Electro-Legos

My oldest son is almost seven years old. Seven is right about when I got my first Atari 800XL and learned to program. Today's kids have much cooler choices for computers. Personally, I think that the ability for programs to interact with the physical world makes a huge difference in motivation.
I recently backed up a Kickstarter campaign for the Espruino Pico. While being "yet another" small microcontroller-based board, this one has quite a neat software stack: it runs a JavaScript interpreter and exposes a very extensive JavaScript API for controlling its I/O. I was thinking this would make a great tool for super-quick hacks that I sometimes need for testing purposes / one-off tooling. But quickly it dawned on me that this would be a perfect way to get my son into programming! The Espruino has an IDE that is a Chrome extension with Blockly support, allowing us to code without having to do much typing and without risking syntax errors (which is often a big source of frustration for beginners). I also found that it was fairly easy to add new blocks, so I quickly made a couple of useful ones (for example, there wasn't a stock block for controlling a servo).
And so we've been playing for a while, controlling the on-board LEDs with the on-board button, and later adding a servo motor. But blinking LEDs and moving a servo for their own sake gets boring after a while. Luckily, the tooth-fairy has kindly provided us with a kit of accessories which greatly extends the possibilities! Since my son loves Legos (who doesn't?), my idea was to allow him to embed the I/O devices in his creations. Not a new concept, but mine was totally DYI, taking only a few hours of work in my garage and costing next to nothing.
The kit I made (shhhhh, don't tell it was me!) contains:

• A micro servo, fitted with 2x2 Lego bricks on the top and bottom with correct alignment and a 1x4 brick on the arm. I used Gorilla glue for attaching the bricks to the servo, then "cast" the thing in hot glue for extra strength and cleaner shape. For alignment, I built a Lego fixture that held everything in place while the glue dries. For the casting, I found a cool trick you can do with hot glue: I pressed the workpiece with the molten glue against a piece of parchment paper placed on the desk. Once cool, the hot glue easily separates from the parchment paper, resulting in a really clean, flat surface.
• A selection of LEDs. I found that the "technic" lego pieces have holes that are the perfect size for a 5mm LED. With a bit pressure it goes all the way in and will never come out. I made a set including: a double-LED (red, green) piece, an auto-color-changing LED piece and an RGB LED piece. I soldered the appropriate (for 3.3V) current-limiting resistors to the back of all LEDs to make hook-up simpler for my son.
• Two push-buttons. It turns out those through-hole push-buttons fit perfectly between the bumps of a 2x2 piece, when placed diagonally. A dab of Gorilla glue, and we're done.

I'm really happy with the result and if it works out well I can easily add more pieces.

Here's what happens when you let dad play with the kids' toys...