Wristwatches with LEDs are often digital timepieces. Their faces would possibly show seven-segment numerals or use LEDs to point the time as binary dots. Nonetheless, Armin Bindzus’s newest watch challenge takes a special and engaging strategy. The LED_Watch creates a quasi-analog show with 240 LEDs on a uniquely made circuit board.
Bindzus achieved LED_Watch’s quasi-analog show by making a PCB with 240 concentrically organized surface-mount LEDs. Two internal “rings” and two outer “rings of LEDs make up the watch arms. The internal ring creates the hour’s hand, the mixed rings are the minute’s hand, and the outer rings briefly flash because the second’s hand.
Laser and chemical etched circuit board (📷: dropletwatch.com)
If you happen to look carefully on the naked circuit board, it would seem like a typical PCB with a white solder masks. However it’s not a typical printed circuit board! Bindzus manufactured it in-house with a laser cutter! As an alternative of attempting (and failing) to etch the board straight with the laser, Bindzus used a mixed laser chopping and chemical etching method discovered from a earlier challenge.
This board began with Bindzus making use of lamination to either side of a copper-clad board. A laser cutter ablated isolation areas to create an etching masks. Then, iron trichloride creates isolation trenches by etching away the uncovered copper. A second move by means of the laser cutter ablates the lamination on pads. The remaining lamination turns into the solder masks! Lastly, Bindzus applies a zinc paste (for pipe fittings) with a scorching air gun to complete the uncovered copper pads. The distinctive result’s an impressive-looking non-printed circuit board.
Inside LED_Watch (📷: dropletwatch.com)
A Microchip ATtiny1614 8-bit AVR microcontroller (MCU) drives LED by means of HEF4094 shift-and-store registers. The MCU saves energy by staying in sleep mode till an Analog Units (formally Maxim) DS3231 real-time clock wakes it up by way of interrupt. That interrupt happens each 1.4 milliseconds to handle the LEDs. A tilt swap turns off the increase converter for the LEDs to avoid wasting energy. These methods imply a 74 mAh LiPo battery offers as much as 20 days on a single cost!
On the heart of LED_Watch’s face is a light-dependent resistor (LDR). Since this resistor limits the present by means of the LEDs, it additionally controls their brightness. This intelligent relationship additionally means the watch has an computerized brightness management based mostly on the ambient mild!
Like all watches, LED_Watch wants enter controls to set the time. Bindzus designed capacitive contact areas as an alternative of mechanical buttons. This design selection provides the watch a contemporary person expertise and makes it extremely water-proof!
For extra details about the design, go to the LED_Watch web page on dropletwatch.com. Bindzus offers extra pictures, the schematic, and an in depth circuit design clarification.