I also need 5 resistors (R1, R2, R3, R4, R5) to limit the current to the LEDs, so they operate within their ratings and not burn out. (click on the LED matrix image above, it is an animation that shows you how my LED matrix works) This means I need 35 pins to drive 132 LEDs. My design arranges the LED in a 30 anodes by 5 cathodes (I may refer to these as "rings") "matrix". The solution is to group the LEDs so I can multiplex them. One option is to select a microcontroller with 132 pins, simple, right? But the microcontroller will be gigantic, and the design will look bad. The challenge lies within the number 132. Starting off, the simplest way to do this is with a microcontroller of some sort, we'll worry about which one soon. I am using CadSoft EAGLE 6.2 to draw the circuit schematic and lay out the PCB design. The problem we are trying to solve is "how to light up 132 LEDs in a way that indicates time?" this is a LED pocket watch, not a mechanical pocket watch. PCB, laser cutting, and 3D printing services can be found online and I am already very familiar with all three of these techniques. The purple edition is because OSH Park makes purple PCBs, I wanted a case to match the color, why not make two and see if I like it.Īs I am coming up with my goals, I also have to consider the materials and equipment I have access to. I made one that is black and green because green is the cheapest PCB color and I have a preference for black. I'm not limited on cost, and they will physically fit in the design, so why not? The buzzer and motor feature are basically just fancy additions because I can do it. The easiest battery charging method today is probably by using USB, all you need is a cord and a USB port. So I decided to use a rechargable battery. Nobody likes replacing batteries, especially when it is stuck inside a case. The casing also has a hole, so I can attach it to a chain. A casing is required to protect the circuitry from junk inside my pocket. Most of the time it will be in my pocket. I wanted this to be something I use daily, it must be durable. So I decided I wanted it to have the size that fits comfortably in my hand, just like my phone, and I wanted a single button to activate it, just like my phone. Right now I check the time using my phone, I'm sure a lot of you do too. I want three rings because the different radiuses helps me distinguish between the different "hands" faster. I explicitly chose not to use bicolor or tricolor LEDs. Although following the behaviour of an analog clock might sound good, it makes it a bit slower to visually interpolate the current hour. There are 12 LEDs for the hour "hand", not 60. You will feel confident that the watch is working, because you can visually see each second tick away. As the seconds change, it creates motion, which gives the viewer a feeling of confidence and pace. I want 60 LEDs for the second "hand", and some of the other designs do not feature a second "hand" at all. I really want a clear indication of the current minute with no guessing or estimation involved. It is very common to see LED pocket watches that do not have all 60 LEDs for the minute "hand", some have only 12. The top three goals are to look good, user friendly, long lasting. There are some flaws in other designs that I didn't like, so I have my chance to improve upon those flaws. This isn't the first LED pocket watch to exist (I saw this one), I want one of my own, and when I want something, what I really mean is I want to build something. Everything is open source, and also ready to be sent out for fabrication. This will include the microcontroller source code, circuit schematic, PCB layout, laser cutting vector file, and 3D models. The pocket watch is constructed of a PCB, two pieces of laser cut clear acrylic plastic, and a 3D printed casing.Īll the files are also available from my Github (there is a single ZIP download option on that page). This pocket watch also feature a buzzer and a vibration motor, which are used for the alarm feature, and the motor causes a short "tick" as each second passes by. There is a low battery indication feature. The battery life depends on how heavily the pocket watch is used, but if you leave it alone, it is estimated to last several months. The battery is a rechargable lithium ion coin cell battery and it is charged from a micro USB connector. There is a button on the top to activate the pocket watch, and a button on the back to change modes and settings. It has 12 LEDs to show the hour, 60 LEDs to show the minute, and 60 LEDs to show the second.
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