Satellite Communications with Voyager - Part 1

 Satellite Communications - Part 1

Its always been the plan to add Satellite Communications to Voyager to allow for telemetry and re-routing whilst at sea.

The decision has been made to use the Astronode S+ from Astrocast.

https://www.astrocast.com/products/astronode-s-plus/

Astronode S+

The Astronode device allows for small telemetry messages to be uploaded from the vessel every few hours and simple commands to be received.

It will operate from 3V3, with an average current draw of less than 1mA while waiting to transmit its messages.

The peak current while transmitting is around 80mA. These power requirements can easily be supported onboard Voyager.

A new controller for Voyager has been designed with the key changes being a change from the Teeny3.6 to Teensy4.1, as well as support for the additional serial connection to the Astronode S+ Sat Comms device.

Prototype Voyager Controller V4.0

Astrocast provide a software library for interacting with the Astronode S+ within the Arduino C++ environment.

Astrocast/astronode-arduino-library: Arduino library and example for the Astronode S (github.com)

I used the Astrocast Arduino Library to exercise the Astronode S+ device using various Arduino compatible devices. These mostly worked ok, but I was having problems with the Teensy devices.

This was a problem because the Teensy device was only one that had to work.

The Teensy devices should have been the most capable of the microcontrollers in use, but they continually returned errors when communicating with the Astronode S+ device using simple 9600Baud serial data.

It took several months of part-time testing and debugging in hardware and software to eventually track down the reason for the communication errors between the Teensy devices and the Astronode devices.

In short, it is due to the Teensy Arduino Stream library, within Teensyduino, having a slight difference in implementation to other Arduino Stream libraries. 
The difference is only highlighted in edge cases, and would rarely become apparent. The Teensyduino Stream library is around 5 years old, and has always had this specific characteristic.
The Astrocast Arduino Library makes use of the Stream library, but it exercises the edge case that highlights the difference between the Teensyduino and other Arduino libraries.

The precise details of the problem with the interaction between the  Astrocast Arduino library and the Teensyduino library are covered in the next post, along with the solution.