical firmware for all three versions and now includes the ability to "digipeat" APRS packets which may be very useful for those looking for a tracker and a payload to be monitored from the ground. The PicoAPRS Lite unfortunately at this time does not support the digipeat function.

Temperature and barometric pressure sensors are built into the PicoAPRS Lite too which makes its APRS data capable of sharing more than just its GPS location.

Roughly costing $159 USD, the PicoAPRS may be a higher quality option compared to the Sainsonic AVRT5 which is $40-50 USD less but at a far higher considerable weight.

The "Digipeater" Firmware for PicoAPRS

Because the PicoAPRS products are designed around the ATmega 1284p micro-controller,  there is a lot of flexibility for future upgrades and features. The entire revision log can be found here for the older, current and latest PicoAPRS products

After I upgraded my V2 PicoAPRS to firmware version v014, it was easy to go from tracker mode to digipeater mode by simply toggling to the appropriate menu.

Perhaps a balloon borne, solar or battery powered PicoAPRS digipeater would be a fun project this summer.  Maybe in the future the PicoAPRS Lite will support the ability to digipeat or the PicoAPRS v3 to support some form of telemetry like temperature and air pressure.

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