Craving Some Retro-Geek Chic Up Your Sleeve? Come to Your Senses and Cop a Sensor Watch!

Joey Castillo is a firm favorite feature here on Hackster.io

A true champion of the open hardware movement, we're no stranger to his previous works — a collection of Oddly Specific Objects that just get the job done.

We've previously written about his Open Book — an open source e-reader that (in this instance), proves you can judge a book by its cover. Before that, we branched out when we reported on his equally-to-task, yet cheekily christened Hiking Log — the name of which might be a running joke, but its purpose is anything but.

Up until the last year or so, Castillo has been a never-ending source of activity, shipping out well crafted project after project.

That's not to suggest Castillo has in any way been slacking for the past year, oh no no no!

He's been incredibly busy, just a bit more behind the scenes than usual!

This one is something to Watch!

We all love watches. So much so, that there even appears to be forming something of a watchmakers guild — with a good few folk turning out techno timepieces over on Twitter!

While many folks are choosing to trick out their wrist-worn wearables with features such as Wi-FI, there are a firm few who find the form factor and finesse of models such such as the iconic Casio F-91W something of a feature in itself.

We've previously reported on efforts to give this somewhat no-frills timepiece a bit of a tech-infused touch up, with makers such as node carrying out some "passive" modifications — adding NFC, and a sneaky µSD card carrying compartment.

Granted, not quite Johnny Mnemonic levels of tech, but still quite the step up on the sales pitch of the original, stock F-91W.

Low power, high spec

While the original F-91W watch made use of a very limited set of parts, it didn't need to do a huge amount. A three-button interface offered the user a limited set of features, but for a simple watch with simple features, that is all that's needed.

This cheap, ubiquitous watch does two things better than its mechanical, luxury Swiss counterparts.

First, it sells very, very well — with best guesses placed around the three million units a year mark!

Secondly, it actually outperforms the mechanical movements found within those much more expensive watches, with timekeeping that stays accurate to some +/- 1 second a day!

Once you really dig into it though, the F-91W is a fairly straightforward set of bits, with a straightforward set of functions — a solid enclosure, a segment LCD, and a simple PCB all come together to tell the time.

Looking at the PCB below, there isn't much to see. A slim picking of passives sit dotted around in support of the somewhat single purpose MCU, mounted underneath that black epoxy blob.

Given the visible lack of anything else to report on, it's clear to see that there is some space for improvement on the original circuit design - and that's just what Castillo has gone and done here with the OSO-SWAT — AKA the Sensor Watch, the latest in the family of Oddly Specific Objects.

This watch is a time traveler.

(Well, not literally, but we're allowed such artistic license with words these days, that I'm going to stick with that sub-heading.)

What would the F-91W look like if it were designed today, some 32 years after its initial release? Well, we think the Sensor Watch does a pretty darn good job of answering that question.

Starting with a blank canvas, the only limitation being that of the existing physical board outline, Castillo has set his sights on some more suitable components for his brand of smartwatch.

Low power at heart

Whereas the original F-91W will likely have had a simple ASIC at heart, maybe a more modern day derivative deserves a more modern day MCU — and when tasked with toiling away on the mere trickle of power that can be sourced from the coin cell that is used in this watch, there will likely be a preference on parts that pack low power onto their feature list.

A Microchip SAM L22 makes perfect sense here, as it supports a range of peripheral configurations that make this low-power quest possible, not least its built-in segment LCD controller — enabling it to drive the stock LCD of the F-91W.

Having full control over every segment of the stock segment LCD found in the F-91W makes for some interesting opportunities — and the design choice has proven to be worth the majority of the I/O found on the 64 pin package of the SAM L22.

It's allowed Castillo to offer a whole range of alternate watch faces, that expose the additional functionality that is offered by the modern, 32-bit MCU that sits under the hood!

Alarms, temperature, even a solar orrery (didn't see that one coming, did you?) — that reports the current planetary positions of the members of our solar system — it's pretty amazing seeing the range of ways in which the original LCD segment arrangement has been repurposed.

Whereas a ground-up smartwatch design would these days probably specify a pixel-rich, bright and colorful TFT display, complete with power hungry backlighting... — sticking with the segment LCD keeps the Sensor Watch power consumption down in the uA range, edging towards single digits!

The internal coin cell may not be of huge capacity, but with power consumption that low, the life time could be estimated in years, as opposed to at best, days of nearly any other smartwatch.

Expand your horizons

Not content with the aforementioned functionality that the SAM L22 offers on its own — there are a bevy of bolt-on boards in the works, that let the Sensor Watch sense just what is what, when it comes to its surroundings.

These L-shaped FPC boards enable the Sensor Watch to be fairly flexible in it's application — freely reconfigurable, by simply swapping out the application specific, Oddly Specific Object add-on modules.

Shown above, for example, a Bosch BME280 sensor module allows the watch to measure temperature and %RH (relative humidity) data! This data can then be piped directly to a watch face, to be displayed in real-time.

Alternately, one could choose to log some time stamped data within the flash memory found on the Sensor Watch, before sending it out to a PC for analysis, making use of that crafty USB connector, visible at the top of the Sensor Watch PCB.

Looking back to the Sensor Board connection system though, we can see that the choice of I/O mapped to the connector means that there is great support for many of the SAM L22 peripherals. This is important, as native, hardware peripheral functions are certain to take less power than say, bit-banging SPI up in the application layer.

Making moves

A sterling showcase example of what the Sensor Watch can do has been demonstrated with an add on board that features a three axis accelerometer.

This module could allow the watch to say, show the time when placed in a certain orientation — that's an easy one though. With enough data though, the full potential of the Watch can be unlocked...

The above plots are taken from the watch while it is being worn and being moved in a number of different activities — logging loads of lovely motion data to flash, to be read out over that USB connection — seen below.

Picking over the plots, we humans can clearly, visually make out the difference in these graphs — our brains are great at recognizing such data! The crazy bit here is that Castillo is teaching this ability to the Sensor Watch!

With a bit of MCU machine learning magic, courtesy of Edge Impulse, all of the data collected by the various add-on modules of the Sensor Watch can be analyzed, and algorithms designed to be deployed on the watch hardware enable it to do more than just display the data it senses.

Gesture recognition, activity tracking, trend predictions of atmospheric conditions or even gas sensing are all now possible, on a standalone watch, with battery life that we'd never have imagined possible.

As the collection of prototype boards below demonstrates, there's clearly a huge amount of potential for users to design and add whatever feature or sensor they can think of!

Thoughtful design

As if it wasn't already evident, there's a fair amount of thought that's gone into the Sensor Watch project.

There have been considerations of how to coax readability out of the Casio LCD segments. Quests to track down every single errant fraction of a microampere of power consumption have been waged.

It's quite the mental exercise to think about how to fit something truly complex in function into the comparatively simple form factor of the F-91W.

But we'd say Castillo has done a cracking job. The physical board itself follows the trend of the Oddly Specific Objects making things as user friendly as possible — even the Sensor Board connector pinout is listed there in the silkscreen.

That's hacker-friendly — and then some!

Get your hands on this bit of hacker chic!

Castillo has a crowdfunding campaign currently going on that will let you get your grips on the Sensor Watch hardware for a respectable $35.

Admittedly, you will still need a donor F-91W to work with, but that will likely run you a smidge over $10 — it's certainly one of Casio's most popular watches, and as such, is priced to reflect that.

Casio aren't exactly in the business of selling spare parts though, so a full watch is probably required — the Sensor Watch hardware just slips in place of the stock Casio PCB!

For that investment, you get a smartwatch that can run for a year, and you know, actually works primarily as a watch, not one that tries to replace your mobile phone in terms of features and content — and battery life!

If you want to know more about the Sensor Watch project, and all of the many other things it is capable of, check out the campaign page and make sure to give Castillo a follow over on Twitter: @josecastillo.

And once you've caught up on the story behind things, there's a wealth of information to be found in the project repo, forum and wiki — oh my!