Background
One of the main aspects of our project is the satellite transmission capability which allows Helmet 127 to contact first responders from remote areas in the event of a serious impact. To this end, the STINGR module from Globalstar was chosen which also provides additional GPS functionality to obtain the user’s location as well. Through the generosity of Globalstar, our group received several STINGR units to use for our project. We designed a PCB to house the STINGR and breakout the necessary communication pins in order to facilitate communication with an MCU. This PCB design in Altium and the assembled PCB are shown below.
Update
In order to issue commands to the STINGR, a Nucelo development board is used for initial prototyping with the aim of using the MCU on the development kit in our final custom PCB. The mbed-os development environment is leveraged for the firmware to obtain access to common libraries and abstract the low level hardware interface.
The STINGR uses a standard UART interface, so mbed’s BufferedSerial class is used as the primary gateway of communication. A Stingr class is created to take advantage of object-oriented programming capabilities provided by C++. A code snippet is provided below showing the pins used in the Stingr class object created.
Using the STINGR manual, support for all the relevant STINGR commands are added. Some examples of issuing some simple commands including querying the firmware version of the STINGR, querying the transmission parameters and querying the STINGR status are shown below.
The more important testing sequence is related to sending a satellite transmission and confirming it was received. Globalstar configures each STINGR unit to forward transmission data to an email of choice in xml format. The transmission sequence is summarised below.
The STINGR unit was placed near a window to mimic outdoor operation and a test payload of user defined data was sent as seen in the below image.
The test message was successfully received via email and the same payload data of 0xBB, 0xCC, 0xDD and 0xFF can be seen in the payload section.
A demonstration of this process is available in the video gallery.
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