Lego Mindstorms RCX computer (robotics)

I like playing with Lego in the 70s and 80s. I mainly knew fischer technik with electronics.
By coincidence I found this.

Version 1, I think from 1996. 6x batteries AA. Based on Renesas H8/300.
Does anybody has experience with this?
Later versions are not that lego style.


Well, that’s odd. Just had to check my cupboards… I thought I didn’t have an original RCX. And yet it turns out I do have the 727 piece 9719 set, which is supposed to contain one. But it’s not in there! I can’t think where it might be.

I did later get a NXT 2.0 and for the longest time it’s been set up as a Rubik’s cube solver, using David Gilday’s Mindcuber design.

Earlier I’d bought the 8094 set, hoping for some reason that it had the kind of programmability I’d always wanted, but that one turns out just to be a sequencer - it just predates the RCX and Mindstorms idea, I think.

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Yes, I have one - I upgraded the firmware to the 1.1 version (I think - it was some years back now!) and used to use NQC (Not Quite C) to program it. Great fun!


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I was a graduate student at the MIT Media Lab when LEGO introduced the original RCX 1.0, which was based on work that my research group, Lifelong Kindergarten, did to create 68000-based “programmable bricks.” There had been several generations of these, identified by color (e.g. gray brick, red brick), so we called this (no surprise) the “yellow brick.” All our previous bricks ran the Logo programming language, and naturally we wanted to create a Yellow Brick Logo. The problem was that we wanted to stay on very good terms with our corporate sponsor, which initially forbade alternate firmware. Fortunately, they soon embraced the maker ethos, and allowed 3rd party languages to run on their “brick.”

It was not easy for my colleagues to reverse engineer the yellow brick, but we had lots of RCX prototypes around (e.g. some without the power jack shown here), so one day I asked my advisor if I could help by using a heat gun to brush all the surface-mount components off the PCB so we could see where all the traces ran. This did indeed clear up some mysteries.


I’ve only ever heard about the RCX, having never encountered anything more than fairly simple robotics sets. One project using RCX that intrigued me was Styx-on-a-brick which exposed features of the RCX as a file system using the 9P protocol.