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Drops N’ Roses – This is not over

Hey !

I know… I should not post because ROSE is over. But drops have evolved since the last orals. And I thought you may be interested in our progress.
First of all, some of you were really surprised when we announced one year autonomy for our drop with a cell battery. And in a way, you were right. Thanks to a tiny gecko circuit, I measured the consumption of one of our drop. A picture is worth a thousand words.

Tiny Gecko and drop

led_on

The three first picks you see are when our drop is sending advertising packets every 0.5 second. During advertising, our drop is idle. It means that our external flash is in ultradeep sleep mode, and so we have an average consumption of 65uA. Note that depending on advertising period, the consumption could be between 7uA (advertising every 10 seconds) and up to 1.13mA (every 20ms).

Then, the second range represents a connection period. Some peaks are bigger than others : it is when we read (or write) in our external flash. The average consumption when the drop is connected is around 190uA when we don’t access the external flash (but it is awake and ready).

The third range corresponds to a connection with our drop’s led on. At this moment, I indeed send a request to turn it on. When I saw how much it consumes (around 3mA), I was really happy that I turned it off a few days ago, and add a command if we really want to turn it on to identify to which drop we are connected. The led is turned off when I disconnect.

These information allow me to estimate our battery consumption. I was quite disappointed because it turns out to consume more than I expected (and calculated with the different datasheets I had). Especially for the memory. One access to the memory lasts 73ms when I was expecting 2ms… And because the consumption is around 5mA when we access to the flash… well… it is not so good.
But it is still good. We still can make 1000 connection per day, with 10 operations on the external memory, and advertise every 0.5 second and last one year. And I am thinking of other ways to improve our consumption. (If you have any idea, I am looking forward to suggestion!)

 

Hopefully, I have not only bad news ! I have also worked on DFU (thanks to Drix). We are now able to flash a program thanks to DFU and the use of BLE (and NRF application). So now, when I want to update one of my drop, I don’t need a JLink probe anymore. I can send a signed command to my drop thanks to our control application (dropscanner) to launch DFU. Then, the drop waits until it has a new software. As soon as the drop receives the new program, it is launched.

 

A lot of work is still left to do. With our teachers, we thought of a new API, that could be used with other BLE devices (not only drops). I also thought of many other improvments such as adding encryption for signed commands because we don’t want that a hacker listening to all our transactions could replay them, etc !

Thank you for your support during ROSE. It has been a great experience. So amazing!
See you (maybe) 🙂

1 comment to Drops N’ Roses – This is not over

  • Well, I only see good news here, you confirm the 1 year autonomy, even with 1000 connection per day (quite hard to reach), that’s amazing!
    Good job 😉