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diff --git a/README.md b/README.md new file mode 100644 index 0000000..93d7331 --- /dev/null +++ b/README.md @@ -0,0 +1,86 @@ +# NRF52 Dongle + +I'm using [OpenThread](https://openthread.io) to control my home automation +devices. They are built around a [nRF52840 +SoC](https://www.nordicsemi.com/products/nrf52840), provided by a [Holyiot +18010 module](http://www.holyiot.com/eacp_view.asp?id=278) with built-in +antenna. For the OpenThread gateway, I've been using the [nRF52840 +Dongle](https://www.nordicsemi.com/Products/Development-hardware/nrf52840-dongle) +from [Nordic Semiconductor](https://www.nordicsemi.com), running as a [Radio +Co-Processor (RCP)](https://openthread.io/platforms/co-processor). While it's +good for prototyping, I'm not completely happy with it for this purpose, as it +doesn't fit securely in a USB port, and has a weak antenna. + +That's why I decided to make my own nRF52840 based dongle, with an SMA +connector for an external antenna. + + +## Photos + +[](images/nrf52-dongle.jpeg) + +[](images/nrf52-dongle-enclosure.jpeg) + + +## Hardware + +Since I'm not experienced in designing RF PCBs, I decided to use an existing +module with a nRF52840 SoC. Searching on the internet, I found the [NINA-B301 +module](https://www.u-blox.com/en/product/nina-b30-series-open-cpu-0) from +[u-blox](https://www.u-blox.com), which is based on the nRF52840 SoC and has a +pin for the RF output that can be connected to an SMA connector. + +The board was designed using [KiCad](https://www.kicad.org/) 6.0. The +[schematic](images/schematic.png) is simple because most the work is done by +the NINA-B301 module, which includes both 32 MHz and 32.768 kHz crystals. In +addition there is an [ARM +SWD](https://developer.arm.com/documentation/ihi0031/a/The-Serial-Wire-Debug-Port--SW-DP-/Introduction-to-the-ARM-Serial-Wire-Debug--SWD--protocol) +connector for programming, a voltage regulator providing 3.3V from the 5V USB, +and a USB connector with the corresponding ESD protection and power filtering. + +I used the same pin for the LED as the green LED on the Nordic nRF52840 dongle +to be able to reuse the existing firmares. However, I chose not to include a +RGB LED or a reset switch. + +The PCB is a two-layer design and can fit into a [Hammond +1551USB2](https://www.hammfg.com/electronics/small-case/plastic/1551usb) +enclosure that I'm using as a standard. The RF trace between the NINA-B301 +module and the SMA connector is kept as short as possible, with 50 ohm +impedance matching making it wide given the 2-layer design. On the other hand, +I didn't used differential impedance matching for the USB traces. This isn't +really needed for full-speed devices and when the traces are kept short, and +it's pretty tough to do a 2-layer PCB. I just made sure the two traces were +the same length. + +All the components from the [bill of material](BOM.txt) should be easily +available from many distributors. Soldering of the NINA-B301 module requires a +hot air gun, but the LGA style pads are relatively large, so it's relatively +easy to do. I personally didn't use a stencil. + + +## Software + +I haven't developped any a custom software for this dongle. Instead, I am using +the [ot-nrf528xx](https://github.com/openthread/ot-nrf528xx) repository to +build an RCP firmware with a few commands: + +``` + ./script/build nrf52840 USB_trans + cd ./build/bin + arm-none-eabi-objcopy -O ihex ot-rcp ot-rcp.hex +``` + +Then the resulting HEX file can be flashed with: + +``` + pyocd flash -e chip -t nrf52 ot-rcp.hex +``` + +The nRF52840 SoC is quite powerful, so it can also be used as a Matter or BLE +dongle, or for other purposes as well. + + +## License + +The contents of this repository is released under the [Creative Commons +Attribution-ShareAlike 4.0 International License (CC BY-SA 4.0)](LICENSE). |