My day job at Vivotronix involves building devices for physiological signal acquisition, particularly in the form of next-gen wearables. So, to play into that I thought I'd try to make a stripped-down wearable for this contest.

Normally devices that I make are packed to the gills with electronics. At the minimum, they contain: microcontrollers, oscillators, WiFi/BLE radios, memory modules, mosfets, diodes, LEDs, batteries, power filtering circuits, battery charging circuits, and on top of that a litany of different sensors depending on the application.

For this contest however, we can make things even more simple. 

Really, by the guidelines of the contest we could throw a coin cell battery, an LED, and a switch into a 3D printed watch case and call it a day. 

That wouldn't be as cool though.

So instead, we're doing essentially the same thing, but with a biomedical twist: by replacing the switch in our conceptual diagram with an amplified electrophysiological signal we can make an LED beat in tune to the user's heart. 

This is accomplished via a very good chip I've come to know, the AD8232. To simplify what the chip is and what it does, you can think of the chip is a fancy amplifier. It takes the minuscule electrical signal generated by the user's heart, beefs up the electrical signal, and re-outputs it. This new signal is high enough voltage to register on a computer or microcontroller's analog to digital converter. Since we don't have a microcontroller in the watch, we just drop in an LED instead. Rather than seeing a number on a computer go up and down with changing voltage, we see a change in light intensity. 

After the concept was solidified, work started and progress was swift. Within a day I had a viable Eagle schematic and board, and within two, the CAD for the enclosure was finished as well. Normally right about now is when I'd start on the firmware, but thanks to the analog nature of the implementation there's none to write!

All that remains is to order the board from MacroFab and test it.