For a research project we are using Hexiwear to measure the effectiveness of teaching and learning. The Hexiwear is used as a networking sensor device in that project. For that project we needed a docking station with wireless capabilities:
MicroelEctronica provides a docking station (see “Hexiwear: Teardown of the Hackable ‘Do-Anything’ Device“), but that docking station is too large for our needs.
The picture below shows the original docking station on the left, and the new and smaller one on the right:
The small docking station on the right has been designed and produced by Patrick Rossacher in a student project.
We do not need all these extra Click module slots, and the onboard OpenSDA circuit is not required. Instead a much smaller docking station has been created for charging and with added nRF24L01+ wireless connectivity: the nRF24L01+ is not closed source as the KW40 BLE stack: the Nordic stack open source and freely available, compiles with open source tools and do not requiere proprietary and expensive IAR tools.
- Charging through USB with the option to add a LiPo battery
- Charging LED
- K64F UART connection through the SWD header
- SWD connector to debug both the K64F and KW40 microcontroller of the Hexiwear
- Reset push buttons for KW40 and K64F
- Added Nordic Semiconductor nRF24L01+ 2.4 GHz transceiver
- Mounting holes
- Pass-through Hexiwear connector for custom extensions
- Breakout of signals for extensions
For the first prototype a PCB has been manufactured internally:
For the enclosure a 3D model has been created:
The docking station is a first prototype only and works fine. For the next design iteration we can remove the footprint of the 2×5 pins for the nRF external module which was a fallback solution. Additionally we want to change the placement of the the PCB antenna as in the current layout it is not placed in an ideal way.
The docking station has about the same height as the Hexiwear:
The original Hexiwear firmware is using the already outdated Kinetis SDK V1.3. So I have started a new firmware development based on the SDK V2.0 and Processor Expert. You can find it evolving on GitHub: https://github.com/ErichStyger/Hexiwear_v2
I’m considering to 3D print the Hexiwear enclosure for an even better integration. But for now the current solution looks good. Ready for the next round of design :-).
Happy Docking 🙂
- Project on GitHub: https://github.com/ErichStyger/Hexiwear_v2
- Hexiwear tear-down: Hexiwear: Teardown of the Hackable ‘Do-Anything’ Device
- Hexiwear web site: http://www.hexiwear.com/
This is awesome!
How did you design the pcb antenna?
Thank you for sharing.
There are PCB antenna design rules provided by Nordic Semiconductor (and others): it is a very simple lambda/4 antenna. We used another project as base (see https://mcuoneclipse.com/2015/05/20/tinyk20-usb-thumb-drive-enclosure/) and have an inhouse 3D antenna measurement system we can use.
So you have made a new PCB so you can change Bluetooth chip? This reminded me of an interesting webinar I heard, on app development for the Hexiwear using the Evothings platform. Their platform approach seemed interesting and should work regardless of the Bluetooth chip. I have not yet had the time to try it. It should appeal to you as it seems open. I wonder what experience and advice you have on development for the Central and Cloud sides of Bluetooth applications?
Regards – Charles
it does not ‘change’ the BLE chip (KW40), but it adds another wireless communication channel. The problem I have with the BLE stack on the KW40 is that it requires IAR tools to build that stack, and that the sources are not open. With the nRF24L01+ on that extension board I have a fully open source wireless connectivity stack. For the central/gateway we are going to use a Raspberry Pi with OpenHAB on it.
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Yeah, You gotta love opensource, I am interested in the KW40, I ordered some KITs from Digikey, I should have checked with the tools first although it was a quick last minute add to the order. So I definately have to buy IAR tools to build BLE firmware with it? Thats sad.
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Very nice work!
Is the PCB a commercial project or you could share the design.