mb2-external-serial

Bart Massey 2023

This is the serial-hal-blocking-echo example from the microbit crate. It has been modified to be MicroBit V2 only, to build and run a bit more easily, and to work with external serial hardware rather than the debug serial interface.

Hardware Setup

I set this up using the MicroBit V2, the AdaFruit DragonTail to get the pins out conveniently, a third-party TTL Serial Adapter that came with the necessary cable, and a USB hub.

• Start with everything powered off and disconnected (of course).

• Plug the DragonTail onto the edge card connector of the MB2 oriented so that the pins on the back of the DragonTail are also on the back of the MB2. (Do not get this upside down.)

• Plug a wire onto the GND pin of the Serial Adapter. Plug the other end of that wire into a pin marked "-" on the DragonTail. I recommend the pin next to Pin 0 on the DragonTail, as it will make the next steps slightly easier.

• Plug a wire onto the RX pin of the Serial Adapter; plug the other end of that wire into Pin 0 on the DragonTail. Note that the DragonTail pins are labeled on the opposite side of the board (to avoid marring the art, I think; thanks AdaFruit). Be careful about which is which.

• Plug a wire onto the TX pin of the Serial Adapter; plug the other end of that wire into Pin 1 on the DragonTail.

• Plug both the Serial Adapter and the MB2 into USB. I strongly recommend buying a USB Hub with switches and plugging both boards into the same hub while the switches are turned off.

  • A USB Hub may possibly help protect your valuable laptop or desktop from damage; if you want to double down on safety, you can buy a USB Isolator to put between the hub and the computer.

  • Plugging both devices into the same hub will help ensure that they share a common ground, which should not be necessary, but hey.

  • Plugging in switched off makes it easier to play with the devices and only turn them on when needed.

My setup looks like this:

Operation

I will document Linux, since that is what I used. Windows or Mac users are on their own, but the steps should be similar.

• Make sure cargo-embed is installed (say cargo install cargo-embed if needed).

• Turn on (or plug in) the MB2 and the Serial Adapter.

• Make sure Minicom is installed (see your distro; on Debian say apt-get install minicom). Open a new terminal and s ay minicom -D /dev/ttyUSB0 (hopefully; you might conceivably have a different TTY) to connect to the serial adapter. The default Minicom settings of 115200/8/N/1 are what are desired here.

• Say cargo embed --release.

You should see this code built, uploaded, and your Minicom terminal window should print "Hello World:". Subsequent typing of keys in the terminal window should result in their being echoed back.

License and Acknowledgments

All the good stuff was in the original example. Thanks to the authors. Like the original example, this work is made available under the "BSD-0 License": see the file LICENSE.txt in this distribution for license terms.