by Frank Pelliccio
Last Updated 2012.12.04 21.13
What is Megawatch?
Megawatch is a 4-digit 7-sement LED wristwatch driven by an 8-bit Atmel ATMega48 AVR microcontroller.
The Megawatch PCB measures just 1.5" x 1.0" [38.1 x 25.4mm]
Megawatch is powered by a rechargeable flat, flexible 180mAH lithium polymer [LiPo] battery. The battery is taped to the inside of the leather band. The charging circuitry is on the PCB, and charges right from a micro USB power. The watch is good for about a week or two on a single charge with regular usage.
Each second, Megawatch illuminates a single LED segment around the perimeter of display, which fades very quickly. Each minute, the time is displayed for about 7 seconds, before slowly fading. The fading is accomplished by using a dedicated multiplexing IC. The 7-segment digits are common anode, and the anode is fed a PWM'ed signal coming through the multiplexer.
Time is updated using the two buttons on the right-side of the watch face.
The PCBs were fabricated using Laen's phenomenal OSH Park service, and hand assembled.
The microcontroller can be programmed directly via the AVR ISP 6-pin interface with a special bed-of-nails programming adapter with spring-loaded pins.
Here is the first prototype in action.