how to build v4

This post is part of what I hope to be a series that will de-mystify and put in one place all the things I’ve learned constructing these things, and at the same time lay out the steps to building a working version of the watch as it is now. First, we’re going to talk about tools, and then I’ll lay out the current BOM, and how to go about getting some of the parts and material that are hard to find.

Tools

note: I don’t get any referral money from any of my links; wherever possible, I link to where I got something, or a known reputable source. A lot of these links will be to Adafruit, because they have all the best stuff.

The difference between a good tool and bad tool is measured in the hours of frustration the bad one will cause you. Yes, you can accomplish a lot with minimal tooling, and the good stuff doesn’t have to cost a lot. For example: this pair of tweezers is really very good, and very reasonable at less than $4. So, the list, with some annotations:

  1. Soldering Iron – Why would you need one of these for a surface mount project? There are four through hole joints to be made, but you’d need it anyway, to clean up the inevitable bridges.

  2. Solder wire – For the through hole joints. If you’re in the EU, you’ll want the lead free ROHS compliant stuff: here.

  3. Solder Paste – This stuff is kinda amazing. It’s a low-temp solder paste that makes SMT work a lot easier to control. Instead of a precise reflow curve to avoid damaging components, you just heat till it’s all liquid, wait ten seconds, and turn off the heat. If that link dies, search digikey for “SMTLTLFP”. It’s also ROHS compliant!

  4. No clean Paste Flux – Another thing that’s cheap and handy to have around. It helps solder flow onto a joint, or onto your solder wick.

  5. Solder Wick – This is a braid of fine copper wires which wicks away solder when you heat both at the same time. You can remove excess solder, or even desolder some components with it.

  6. Tweezers – I actually have two of these on hand, because I don’t want to do without them if I mislay them somewhere in the junk pile that is my desk. You’ll use them for placing all of the components, removing stray hairs from the board, plucking hot components from molten solder (don’t worry, we’ll get there).

  7. Soldering Iron Stand – Nobody ever told me how great these were, so I’m telling you. A stable place to put your iron while it’s hot is essential. Note: Sometimes the spring on the inside will pop off; just push it back on. It’s safe to use that way, but not as stable as having both springs.

  8. Hot Air Rework Station – This is probably the only really big ticket item on the list. You might be able to do without it, but remember what I said about frustration?

  9. Halogen lamp – This is what is going to heat the whole board up for reflow. Note that the Home Depot is bad at online ordering; you’re better off going to a store. Any single bulb, 500w lamp should do the trick. SAFETY WARNING: hot lamp is hot all over, except maybe on the handle and base. It will set fire to things that touch it, so use caution.

  10. Programmer – You can also use an arduino with the chip pulled, both methods are very similar.

  11. Wire Snips – Another item I did without for years, a good pair of flush cutters. Their usefulness can’t be overstated.

Parts

Now that we’ve talked about the specific tools, there are a few parts that are peculiar to this BOM that can’t just be stuck in a spreadsheet.

  1. The PCB – This link is to v4.4, which will soon be replaced by 4.5. That said, 4.4 is fully functional, but the screen folds the wrong way. I'm fairly sure it'll fit in the case still (target was < 4mm). I'll update the link when it's there. 4.5 is there! New balun, fixed screen connector. OSHpark is the best, and given the size of these traces, I wouldn’t recommend any of the cheaper options for PCB fab.

  2. The paste stencil – Not required, but without a stencil, putting paste down takes about half an hour. With it, it takes about a minute. You’ll have to grab the cream layer from the Github Repo and upload it yourself, since oshstencils doesn’t have shared projects.

  3. Battery – These are often out of stock, I don’t know why. There’s a 110mah version that you could also use.

  4. Case – No link, because this is one of the places the ‘Y’ in DIY happens. Also, my case designs are rubbish, and I don’t have any for the v4 series movement. I’ll probably post an STL when we get to that phase of the howto.

  5. RFduino – This is the brains of the operation. To get the chip with a bootloader, you’ll need to buy one of these and desolder the RF sheilding, and then desolder the chip itself. This is where you’ll be glad you got the hot air station, or borrowed a friend’s. You may be able to hear up the RFduino on the halogen light to desolder it; it’s worth a try. After desoldering, you usually have to clean some solder off the center pad with solder wick.

The rest of the BOM is here, but some of the links are stale. I last updated that for version 4.1, and we’re at 4.4. The BOM is pretty stable at this point; I don’t see changing it much.

And that’s it! probably a $200 investment, if you can borrow a hot air station, or more like $300 with it. Order 10 or more of the components that cost less than a dollar, since they’re cheaper that way, and you’ll need extra.

Posted by Matt on 2015-10-15 05:19:52 +0000