[Frank] wanted a classy way of telling the time, so he built up a LED Pocket Watch. The watch features 132 LEDs for displaying the time, two buttons to activate and change modes, a vibration motor, and a buzzer.
It’s controlled by a picoPower ATmega645P, which has enough pins to drive the array of LEDs, an internal real time clock, and low power consumption. The device is housed behind laser cut acrylic face, and sits in a 3D printed case.
To power the device, [Frank] used a rechargeable lithium coin cell battery. The charging circuitry is based on a MCP73831, which is an easy to integrate charge control IC. A USB connector is used to provide power to the board.
One of the bigger challenges of the design is driving the large array of LEDs. [Frank] uses Charlieplexing to group the LEDs and reduce the number of pins required. Another trick he used was offsetting the ISP header pins. This allows for programming the AVR without soldering a connector to the board.
[Frank]’s Instructables write-up is very detailed, and includes explanations of the schematic, PCB layout, software design, and case design. It’s a good read that details his design decisions.
After the break, watch [Frank]’s video overview of the project.