NODE Brings Us His Latest Twist on the Classic Casio F91W, a True Timepiece for the Changing Times!

We love to wax about watches over here at Hackster.

In whatever format these wrist-worn chronographs present to us, there is always going to be some fun to be had in picking apart the design choices made, when people are faced with trying to fit all their tech into such a diminutive form factor!

While we usually see people trying to shoehorn in ESP32 modules, or perhaps a custom PCB complete with some silicon from Nordic Semiconductor, this latest tip from NODE — The Data Runner — a classic Casio F91W, with a few hidden tricks up its sleeve!

The F91W may not look like much at first glance and we cant help but feel that the unassuming nature of the watch is one of the reasons behind NODEs mods — the stealth factor of being able to hid extra function behind such a simple facade gives extra points in the "discrete" rating of this project.

In fact, the untrained eye would likely not even look twice at this watch — the mods are very close to keeping the original stock appearance.

So what is is that NODE has managed to mod to his liking with this timepiece?

NFC? Now you see me...

NODE aims to turn this watch into the smuggling tool of the times — a low-profile data cache, both in terms of dimensions and visibility, without having to sacrifice your precious grey matter for the sake of sneaking a few precious documents about...

The first trick he has employed, is the very clever, passive addition of a NFC coil, in place of the original front bezel of the watch face.

NODE has created s a custom NFC communications coil, crafted out of a 0.6mm thick PCB. The board contains a custom tracked coil, which is able to serve as an NFC antenna — able to be attached to a variety of NFC EEPROM ICs that are now on the market!

If you're stuck for choices, something like the 8kB ST25TA64K, from ST Microelectronics should be a good choice for this application, though there is still some room within the watch to shoehorn in whatever type of tag is required for your application.

NODE envisions even perhaps dissolving the chip-and-pin tag and coil from your contactless payment card, though we've had experience here in the UK that our systems require the card to be "reactivated" after a certain contactless limit — needing the pin to be re-entered via a chip-and-pin payment. It's worth checking the details of your contactless payment system before dropping the card in a bath of acetone!

If your data exfiltration needs are somewhat capacity driven, an 8kB EEPROM might not be enough to coverently carry your cache of files about with you.

To that end, NODE has installed a 3D-printed riser, in between the rear face of he watch and the frame itself.

This additional few mm of space is used to cram in an electrically non-functional micro SD card socket. It might seem a little odd at first — it's a lot of trouble to go to in terms of mechanical integration, when the card is electrically inactive, so... why, you might ask?

I thought the same thing, but on reflection, I can think of a number of cards that I have managed to damage over the years, simply for lack of somewhere suitable to store them.

My wallet has definitely cracked a few cards in half over the years, and my pockets have no doubt resigned a few units to the ESD graveyard — the typical behavior of one of these cards is to just turn into a space heater next time you try to mount it!

Having a purpose designed receptacle, in an easy to carry location actually isn't a crazy an idea as it first seems when you watch the video NODE has put together in detailing these mods.

Thrown in for good measure are a few more basic tweaks to the timepiece — an upgrade to the back light LED trades out boring old green for striking white, though likely at the trader of a reduced battery life.

One suggestion of note was to retrofit a small vibration motor in-place, though NODE notes that the watch doesn't have quite enough juice to have the motor vibrating as intended.

Given the relatively high current draw of a motor, and more so when loaded with an offset weight, we can see that the typical silver oxide, or lithium manganese dioxide chemistries often employed for coin cell batteries might struggle under such high-drain scenarios.

NODE has put up the design files for all the parts needed for you to try these mods out on your own F91W — though take note, these parts are designed to work with the genuine article — the many clones an imitation watches that pay homage to this style often have slightly different mechanical measurements, so these mods are unlikely to fit in the knockoff units!