Introduction: Neopixel Watch, Done Right
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lights contest, microcontrollers contest, and the jewelry contest
There are many problems with a traditional watch: the watch strap must be switched out to match every outfit, the crown can snag on sleeves, and water can permeate into the case. Furthermore, the glow-in-the-dark elements are hard to see in the early morning after being in the dark overnight. Traditional watches are also difficult to see when not using glasses if you need glasses to see the very thin hands.
With water proofing, battery life, and completeness being the main goals for this watch that is unique compared to other DIY neopixel watches. Using neopixels to be able to change the color and brightness of each marker it we can solve most of these problems; as well as using an accelerometer to keep water out of the case. With 12 markers the watch can tell time with a accuracy of an average of 2.5 minutes. Using the accelerometer to activate the neopixels with the flick of the wrist or a double tap (similar to action seen in smartwatches) the neopixels are turned on with a sweeping animation. Additionally a constant neopixel at a light level of 1 will turn on at the 12 o'clock possession to be able to see the relative location of the others in the dark.
Step 1: Progress Thus Far
- Short battery life
- Fragile hardware
- Bulky design
- hard to set time
- not water resistant
Neopixel Watch Progress
Methods of an easy to implement an input method were brainstormed:
- Button - would be too difficult to waterproof without a custom cap
- Encoder - (like apple watch) cool idea but hard to fit into a watch with standard components
- Accelerometer - (tap detection + gestures) easy to waterproof and implement into the watch
After seeing a few other watches with an accelerometer as input I got the idea to use one, as it solves all the problems of being difficult to mechanically implement while being robust and waterproof.
After learning how to use eagle and making a schematic and board layout was designed the boards were ordered. Parts were purchased, mainly from Digikey, and were cheap and quickly shipped. Unfortunately, upon getting the boards weeks later, a mistake was made the on the pad layout of the real time clock, so in order to be able to test the circuit desperate things were done... We had to bend the leads of a DIP RTC in order to fit the misaligned pads, same with one of the resistors as well. Despite these challenged, we persevered and became closer to our goal!
Step 2: More Problems
Problems with pad placement. The bootloading pins on the board were placed very poorly and the ATMega328p was difficult to solder. Bootloading was also an unnecessary process that could be sidestepped by using a pre-bootloaded ATMega328p from a Arduino Pro Mini clone. The result: a second board.
Left is the poorly soldered board with bootloading pins, right is the thinner, sleeker board. Unfortunately, the black board shown above was the incorrect size for the watch case. The board did not sit correctly on the lip of the watch case. We ordered new boards that were 0.5mm larger in diameter. Meanwhile, I began working on and revising the CAD model of the watch case and I also began considering watch strap ideas.
- About 7.1mm thick with an outer diameter of 40mm
- A small slot in the bottom of the case for a charging port
More about the charging port: It is a contact method that allows us charge while retaining water resistance.This solution is cheaper than other water resistant methods, such as removable back and wireless charging
We have made a charging interface for the port using pogo pins. Here is a picture of the charging interface on the case:You may be able to see a problem with the charging interface however. The pogo pins have a high chance of being being when placed on the watch case with this current design. The next design included a lip to preserve the pogo pins.
Step 3: Component List
1×Atmega328p desoldered from arduino pro mini clone
1×Accelerometer ADXL345 Desoldered from a brake out board
1×Real Time Clock DS1308
12×Neopixel LEDs WS2813 with built in capacitors
1×3.3v Voltage Regulator MCP1700T3302ETTCT-ND
1×CRYSTAL 8.000 MHZ 18PFXC2105CT-ND
1×2mm Concave HeadersED1354-ND
1×Real Time Clock Backup Battery728-1053-ND
10×8pf Ceramic Capacitors311-1639-1-ND
1×Crystal 32.7680KHZ 12.5PF535-10104-1-ND
10×10k Ohm Resistor311-10KJRCT-ND
1×Round Lipo Battery 3.5mm thick with protection pcb http://www.powerstream.com/round-li-polymer.htm
1×Glass Lense http://www.esslinger.com/watch-crystal-flat-round...
1×Watch Case Might be able to find some cheap watches online that are drop in.
Step 4: Instructions
Soldering the circuit board.
Load a blink program onto the donor arduino pro mini clone, to make sure it works before you start doing anything else to it. After confirming it works load the neopixel strand test code on pin 7. Next use a hot plate to solder the Atmega328p as well as to desolder the ADXL345 from its brake out board. Next use a solder stencil to apply solder paste to the circuit board. I used a laser cutter to cut a stencil out of some adhesive vinyl, or you can order one from your board house.
Get the watch case 3d printed or milled if you are able to. I recommend getting it 3d printed in metal from shape ways in a material that is polished as it will save a lot of work down the road, you might be able to also find a cheap watch that has the needed inner dimensions, if so you would need to drill a hole and file it into a slot to be able to put the charging and programming connector.
Soldering the connector on the back using the 2mm concave headers is the hardest part as the headers need to line up with back of the case height, for this it is best to bend the header pins at a right angle and solder the tips to the pads on the back of the board. Then test fit it into the case making sure it lines up in height.
Adding the RTC back up battery and main lipo battery onto the back of the board.
Hot glue the battery to the back of the circuit board, making sure there is room for the headers on the side, test fit the watch module into the case keeping in mind that the headers need to line up with the slot on the back of the case.
Add the watch lens onto the front of the case making sure to apply even amount of glue to the inner lip that the lens sits on, apply it with a tooth pick and put very little because it could get on the view-able part of the lens.
Using paint to fill in the concave headers on the back of the case, let it dry then using 2 part epoxy to fill in the space between the headers and the watch case to make it water proof.