Posted 2 January, 2021.
The Green Envy container has been unloaded from Wallenius Tugela ship and is now sitting in the port of Melbourne, waiting for customs clearance and bio security inspection. We know it is there because the container has a built-in satellite-based tracker that we designed ourselves. The tracker has been quiet for 10 days when the container was at sea, because the container was inside the ship’s hull and no signal could get out, but this morning we finally received a message.
The tracker itself was an interesting project. I happened to read about an autonomous boat in Make Magazine years ago (https://makezine.com/2016/08/22/solar-powered-autonomous-boat/) and it mentioned a “satellite modem” that could send short text messages through the Iridium satellite network. I thought that was really cool and I decided to buy one. It was a bit pricey at a couple of hundred dollars, but each message only cost a few cents, and the line rental is only about $20 per month (you only pay for the months you want to use it, there is no annual fee). If you want to build your own tracker, this is the modem: https://www.rock7.com/products/rockblock-iridium-9602-satellite-modem. The first version of our tracker wasn’t programmed well enough, and would run out of battery in a few days if it didn’t get a satellite fix. It would continue trying to send a message, which takes a lot of power. Green Envy team member Tom helped us re-write the code. Now it tries to send every ~7 hours, and if it can’t get in contact with the satellite network, it will just go back to sleep. That way the battery will last for months.
The sensors on the outside of the tracker box (visible in the photo) measures temperature and humidity in the container, and reports that in the message as well. This morning, the temperature in the container 24 degrees C and the relative humidity is 46 %. 
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// Eva
