loading

Step 11: Potting the Watch

Potting the watch
To make the watch suitable for everyday use it needed a case. I visited AFF Materials ( http://www.aff-materials.com/ ) to buy polyester resin. A nice guy there suggested that I use a clear epoxy instead. According to him, the polyester resin shrinks ~5% which might fracture connections on the PCB. The clear epoxy only shrinks ~2%. He also suggested that gases from the polyester might damage components while it cured.

Having never worked with a clear epoxy before, I did some test castings. I started by casting some samples in an ice cube tray. Sunflower seed oil, silicone lubricant, and silicone bicycle lubricant were tested as release agents. One sample was done with no release agent. The silicone lubricants beaded in the bottom of the mold and left pock marks on the epoxy. The control suck to the bottom of the mold. The oil worked pretty well, but left a slight residue in the epoxy.

Next, I needed to know how to do a multi-layer casting with this material. A polyester resin is usually poured in layers. A first layer is allowed to set (about 15 minutes) to a gel. An object is placed on the first layer and a second layer of fresh resin is poured on top. The working time of my epoxy is about 60 minutes. I poured a first layer and checked it after 30 minutes - still soft. After about 1 hour and 15 minutes the first layer had stiffened enough to place an object on it. For this test I put the LED test board seen in step 2 face down on the first layer, and covered with a layer of fresh epoxy.

This worked great, the LEDs didn't pop off the board. I concluded here that absent a proper mold, the clearest surface I can make is the air/epoxy interface. The 'top' of the casting has a significant miscus. The miscus is limited to the very edge of the casing and is easily removed with a grinder.

For the first real test I needed a rectangular plastic mold. The best option I found was a 'smeer kaas' container. It wasn't perfect, so I made it smaller with a few layers of tape-wrapped foamcore. This wasn't a stellar mold, but choosing the top as the display surface gave me some leeway. The mold was lightly wiped with oil on a paper towel.

I ditched the multi-layer pour procedure from above. I soldered leads from the coin cell battery holder to the PCB. The cell holder was hot-glued (ok, stickie-tacked) to the bottom of the PCB. The battery holder was filled with stickie-tack, and the programming header protected with yet more stickie tack (plasticine would also work great). This was then placed, face up, in the mold. The stickie tack protecting the battery and header was pressed firmly into the bottom of the mold, anchoring the watch in place. Clear epoxy was poured into the mold until it covered the watch. The pin-headers were still quite long, but can be cut after the epoxy dries.

The watch released from the mold after about 36 hours. The protective putty was removed with a screw-driver. The edges were smoothed with a drill-press grinder bit. The watch was cast a little large to be worn as a wrist watch. I may try to cut it down if I can find a band saw. For the time being, it will be a pocket watch. The tape-over-foamcore gave a cool texture and ultra-clear surface. Next time I will try to make the entire mold using this material, something more in the neighborhood of wrist watch size.
designing mine with a mirochip TC622 temp sensor and and a accelerometer so i can have a pedometer, and shake to wake so the watch is normally off until i shake my wrist and the temp sensor will be activated with a button to display the temp and for the club mode option also trying to make a water proof case. props for the great idea.
Hey, would you mind uploading a schematic or circuit diagram? It would make things a lot easier with the building, in my opinion.
I made it! Working great! Thanks!
Is there any chance of preprogrammed PICs?
I had a bunch of these boards made, then all my orders cancelled on me. I can sell them for about $4 + Shipping
If those boards are still available i am definately interested. Let me know if they are available mattwagner92597@aol.com. Thanks
I'm definitely interested in buying one. Please let me know if they are still available.<br>adele dot thompson7 at gmail dot com.
Good Idea, maybe set up a website or something?
I am very impressed by the knowledge in the comments and the posting. Is there anything on this site about quartz watches? I have looked under watch repair and nothing of any value (for me) came up.
&nbsp;Hello Ian<br /> First nice work man,I like it this binary clock I am fan of binary clocks<br /> Second I need the schematic can you post in original size.<br /> And one more thin because I am not a profesional in programming can you see it this <a href="http://www.mastrogippo.it/2008/09/yet-another-binary-watch/" rel="nofollow">wrist clock</a> ,I want to made it but the code is in <a href="http://www.mastrogippo.it/files/bw.c" rel="nofollow">&quot;C&quot; </a>can you converted into hex?Please help me<br /> Regards maco bt
Step 1: i think it reads 9:42 but you say it reads 9:24?
&nbsp;Think about it - the least significant bit is at the bottom of the display, not the top.
Ahem, 20ppm of one year is more like 10.5 minutes, or about 50 seconds per month, or did I&nbsp;miss something?<br />
I&nbsp;suppose this won't work under water.&nbsp; ...but maybe you weren't trying to create a diver's watch.<br />
I made the watch <sub></sub><br/><br/>BUT,<br/>i cannot program it<br/>I have a PICKit 2 programmer, and the program that came with it does not support that type of chip.<br/> I downloaded a new program, but it does not support the PICKit 2 programmer<sub></sub><br/><br/>Any suggestions??<br/>
this watch roooooocks men!!!!! i am going to do it .. for sure.... <br/><br/>P.D. it&acute;s construction has any problem<sub> or something that we should know about ???? </sub><br/>
I built it, ant it worked on the first try. Be sure to read the PIC programming tutorials
Very nice. I built it.<br/>I made photos of it's construction: <a rel="nofollow" href="http://picasaweb.google.com/asafteirobert/ConstructiaCeasuluiBinar">http://picasaweb.google.com/asafteirobert/ConstructiaCeasuluiBinar</a> .<br/><br/>Sorry for the &quot;&Acirc;&copy; Twinsen&quot;. :D<br/><br/>Interesting thing is that i couldn't find a SMD Darlingthon transistor, so i used a normal one, and it works great, it's even too sensitive.<br/><br/>Have you updated the firmware any recently?<br/>
great job on them watches lad. hope i could use this info of yours to help me fix my broken <a rel="nofollow" href="http://www.gadgetepoint.co.uk/prod-oregon-daylight-projection-clock.php">oregon daylight projection clock</a>. great job again! keep it up! \m/<br/>
Wow! I really want to make this, but I can't seem to find the instructions! All I can decipher from this page is a brief history of the parts. Am I seeing/doing something wrong?
where can you buy the little leds-- like on the strip at the bottom Great i cant wait for the updates of this wow this is wiked
Well, as they say, if you cant build it, buy it :<br/><br/><a rel="nofollow" href="http://www.iwantoneofthose.com/binary-watch/index.html">http://www.iwantoneofthose.com/binary-watch/index.html</a><br/><a rel="nofollow" href="http://www.iwantoneofthose.com/square-binary-watch/index.html">http://www.iwantoneofthose.com/square-binary-watch/index.html</a><br/><a rel="nofollow" href="http://www.iwantoneofthose.com/binary-clock/index.html">http://www.iwantoneofthose.com/binary-clock/index.html</a><br/>
This thing is Brill!, I am going to try and make one, but where can I get the code to program the PIC chip?
One more question, how does one go about programming one of these chips? Is there something I need to buy to interface it with my computer?
There is a cct for a JDM2 style ICSP programmer included with the project archive. It has a readme.txt with details.
Wow nice little project there =)<br/>I'm wondering what software did you use for the 3d rendering of the boards???<br/>
The 3d images used in this instructable were made from the Eagle Board files with Eagle3D and POV ray:<br/><a rel="nofollow" href="http://www.matwei.de/doku.php?id=en:eagle3d:eagle3d">http://www.matwei.de/doku.php?id=en:eagle3d:eagle3d</a><br/>
Looks like a very neat project! I'd liike to try to build one of these inside a broken wristwatch or something. What are the dimensions of the chip? Thanks.
Thanks Parker, The chip is standard SO-300 package from microchip. Its a little wide for my taste, but that makes it even easier to solder. This was my first surface mount project.
Very nice idea. Good implementation. Well written instructable! Your touch sensors may be more complicated than necessary. Since the inputs to the PIC are MOS transistors, they have a very high impendence all by themselves, and you might get by with just finger resistance to a power rail and a big (~2M?) pull-x resistor or the internal pullups.
I noticed this when prototyping. The PNP alone would do it. I had not thought about using the bare pins - thats a great idea. I will give it a shot.
I forgot to mention the bad side, which is that the MOS gates in the micro are probablyt easier to damage via static than the bipolar transistors....
I've got to include a link to your charlieplexing instructable:<br/><br/><a href="http://www.instructables.com/ex/i/FA846F483AAB1029AC23001143E7E506/?ALLSTEPS">http://www.instructables.com/ex/i/FA846F483AAB1029AC23001143E7E506/?ALLSTEPS</a><br/><br/>This is different than the multiplexing used on the watch. I considered using it, but routing and driver design seemed easier for the straight multiplex.<br/>
Good project, maybe it will get reserved for a weekend in the future. Wud be a cool keyring when going to geeky functions.
one note: curing epoxy can get hot enough to damage a circuit. use slow-curing epoxy because it doesn't get as hot, do a test cast and check the temperature - if it gets really hot then use an ice-bath to keep it cool during the cure. larger amounts of epoxy get hotter than smaller amounts due to reduced surface-area to volume ratio.
Thanks Dan, good tip. This was 36 hour cure epoxy. I didn't notice any heat when I worked with it. I had never worked with epoxy prior, only (poly) resins.
Very, very nice. You may like to know that Crisco also doubles as a great resin release agent and is much easier to apply than oil, in some cases...
Hi Ian, Great looking little device....and so many functions! As I said before, the touch switches are an inspired ummm....touch. I'm still having troubles getting a programmer to work with my 16F88 microdot watch...but made up a parrallel port programmer PCB...hopefully will get something working soon. Only problem is I'll need to add a whole lot more functions just to keep up with you! Phil
Thanks phil,<br/><br/>Did you give up on the JDM2? Getting the proper voltage can be a pain if you don't have a desktop with serial port. Its a simple design if your computer can drive it.<br/><br/>What parallel programmer are you making? I've ordered parts for 2 or 3 ll programmers, but never built them. I never wanted to deal with the power brick.<br/><br/>Here's a cool function you could include:<br/><a rel="nofollow" href="http://ww1.microchip.com/downloads/en/AppNotes/00996a.pdf">http://ww1.microchip.com/downloads/en/AppNotes/00996a.pdf</a><br/><br/>Cheers,<br/><br/>Ian<br/><br/>
Absolutely amazing. Beyond the obvious geek cool factor of the binary display, I wonder if a small SMD display matrix could be used for scrolling alphanumeric time, etc. display. Thanks for sharing!
Thanks. The menu already scrolls text. Hex/DEC/bin selectable time display is on the firmware roadmap for v0.4.
I bow down to his suprememe geekiness.
that would ruin the point("Absolutely amazing. Beyond the obvious geek cool factor of the binary display, I wonder if a small SMD display matrix could be used for scrolling alphanumeric time", uless it was in binary)
<a rel="nofollow" href="http://www.ladyada.net/rant/?p=9">http://www.ladyada.net/rant/?p=9</a><br/><br/><a rel="nofollow" href="http://static.flickr.com/46/107067240_7564270216.jpg?v=0">http://static.flickr.com/46/107067240_7564270216.jpg?v=0</a><br/>
very cool dude. very cool
(Mod +5: Uber-geek!) This is an excellent design and make Instructable! Everything about it says "I am elite geek"! Suggestions for further mods: "Auto Night mode" - detect the ambient light and set the duty cycle of the LEDs using that. "heart rate sensor" - useful for your clubbing idea, but also great for when exercising. You might be able to do this using the voltage changes on the Darlington? A small re-design of the board, to remove stuff from the corners, would allow it to be trimmed to a much smaller footprint, and allow better wrist wear. Much kudos. A*.

About This Instructable

37,893views

82favorites

License:

More by ian:Thermal Tweeter networked Twitter printer @tweet_tree: Twitter controlled Christmas tree Hackable Christmas card & ornament 
Add instructable to: