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At Elektor, everything can turn into an electronic device.

This round shaped earring with a diameter of 31 mm basically includes eight LEDs, a voltage regulator, an MSP430 microcontroller and some passive components, and it's powered by a CR2032 battery. At this point there are two firmware versions available, but it's also possible to reprogram the device by means of the UART-interface. Current software versions include four different light patterns in both directions (clockwise and anticlockwise), switching between them with the pushbutton. It's about a low power design, and it needs only about 4.45 mA at 2.8 V (12 mW) when LEDs are multiplexed.

You may see this video during the development stages, taken while the program wasn't still complete.

This article was first published as Elektor.POST No. 1.

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CORRECTIONS
(We would like to thank Mr. Colin Mitchell for his comments and contribution!)

• The text mentions that the current through the LEDs is limited by means of 100 Ω series resistors. The correct value is 220 Ω (as noted on the schematics).
• Figure 2 caption may be hard to understand in the English version, please see the following: "only add a very small blob of solder to the board to prevent a short-circuit with other contacts".
• The debouncing is indeed implemented by software and not by means of C5, as the text notes.