Controlling a MicroScout from an RCX using VLL

The MicroScout brick has one motor, a light sensor, display and can make R2D2-like beepy noises. It has 7 built-in programs, and a mysterious “P” mode in which it can be respond to external commands and can even be programmed via the light sensor. LEGO calls this Visible Light Link (VLL), and it has been used in other bricks as well, like the Code Pilot.

So I decided to hook up a standard LEGO 9v Light 2×1 brick to one of the OUT ports on my RCX, and see if I could get it to work. Here is the setup (and my first attempt at Leocad):rcxvll building instructionsThe lamp doesn’t really show up well in the above picture, but it’s simply one of these.

Now basically the light needs to flash in certain patterns to transfer information. For finding out what those patterns are I need to acknowledge Doug Eaton who did a great job of figuring it all out and putting a great write-up online. Another great resource was Barnaby Walter’s page, who achieved the same using the LEGO fibre-optic elements.

I have written a rcxvll.nqh library which contains all the VLL commands the MicroScout recognizes, together with a little test program which runs a sequence of the direct commands which you can use to test connectivity.

To successfully use it all together, make sure to build your setup first, turn on the bricks, upload program to the RCX, set the MicroScout to P mode, then run the RCX program.

You can barely see the light flashing in the video, but it is!

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