Wristwatches with LEDs are normally digital timepieces. Their faces would possibly show seven-segment numerals or use LEDs to point the time as binary dots. Nevertheless, Armin Bindzus’s newest watch mission 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 inside “rings” and two outer “rings of LEDs make up the watch palms. The inside 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)
When you look intently on the naked circuit board, it would seem like a typical PCB with a white solder masks. However it’s not a normal printed circuit board! Bindzus manufactured it in-house with a laser cutter! As a substitute of making an attempt (and failing) to etch the board instantly with the laser, Bindzus used a mixed laser slicing and chemical etching approach discovered from a earlier mission.
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 go by 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 sizzling 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 HEF4094 shift-and-store registers. The MCU saves energy by staying in sleep mode till an Analog Gadgets (formally Maxim) DS3231 real-time clock wakes it up through interrupt. That interrupt happens each 1.4 milliseconds to handle the LEDs. A tilt change turns off the increase converter for the LEDs to save lots of energy. These methods imply a 74 mAh LiPo battery gives as much as 20 days on a single cost!
On the middle of LED_Watch’s face is a light-dependent resistor (LDR). Since this resistor limits the present by the LEDs, it additionally controls their brightness. This intelligent relationship additionally means the watch has an computerized brightness management based mostly on the ambient gentle!
Like all watches, LED_Watch wants enter controls to set the time. Bindzus designed capacitive contact areas as a substitute of mechanical buttons. This design alternative offers the watch a contemporary consumer expertise and makes it extremely waterproof!
For extra details about the design, go to the LED_Watch web page on dropletwatch.com. Bindzus gives extra images, the schematic, and an in depth circuit design clarification.
