Send data between LEGO hubs and Raspberry Pi Pico

[KWSmit]

Pybricks uses Bluetooth BLE data broadcasting for sending information between LEGO hubs. The same technique can be used to send data between LEGO hubs and Raspberry Pi Pico. The good news is that it's not that difficult, thanks to Pybricks. I made a tutorial on Github. This way you can use a lot more sensors in your Pybricks projects. I'm thinking of using rfid-tags to distinguish which train enters the station 😄 Any other ideas?

[jaguilar]

Something along the lines of your plan to use the RFID tag to determine the position of a train is on my docket of things to do as well. It might be interesting to set the Pico up to command the Lego Hub via UART (or vice versa) so you only have to write the control program on one of the two devices, and the other one can be a simple listener program that never needs to change. Personally, I would run the control program on the Pico, since I'm getting into the C/C++-on-MCUs game.

[KWSmit]

That is something I have in my mind as well. Run a basic program on the train-hubs and the hubs that control switches and command them via UART. But I was thinking of controlling them from my PC. This gives you a lot of flexibility to change the track-layout or add trains.

[laurensvalk]

@Novakasa has entered the chat 😄 See also

• https://www.youtube.com/watch?v=UZj41oFs1KA
• https://github.com/Novakasa/brickrail

[jaguilar]

Hah, amazing. That's a beautiful looking program too. I doubt I would have the patience to make such a nice UI!

[laurensvalk]

This looks great, thanks for sharing @KWSmit !

[JorgePe]

Thanks for sharing this.
I was searching for a quick and cheap solution to integrate a LEGO hub with my new OpenHAB installation and now I have a Raspberry Pi Pico W as a mqtt2pybricks gateway. For now just a proof of concept - created a "Generic MQTT Thing" on the OpenHAB dashboard with one switch channel, defined a topic and the payloads to the ON and OFF commands and now I can turn a LEGO motor ON or OFF and integrate this "thing" with my other house "things" (so I can make a LEGO robot act according to the humidity level of a room or the status of a window...)

[KWSmit]

@JorgePe Sounds cool 😄 . Will there be a video of this?

[JorgePe]

Will be. When I get something better than just a motor. And also when I get my Pico gateway stable, it crashes after just 2 hours of working, not good for a domotic system.

[JorgePe]

OK, not production-grade but I think it serves as a demo: a fingerbot to control my bathroom lights ON/OFF.

The bathroom fan has no independent control so I have to turn the lights ON to circulate the air and control humidity. We moved to a reconditioned house one year ago and we're facing some humidity problems (it seems to be a general problem in this neighborhood). So I got some dehumidifiers and some humidity sensors and integrated everything with OpenHAB so I can turn them all ON with a time schedule or with a humidity threshold.

Next I will insert this fingerbot on the same rules of the dehumidifiers.

The Pico is in the room at front. I had it in another room (~10 meter) and sometimes the hub didn't receive the broadcast command.

I'm using the hub with batteries. If this gets approved by The Wife will make a power supply but for now the idea is to mount the fingerbot on the wall just when needed.

A link to the video: https://youtu.be/EwQePDEx5PI

And 2 lousy pictures:

[KWSmit]

Cool project solving real life issues 😀

[JorgePe]

Thanks.

I already had a "switch-bot bot":

it's great to control appliances that have a digital power button (one of my dehumidifiers) where you cannot leave it just permanently "ON" and control from a smart power plug. But not so great for two-state switches like this one. It is also BLE but i found some python examples and made my own gateway (with a Pi Zero W) so I found myself thinking that this was perfectably doable with LEGO. Not so cheap, not so discreete and definitely not so autonomous but I already had all I needed so why not?

Another reason was that I learned MQTT a few years ago with the MINDSTORMS EV3. Linux scripting, python, mqtt and BLE... I learned it all with LEGO :D

[laurensvalk]

There is now also this library to further simplify it, and use it with (almost) the same API as on the hubs. This has been an unfinished work for the longest time, so I figured it was finally time to update and publish it 😄

[JorgePe]

That's great!... but it is still micropython's exclusive.

To the moment I haven't found a way to have micropython with bluetooth working on RaspberryPi or my Ubuntu laptop. Also never found a pure python library that I could use ('bleak' seems to be client only, found David recommendation to use 'bless' somewhere but it seems also too complex for just advertising data) so this weekend I found a way to do it from command line with just 3 'hcittool' commands.

So importing 'subprocess' and making system calls to 'hcitool' I finally managed to use my Raspberry Pi Zero 2W to send "1" or "0" to the Hubs.

A little more expensive than the Raspberry Pi Pico W but much more stable, my mqtt2pybricks gateway has been running flawless for the last 48 hours.

Unfortunately I read somewhere that 'hcitool' is or is going to be deprecated.

[laurensvalk]

That's great!... but it is still micropython's exclusive.

Yeah, that's been one of the requests (e.g. interface with Arduino). Since you can get a board for $10, that's another way to do it.

We could perhaps do another version with Python. I don't know that all computers can generally advertise, but Raspberry Pi probably can.

For those where this isn't possible, an actual connection may be better, or use a MicroPython board with your computer as above.

[fkleon]

@laurensvalk Thanks for publishing that library, looking great!

I found myself in need of a Python implementation too, for debugging purposes and to simulate multiple hubs communicating with each other. So I've been been working on a pure Python, BlueZ-based implementation of the Pybricks BLE broadcast/observe protocol for a while now.

It's been slow going due to time constraints - and a lot of reading about DBus/BlueZ/BLE was required - however I finally managed to clean it up and publish it: https://github.com/fkleon/pybricks-ble

Eventually I'm wanting to offer the same API as on the hubs as well, but for now the observer and broadcaster implementations are separated.

@JorgePe I think this should run on a Raspberry Pi with Ubuntu. You're welcome to give it a try. The observer is implemented via bleak under the hood. For the broadcaster I did look into bless but as you say it's way too complex for simple BLE advertisements, so I implemented this on top of dbus_fast (which is what bleak/bless are using under the hood).

[laurensvalk]

Looks great @fkleon - thanks for sharing!

[JorgePe]

@fkleon Thanks!
I just installed it on a Raspberry Pi Zero 1W with Raspbian OS and used

python pb_broadcast --timeout 1 1 1

to send "1" through channel "1" to my LEGO fingerbot and it worked (the timeout was needed to prevent my robot to react several times).

I just had problems with the 'make format', it kept failing while trying to install 'hidapi'. since I don't understand 'make' and python virtual environments I just forced installation with

pip install -e '.' --break-system-packages

(not nice but this is just a test)

I guess I need to check the BlueZ DBus API if I want to mix Pi's and LEGO.