LEGO Powered Up Relay

I needed a way to turn a LEGO motor ON and OFF using a Powered Up hub but keeping power supplies independent. This way I can control a large current demanding motor without draining out the Hub batteries (and also without the need to use a custom cable).

So I used a Power Functions switch as a relay:

LEGO Powered Up relay

Also took the chance to try LDCad on linux. Not so easy to use as LEGO Digital Designer (I am a zero with CAD) but after a while I got a pretty close model. To create a PDF with the instructions I then used LPub3D – I couldn’t install the ‘.deb’ file because of missing dependencies no longer available for my Ubuntu laptop but found out that the ‘.AppImage’ works fine.

The instructions on this PDF file also have a list of the parts that I needed to get from LDView (LPub3D generates a nice image with all the parts but without describing those parts). I also couldn’t install the ‘.deb’ version so I used the ‘.exe’ for Windows, it runs fine with Wine.

The model uses a Powered Up / WeDo 2 motor but it can also use a Power Function M motor or a MINDSTORMS medium motor so this relay may use with different technologies (IR, Bluetooth, Wi-Fi, USB) as long as you just need an ON/OFF control of the motor.

Using a Power Functions LiPo battery you can still regulate the output power

A video of the relay working:

And another showing how I use it in my LEGO Imperial Conveyex Transport based on the old LEGO monorail system:

Big thanks to Roland Melkert, Trevor Sandy, Travis Cobbs who designed these great open source tools (and probably many others who contributed).

LEGO Wireless Protocol officially available

LEGO released the specs for the Powered Up BLE-based protocol (LWP):

Interestingly the document is also available as an open souce (MIT license) project at Github:

Is’s always a good sign when a big company like LEGO embraces open source so let’s hope for the best

Merry Christmas to all!

Smoke generator for LEGO Powered Up Train

This post is part 1 of 2 of  Gatto Negro

A few months ago I have made my own version of Holger Matthes’ BR80. It was not a full replica because I didn’t have all the pieces required so I had to improvise. I also opted for an all-black version instead of a black+red combination.

I decided I needed a steam engine after some experiments with a MINDSTORMS EV3 setup with a train turntable, two rail switches and a pseudo train with SBrick and RFID:

After I added a mechanism to disengage the train engine from the cargo wagon I decided I needed a steam engine since modern trains don’t need the turntable to operate.

As the SBrick had 4 outputs and I was only using 2 for the motor and the lights I wonder what else could I add to it. Choosed two extra functions that would look good on a LUG exhibition:

  • a smoke engine
  • a horn

The initial project was dismantled but I’m now returning to it with a MILS-based layout to use in larger dioramas with other PLUG fellows:

Currently the turntable and the rail switches are still manually operated but at least I now have a steam engine. With real smoke:

This is ‘Gatto Negro’. It means ‘Black Catt’, I’m using the extra ‘T’ because in Bluetooth Low Energy jargon ‘GATT’ means ‘General Attributes’ and I’ve been using a lot the linux command ‘gatttool’ to quickly test my BLE devices.

Of course ‘Gatto Negro’ is also BLE – it uses the new LEGO Powered Up hub and the PUP version of the LEGO Medium motor instead of the Power Functions IR Receiver, LiPo battery and M motor.

Unfortunately with the current firmware of the PUP Hub using a M motor isn’t the best option: the remote BLE Handset doesn’t hold the speed setting so we have to control the train with short or long button presses, always at full speed. Same happens with current LEGO App because LEGO programmers decided that only a train motor should be used for trains (each PUP device has an unique AutoID and the App was made to use train motors with train controls and non-train motors with car controls).

So I made my own ‘Gatto Negro’ aplication, with MIT AI2.

Next posts I’ll write about the smoke generator and the App.

The new LEGO Powered Up Remote Control

This post is part 1 of 2 of  LEGO Powered Up Remote Control

This week I got a question from Nathan Kunicki about using the BOOST Tacho Motor with the new Powered Up hub.

He already succeeded with the other WeDo 2 and BOOST devices so the motor was the last challenge. So I tried a few ideas but nothing.

I told him that probably the motor was not supported by the current firmware… and then he told me that when we use the new Remote it works (as if a WeDo 2 motor, just ON or OFF).

Well… my lovely wife just gave me this weekend my future birthday gift: the new LEGO Cargo Train. And it has a Powered Up remote so… let me try it.

No, we couldn’t find a way to control the motor. But I learned a bit about the Remote (thanks Nathan!) Enough to use it as a standalone BLE controller without the LEGO Powered Up “HUB NO.4″… it’s so easy that any BLE master can use it.

And, of course, the MINDSTORMS EV3 when running ev3dev:

to be continued…


Making an Android app for LEGO Powered Up – explanation

So how does this “App Inventor”-thing work?

To create an app for Android we just need a browser to access the online app creator tool. We have a Design view where we add our components like buttons and sliders and a Blocks view where we use the method blocks provided  by each component we added to our Design.

We can build our app and download an ‘apk’ file to install on our Android phone or tablet but that’s not practical while we are still testing some ideas and debugging the way our blocks work. So the best way is installing the MIT AI2 Companion App on our Android device so every action we make in the online tool is synchronized to it through USB or wi-fi.

App Inventor 2 provides a Palette with lots of usefull components but to use LEGO Powered Up we need to add an Extension that allows AI2 to talk with Bluetooth Low Energy devices. At the moment BluetoothLE is the only supported extension and I must say they have been doing a great work this last year (they even gave me access to a beta version a few months ago while fixing a bug I was dealing with) including writing a good explanation of all the blocks provided with some examples for Arduino and BBC micro:bit.

After importing the extension  we just drag it to the Viewer to get a ‘BluetoothLE1′ component at the bottom of the Viewer, on the “Non-visible components” area. Doesn’t seem much but if we change to Blocks view and look to this component we’ll see lots of blocks.

So let’s start creating our App!

We will use some BluetoothLE blocks to communicate with our LEGO “HUB NO.4” device. This blocks require a ServiceUUID and a CharUUID that we will store in global variables:

Currently the ServiceUUID and CharUUID are the same as LEGO BOOST hub but please note that there is no guarantee that future firmware releases will keep them allways equal.

We will also create a list of our devices:

Yes, a list of one device is silly but I have more devices like my BOOST Vernie and of course I’m planning to have a few more Powered Up devices in a near future so a list is usefull. You can call whatever you want to your devices but you need the Bluetooth address of it (so “PUP#1” is just an easy to remember tag that I choose for my “90:84:2B:06:AB:5D” hub).

You can get your BT address installing Nordic nRF Connect for Mobile app on your Android device and scanning nearby BLE devices while turning your LEGO hub on. If you changed its name with the LEGO App you will see a BLE device with that name, if not you will see “HUB NO.4” or “Smart Hub”, depending on the firmware version of your hub:

Now we go to Design View and add all components needed:

From the ‘User Interface’ section:

  • two buttons: ‘BtnConnection’ and ‘BtnRst’
  • one ListPicker

From the ‘Drawing and Animation’ section:

  • one Canvas
  • one ImgSprite

And from the ‘Sensors’ section:

  • one Clock

I added a few others that are really not needed, just used them for aligning and cosmetic purposes.  I also renamed the buttons names to better remember their purpose and changed some of their properties.

Now back to our Blocks view, we need to take care of what happens when our App starts:

We start a Bluetooth LE scan to find all BLE devices nearby. This is necessary later on when we want to connect to our LEGO device.

Then we create our list of Hubs (seen above), set the text of the Button used for the BLE connection, draw our Joystick at the center of the canvas and initialize our Clock.

This Clock will be used to keep the BLE connection active after we connect: we need to keep talking with the LEGO hub because after a pre-defined period without communication it will shutdown to prevent battery draining.

For now we just keep the clock disabled and set the period  to match the global variable “TRACKSPERIOD”.

We also define what happens when we click our ListPicker:

(we change the text to the friendly name of the chosen LEGO hub)

Now we define what happens when we click on our connection Button – we want it to connect to the device we chose whenever there is no connection yet and to disconnect when already is:

(we also activate or deactivate our Clock at the sametime)

I will not explain the blocks related to the Joystick – they are used to calculate the duty cycle (speed) of the two motors from the position of the joystick. These values are store in two global variables: ‘SpeedA’ and ‘SpeedB’.

The next important part is sending the calculated values to the motors.

The hexadecimal command used to control a WeDo 2 Motor (we should probably call it a “Powered Up Medium Motor) is:

0800810 p 115100 dt


  • ‘p’ is ‘0’ if we are using ‘Port A’ and ‘1’ if using ‘Port B’
  • dt is the hexadecimal representation of the duty cycle (a percentage value)

The AI2 BuetoothLE extension uses a list of decimal values so

8 0 129 0/1 17 81 0 dt

Lucky for us the extension also accepts signed or unsigned values so we don’t need to take care of the conversion when duty cycle is negative:

so every time the Clock reaches our “TRACKSPERIOD” value it sends the commands for the two motors. Setting a smaller period allows a better control but also increases the activity of the App so for too small periods it might not work properly. And, of course, setting a larger period will increase the latency of our control and might also cause our connection to drop.

Hope this explanation is clear enough for anyone that wants to try their own app. Feel free to make questions on my YouTube channel, I’ll try to answer the best I can.

Making an Android app for LEGO Powered Up

The new LEGO trains are now Powered Up based.

Like WeDo 2 and BOOST, this is a Bluetooth 4 Low Energy (BLE) device that uses the new type of 6-pin plug that LEGO announced a couple of years ago with the WeDo 2. At that time this new design was referenced as Power Functions 2 or PF2 but the final name is now Powered Up.

Unlike BOOST, the new smart hub included with the trains doesn’t include motors. LEGO found a way to arrange 6 AAA batteries inside it in such a compact way that the final size is exactly the same of the Power Functions LiPo or AAA batteries… with all the new electronics included:

Others like Sariel and Hispabrick already reviewed this device so I’ll just show how to to use it.

This new hub announces itself as “HUB NO.4”.  It will probably have a much better name but for now I will call it this way.

A good thing with “HUB NO.4” is that it  provides the same UUID services as BOOST. So most of the examples I wrote for BOOST work with Powered Up with just a few modifications.

For instance, the LEGO WeDo 2 motors can be used the same way as with BOOST:

gatttool -b 90:84:2B:06:AB:5D --char-write-req --handle 0x0e --value 0800810011510060

The handle (“0Eh”) is the same. The payload is also simillar, with the same 3 initial bytes (“080081”, hexadecimal) followed by a fourth byte that selects the output port (“00” = port A, “01” = port B), followed by the same 3 bytes (“115100”) and finally the last byte is the duty cycle (or speed) applied to the motor (“60h” = 100d = 100%).

Since I already had an Android app made with MIT App Inventor 2 for the  Vernie model of the BOOST set I made just a few modifications to make it work with “HUB NO.4”:

  • removed the blocks that controlled the head and cannon trigger
  • removed the blocks that sensed the colors
  • added the BT address of my “HUB NO.4” to the list of devices to pick
  • changed the motor commands used by BOOST (simultaneous control of pair A+B) by the motor commands of two WeDo 2 motors

That’s it!

This the Designer view:

and this is the Blocks view:

If you’re interested, I exported the project as an “.aia” file. It’s not polished (for instance the blocks still make references to Vernie) but you get a good base to start.

In my next article I try to explain how this App was created.