Making the new Nixie watch water-resistant

[David Forbes]

A few years ago, I designed a rechargeable Nixie watch. It's a lot
sleeker than the original design. It also has a Micro USB jack for
charging.

http://www.cathodecorner.com/nwl/index.html

I let my son wear one for a couple weeks, and it failed due to corrosion
on the PC board, from saltwater getting inside.

I decided that sealing it would be a smart idea. I looked around the
webosphere, and found that several companies now sell waterproof USB jacks!

JAE, TE Connectivity, EDAC and others have products with a rubber seal
around the shell, for insertion into a milled or molded oblong hole. The
EDAC unit also has mounting ears to keep it from breaking off.

The watch design also had a couple other problems, but I'm addressing
those with a different CPU chip.

I just spent the day redoing the layout of the logic board to make it
take less room in the lower right corner, for an o-ring to surround the
case.

I'll post renderings when it's further along.

--
David Forbes, Tucson AZ

[gregebert]

What about the mechanism to turn-on the display ? Is it a water-resistant pushbutton, or something else ?

My original plan was to use skin resistance across 2 metal contacts to turn-on. The problem I encountered was that when the watch energized it created excessive noise, so the technique was flaky. It worked nicely on my prototype (how many times has that happened before......)

I ended up using a pushbutton, so mine definitely is not water-resistant. And due to another flub, I'm unable to recharge the battery because one of the charging terminals has an electrical open. Either I smash the case open, or drill a small hole to contact the battery terminals. But I do get to find out how long it runs on 1 charge...My prototype has been running more than 3 months on it's initial charge.

I decided against wireless charging because I was afraid of induced voltage in the PCB traces,  and even the components, as well as not having enough room for a Li-ion battery-charge controller.

[David Forbes]

Greg,

I use an accelerometer to activate the display when it's at a 45 degree angle,
which angle is set by the user when setting the time. It works great. There are
a pair of time setting buttons on the right side. They will have tiny O-rings. I
will also have a big O-ring around the case, between the front and rear halves.
The watchmaking industry sells these O-rings in ~0.5mm cross section.

I have been using an old Casio calculator watch as a reference, to see how Japan
solved these design problems decades ago.

I'll post renderings of the case as I do the redesign. I hope to have this
project wrapped up this summer - it's been languishing for over 2 years!

[gregebert]

How much standby current does the accelerometer require ? On my design, I shutdown everything except the clock and have just under 2uA standby. I wonder if I got too stingy with energy savings.

[David Forbes]

The accelerometer uses about a milliampere of current when activated, so I turn
it on five times a second by powering it up via a CPU port pin. It takes a few
milliseconds to stabilize.