07/02/2017 at 19:01 •
After some time off it's time to continue this project. Since last update i was left with soldering led matrix. Plan was to use custom ss stencil to hold LEDs in place while heating them with hot air station, but it didn't work(kind off). Since stencil was chemically made(etched) holes at the edges of stencil weren't big enough to fit LEDs so i had to improvise. Basically i mounted only one LED for each segment and shorted other one. This means that there are now 256 LEDs on PCB. Next step is to assemble the module, see how matrix looks under diffuser, test and improve the design. Here is the video and some pictures of the process:
06/05/2017 at 22:15 •
Here are some picture and video of soldered led matrix driver board. All components were placed by hand using fine tip tweezers. It took me around 45 min to setup and 15 min to place all of the components. There were no solder bridges after reflow, only few unsoldered pads(U13 last picture) that needed to be reheated with soldering iron. Next up is writing test code while I wait for stencil for led matrix PCB(It takes long becouse it is free). Soldered led matrix PCB will be shown in "Soldering - Part 2." project log.
06/03/2017 at 21:17 •
Here are the pictures of PCBs that arrived few days ago. Since these are the first PCBs that I ordered from OSH Park, I decided to inspect them in detail under microscope. Gold plating on copper is smooth, evenly distributed and nice to solder on (tried test soldering few components on one PCB). Silkscreen is smooth, "high resolution" and looks way better than on Chinese PCBs (Chinese mostly use dot matrix printers so theirs silkscreen looks "pixelated"). Only downside is that solder mask isn't perfectly aligned with pads, but that wont be a problem.
05/18/2017 at 22:02 •
While waiting for PCBs to arrive I designed enclosure for the watch. I made few printed watch enclosures in the past and from my experience, I don't think one can be made to look good and be reliable. Moving plastic parts like holes that hold strap springs just wear out after a month of use. Therefore I designed enclosure that is compatible with apple watch accessories (straps, strap adapters...). Since strap adapters are metal and made for commercial watch they will be robust and available cheaply on ebay.
Main parts of the enclosure are:
- Clear cover - 1 mm thick acrlyic sheet covered with tinted vinyl wrap.
- Main enclosure body - With slits for straps or strap adapters.
- Back cover - 1 mm thick aluminium sheet with attached magnets and custom etched logo.
- External magnet - Used to activate four hall effect sensors.
- Sound port - Small hole next to external magnet for piezo sounder.
- Magnetic USB adapter - Looks cool.
04/30/2017 at 21:00 •
I have ordered PCBs from OSHPark. They are expected to be done by May 19th, adding shipping time I except them by the end of May. For now only gerber files are available in project repository. I will upload entire project file with embedded step model of enclosure when model is. Finished gerbers look something like this:
All of the components were ordered from Mouser except LEDs used for matrix (Vishay TLMS1000), connectors and battery. LEDs were ordered from TME since they were cheaper (0.0715$ @ 500pcs compared to 0.138$ @ 500pcs). Here are some pictures of lit LEDs soldered on soe random PCB (I wanted to see how well epoxy diffuses light):
04/19/2017 at 20:21 •
Since the last update I was working on driver PCB for led matrix but there are still few touch ups to do. PCBs will be ordered from PCBWay or OSH Park. PCBWay is dirt cheap (10 PCBs are 5$ + shipping), while PCBs from OSH Park have nice ENIG surface finish.
Changes: I have replaced original peizo buzzer with new one that can be reverse mounted on PCB (more space efficient) and replaced 100mAh battery with 300mAh one (writing on silk is wrong. It is 300 not 350mAh). New battery is 4 mm thick(3 mm old) and more space efficient(covers more free space on PCB).
- 0.8 mm PCB thickness
- 0.15 mm signal, 0,3 mm power trace width
- 0.15 mm trace clearance
- 0.3 / 0.6 mm vias
Watch thickness should be something like this(top to bottom):
- 2 mm Plexiglas (don't think I can get thinner plexiglas)
- 0.2 mm of clearance
- 0.6 mm component height on LED matrix PCB
- 0.8 mm LED matrix board thickness
- 1 mm of clearance for components on driver board
- 0.8 mm driver board thickness
- 4 mm battery thickness
- 0.5 mm of clearance
- 1 mm for removable aluminium back cover
= 10.9 mm total thickens. For comparison Apple watch (42 mm version) is 12.46 mm thick.
Some picture of PCBs: