Engineering
Notes from building Patch.
Design decisions and lessons from the hardware, written by the people making it. Patch is in development, so these are the ideas and the reasoning, not results.
Sensing ·
Why we build a test board before the real one
Why the light sensor’s layout waits for a small test board, read on a real arm, and why its first version never went out.
Read the post
Sensing ·
Simulating light before building anything
Billions of simulated photons, a simulator checked against a known case, and the list of questions only a real arm can answer.
Read the post
Process ·
Every check has to catch a planted mistake
Why no check on Patch’s design is trusted until it has caught a mistake we planted on purpose.
Read the post
Power ·
Charging without taking it off
Why Patch charges on the arm, and what that changed: a clip-on charger, gentle charging, and a thermometer that knows when to wait.
Read the post
Power ·
Making a small battery last weeks
The power budget behind Patch: every part counted, almost everything asleep, and the one cost that scales measured before the battery is chosen.
Read the post
Radio ·
Room for the radio
Why the antenna needs a strip of board with no ground copper, how a review caught ours being too narrow, and why distance from the body matters most.
Read the post
Hardware ·
Sticking to skin for weeks
What the adhesive has to do, why the edges are where it fails, and why only real arms over real weeks can choose it.
Read the post
Sensing ·
A clean heartbeat reading, from the upper arm
Where the LEDs and the light sensor sit, why their spacing matters, why stray light has to be blocked, and why we use three colors.
Read the post
Hardware ·
Flex, not rigid: why the production board has to bend
Why the production circuit is a thin flexible one rather than a rigid board, and everything that decision changed.
Read the post
Layout ·
Fences beat router instructions
Telling the router to avoid sensitive areas failed. Building fences that make the bad routes impossible worked, once we learned to trim them.
Read the post
Sensing ·
Why Patch has two temperature sensors
Skin temperature and air temperature, and why the pair tells us more than skin alone.
Read the post