Using Astrocast Astronode S+ with Teensy Microcontroller

The Astrocast Arduino library can be found here:

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

The library provides functions to interact with the Astronode device. Most of the functions return an integer which is interpreted as an enumerated type.

A good response is 24834, meaning ANS_STATUS_SUCCESS.

When using the Astrocast Arduino library with the Teensyduino library, many of the responses are  24835 ANS_STATUS_TIMEOUT, or 1 ANS_STATUS_CRC_NOT_VALID.

Extensive testing was performed using software debugging, an oscilloscope, a logic analyzer and continual comparison with other Arduino compatible devices that did not yield communications errors.

It took a long time to find the actual problem.

The Astrocast Arduino library makes use of the function:

size_t Stream::readBytesUntil(char terminator, char *buffer, size_t length)

This function terminates if:

• "length" characters have been read,
• timeout, or
• terminator character  detected.

The Astrocast library calls this function with a precisely calculated length, but expects to return on finding the terminator character.

Unfortunately, the implementation of this function differs between the Teensyduino library and other Arduino libraries, with the primary functional difference being the handling of the length parameter.

Teensyduino: readBytesUntil

The Teensyduino implementation decrements the length parameter before using it in the "while" loop test.

Arduino: readBytesUntil

The Arduino implementation uses the length parameter without modification.

The Astrocast Arduino library passes in a precisely calculated length parameter, even though it expects it to terminate based on finding the terminator ETX (03).

When used with the Teensyduino library the function terminates due to length and does not find the terminator character, so the result is considered invalid.

Then the next call to the function immediately finds the terminator character and returns; so the next result is considered invalid also.

The solution is simple once understood.

The Astrocast library does not need to pass in the precisely calculated length parameter, so the simplest solution is to increment the length parameter before passing it in, and then it works with both the standard Arduino libraries and the Teensyduino library.

 

Code snippet from Astronode.cpp - unmodified.

Code snippet of modified Astronode.cpp 

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.