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 ·
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.
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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.
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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.
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Sensing ·
Why Patch has two temperature sensors
Skin temperature and air temperature, and why the pair tells us more than skin alone.
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