I'd like to figure out how to make a pressure sensor for very low cost (essentially disposable), mass produced piece of medical equipment.
The problem: this can't use any parts which aren't already available in huge quantity. In other words only parts with > 100k and preferably > 1M in distributor stock. This probably rules out the obvious approaches of using MEMS pressure sensors for cell phones (or does it? any super-high volume MEMS devices?). Probably most specialty parts are out; commodity parts only (resistors, capacitors, generic op amps, generic transistors). It is okay to fabricate components from raw materials (eg - a force sensitive resistor from conductive foam) if the materials are readily available. It helps if all the parts used are extremely cheap (bom cost < $10).
What the sensor should do is sense pressure differences. It needs to pick up changes of <1cmH2O (100 Pa) in pressure, and it needs to have response times <1 second. For this 0.1 cmH2O precision and readings every 0.1 second are great specs. The typical operating pressure is 0 to 40 cmH2O. The physical form factor of what this connects to would be a short 20mm tube - as short as possible; 20mm x 20mm is good - with tapered connectors on both sides. I assume this would need a mechanical component like a diaphragm or piston which is somehow interfaced to a PCB.
It's okay if this doesn't have a very accurate zero, and other specs like linearity, drift, offset, scale error are non-essential as long as roughly 1cmH2O changes can be detected between 0 and 40 cmH2O. It is okay if each sensor needs an individual calibration.
Idea #1: diaphragm the position of which is read out using some version of capacitive touch - read out capacitance
Idea #2: diaphragm which compresses a force sensitive resistor made of anti-static foam - read out resistance
Idea #3: conductive diaphragm which touches a different number of conductive pads on the pcb depending on how far it's deflected - read out which pads are shorted together
Idea #4: conductive diaphragm the end to end resistance of which is read out depending on stretch
Bounty if rather than an idea, you build a working prototype. Huge bounty if you do it within the next day or two.