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:
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).