Hi y’all! Joey here. I’ve owed you a Sensor Watch backer update for some time now. The TL;DR is this: the LCDs and accelerometer sensor boards are complete, and all components for the Sensor Watch Pro manufacturing run have been delivered to my contract manufacturer in Georgia. Sensor Watch Pro should enter manufacturing next month, and while the ship date is slipping from April to May, it’s not likely to slip any further. Read on for the juicy details!

What I’ve been up to

First off, I feel I should apologize for the radio silence. All I can say is that I’ve spent this time focused on turning the gears on shipping this product, and it hasn’t left much time to sit and write an update. Some of y’all may also be aware that *gestures vaguely at the world* things have been a little chaotic since the last backer update. When it became clear in November that the tariff situation might change dramatically, I began racing to get everything needed for Sensor Watch into the country. This was not easy, and the timeline was made more difficult thanks to a circuit board fabrication error that delayed our final panels by a month.

But first, let’s talk about the things that are done. The accelerometer sensors made it through customs in December, and the LCD’s did the same in early January. Last month I hired my buddy Ben (who’s been wearing Sensor Watch since 2022!) to help with the testing, packing and shipping of these items. So far he’s bagged up 700 custom LCD’s, one for every backer, and he’s tested about 1,700 of the accelerometer sensors. Next week he’ll begin labeling and bagging those, and we’ll be very near to having all the accessories ready to ship.

The one missing part is the main board. This is challenging: we had a couple of delays there. My first order of test panels came back in December with drilled holes that were outside the promised tolerances. It took a couple of weeks of back and forth — across a 12 hour time difference! — to resolve the issue. It also required a second round of test panels, which for the advanced process we need for Pro, took a couple of weeks. You can imagine the nail-biter of a time that was.

In the end though we were able to resolve the issues. 200 panels — enough to make 2,000 Sensor Watch Pro boards — managed to clear customs just three days before the first round of new tariffs were imposed. This means we now have everything we need to manufacture Sensor Watch Pro, right here in the USA.

My contract manufacturer, Cyber City Circuits, built the first test panel last month, and it’s looking pretty good:

The next steps look something like this: I’ve assembled the test jig that Cyber City Circuits needs to test and flash these boards, but I’m still finalizing the test procedure. I know: it’s me. The blocker is me. I’m racing to get this done as soon as I can, with the knowledge that every day of delay finishing this test jig, is a day of delay for y’all.

I promise to get this done as quickly as humanly possible.

Sleep and Activity Detection

At the same time I was doing all of this, I was also testing out some of the new features enabled by the accelerometer sensor. The biggest one, the one I know folks are probably most excited about, is sleep and activity tracking.

Fun fact about the accelerometer in Sensor Watch: we can control how quickly it samples acceleration, ramping it up to hundreds of samples per second, or down to just one or two. Why does this matter? Power consumption: at a sampling rate of 200 Hz, the accelerometer sensor consumes anywhere from ten to 90 microamperes, which seems like a small number until you realize that Sensor Watch Pro’s entire power budget is just seven microamperes — and even less when it’s sitting on your dresser in low energy mode.

To preserve any hope for year-plus battery life, we needed to figure out how to do more with less. The goal: get usable sleep and activity tracking while sampling at just 1.6 Hz. Doing it this way would add just 380 nanoamperes to the power budget — a miniscule amount of additional power draw, that would have a negilgible impact on battery life. The good news is I think we’ve nailed it. The trick was in making careful use of the two accelerometer interrupt pins on the Sensor Watch 9-pin connector:

• First, we set up an interrupt when the accelerometer experiences an orientation change. This fires when your wrist changes orientation, such as standing up or rolling over in bed. We increment a counter whenever this interrupt triggers.
• Then we set up a status pin, that detects whether the accelerometer is stationary, or was moving recently. By polling this once a minute, we can count the number of stationary minutes.
• We also use Sensor Watch Pro’s on-board temperature sensor to capture temperature information at the top of the minute, which can tell us whether the watch is stationary because the wearer is asleep, or stationary because it’s sitting on a dresser.

With these three signals, we’re able to capture granular information like this:

To be clear: we don’t have enough space to write all of this data to the watch, all the time. For the purposes of this testing, I’ve been logging it at a high level of granularity, and as a result the file system fills up after six days. Still, with some clever algorithm’ing, I sense we will be able to distill this down a few bytes of data covering bedtime, sleep duration and activity level. My hope is to get this down to a handful of bytes per day, and store at least a year of sleep and activity data on the little file system.

Watch this space.

Data Upload via IrDA

We’ve also successfully tested data upload, through the front glass, via the built-in phototransistor in Sensor Watch Pro! The software support for this is in its infancy, but the demonstration watch face can receive a file over IrDA and store it on the local file system:

This should open the door to easier upload of TOTP secrets, and I expect we’ll see a more advanced “data bank” type watch face in the near future, one that can read screens of data from the file system. Right now, the easiest way to upload data is using an Adafruit Circuit Playground and a high-intensity infrared LED, connected using a simple wire harness. Total cost from Adafruit: under $30.

Logistics and Ship Dates

I know: the one you’ve all been asking about. Previously we had set April 14 as the expected ship date for Sensor Watch Pro. Realistically, that’s not likely to happen. With the test procedure still being finalized, I think it’s likelier that we will start manufacturing and testing the Pro boards in early April, with the aim of shipping out to backers in May. Everything is here, and the blockers aren’t huge. I’m going to do everything in my power to ensure that this product ships to Mouser in May; with a couple of weeks of processing time at their warehouse, I hope to have Sensor Watch Pro in your hands and on your wrists in time for it to accompany you on sunny days and starry nights this summer.

Thank you all for your patience, and for staying with me on this journey. I cannot wait to get Sensor Watch Pro to you all.

- Joey