Octolively derivative at ARMTechCon

Mouser display based on Octolively

We dropped by ARMTechCon last week to check out a tip sent in by email (thanks, Barry!) that Mouser Electronics was displaying something that looked like our Octolively modules.

Kids interacting with LEDs
Photo courtesy of Mouser

Mouser staff had been inspired by an installation of our Interactive LED Panels to create something interactive that they could show off at Engineers Week at the Fort Worth Museum of Science and History. They used the Octolively as the basis for their project, and the kids loved it of course.

Blue "M" in LEDs

For trade shows, they built up a display with a mix of blue and white LEDs to show off the Mouser “M”. Based on the foot traffic it got while I was at the booth, it is quite popular.


They made some minor changes from our original Octolively design and used different connector types to highlight Mouser’s product lines. The heart of the project is still the 40-pin DIP ATmega164P (perhaps anomalous at an ARM conference) running our Octolively code, which gave the Mouser folks a chance to play with some microcontroller programming.

Interactive display based on Octolively

It’s always exciting to see a derivative of one of our projects in the wild. Thanks to the Mouser folks for sharing their project story and sending the museum picture for us to share.

Micro Servo Earrings

These earrings — Perfect for radio control and robotics enthusiasts — are made from little servo motors, partially hollowed out for lighter yet weight.


We begin with a “9 gram” class micro servo motors. This is a standard type of servo motor; the same kind that we use to lift the pen or brush on the EggBot and WaterColorBot.

Inside of one of these you’ll find the actual DC motor itself, a set of plastic gears, a potentiometer (pot) connected to the output shaft, and a little circuit board that controls it all. The gear train is used to convert the high-speed low-torque output of the motor into its high-torque low-speed output, and the pot reads the orientation of the output shaft so that it can be controlled (servoed) to the correct position. However for today, we’re primarily interested in the case, and most of what’s inside doesn’t really matter.


servo-3 servo-4

The lower part of the case comes off with four very skinny, very long screws.

servo-5 servo-6

And then, you can pull out the tiny little circuit board.


The DC motor slips out easily, but the three wires to the pot are soldered in, and need to be clipped.

Incidentally, it’s straightforward to hack servo motors, repurposing the circuit board such that (1) the two outputs to the DC servo motor actually control something else and (2) that the input signal from the pot comes from something else. You can read our article about how to make a one-ton servo motor for a good example.



And then there is the matter of the cable. We don’t actually need that much cord hanging out the end — and it weighs something — so we can clip it shorter.


servo-10 servo-11

A dab of hot glue secures the cut-off end of the cable to the bottom of the case.



And the finishing touches: Reassemble the case, add the servo horns and finally the earwires. The final weight of each one is about 6.5 g, and the total weight of the components that we removed (motor, wires, circuit board, and cables) is about 5.6 g. As we have left it, the output shaft feels solidly held in place. Turning the output shaft still turns the gear train, and its motion is limited to the servo motor’s original range of travel; about 2/3 of a turn.

You can make it even lighter — all the way down to 5.4 g per piece — by opening it up further and removing the pot and all of the plastic gears except for the output shaft. It looks mostly the same from the outside (with the exception that the gears are no longer visible), but does not feel nearly as nice: The output shaft is only loosely held on its axis, and now able to turn freely through a full circle.

One might imagine taking it the opposite direction too: Building in a little battery and microcontroller, so that the servo motor would turn on its own while dangling from an ear. That version is left as an exercise for the reader, hopefully one with short hair that won’t get tangled.


If you liked this article, you might like some of our other related projects: Fimo fractal earrings, Chip earrings, Hard drive earrings, and Bobbin earrings.


Inside the 741

Ken Shirriff has written an excellent exploration of the 741 op-amp, including decapping a metal can package AD741. There’s a very cool interactive viewer so that you can click on the components in the schematic or on the picture of the die to see what each one is and does.

…The 25pF capacitor in the 741 has a very small value but takes up a large fraction of the chip’s area. You can see the capacitor in the middle of the die photo; it is the largest structure on the chip. …

Our very own XL741 is referenced in the footnotes, too.

Evil Mad Scientist Open House: November 19

Evil Mad Scientist Door

You’re invited to our annual open house!

When: Thursday, November 19, 5 pm − 9 pm
Where: Evil Mad Scientist Laboratories
175 San Lazaro Ave, Suite 150
Sunnyvale, CA, 94086

You can check out our latest projects, play with the giant Digi-Comp II, meet Zener the cat, and share in food and conversation.