This week's EYE ON NPI can handle the pressure of being featured - it's the ICP-10111 Barometric Pressure Sensor (www.digikey.com/en/product-hi...) with astonishing accuracy that makes it excellent to use as an altimeter. According to TDK, this "pressure sensor can measure pressure differences with an accuracy of ±1 Pa, an accuracy enabling altitude measurement differentials as small as 8.5 cm, less than the height of a single stair step." 1 Pa is really good and competitive in the market .
Even though we call this an altimeter, its technically a pressure sensor that uses the changes in pressure over altitude to compute. Earth's ambient barometric pressure changes with altitude - because air gets thinner the higher you go. (en.wikipedia.org/wiki/Atmosph...) There's a simple calculation that can be used to determine relative altitude changes and, if you know the sea level pressure (which usually doesn't vary much) you can use that to determine the absolute altitude. The better and more accurate your pressure readings, the better your altitude calculation output.
GPS can also be used to calculate absolute altitude, by measuring timing differences from 3 or 4 orbiting satellites. (www.gps.gov/systems/gps/perfo...) However, GPS only has an accuracy of about 10 meters, which is good for large equipment like planes but not good for humans, who are only about 2 meters tall. Also, of course, you need to have GPS fix which consumes a lot of power and requires one to be outdoors. Often times, even if a system does have GPS, a pressure-sensing altimeter will be included in the system. Also, pressure sensors can of course be used underground or underwater - try getting a GPS fix there!
This isn't a new kind of sensor - we've stocked a wide range of barometric sensors over the years such as the popular BMPxxx (www.digikey.com/en/products/d...) and the DPS310 (www.digikey.com/en/products/d.... But this one seems to have improved the precision, with an impressive 1 Pascals at around sea level instead of the common 2 or 3 Pascals. This apparently can give you ~10 cm differential measurements. Note that this is differential not absolute - you can tell if you've gone up or down and by how much, but it doesn't necessarily translate to precision absolute measurements (which is a different specification).
One nice improvement over most sensors we've seen is that these come in four packaging options: physical size/pinout variations in 2x2mm and 2x2.5mm and then waterproofed to 1.5m depth versions with three micro-laser-drilled holes in the top. Obviously the PCB that the sensor attaches to may not be easily waterproofed, but this sensor could have a gasket covering it, or it could just be less sensitive to ingress moisture and dust.
Another big deal is...all four ICP-10111 versions in stock at Digi-Key! (www.digikey.com/short/r248d9n8) Right now most of the other sensors we like to use are totally unavailable due to parts shortages, but you can get some of these sensors and they seem to be I2C-usage pin-compatible with the BMP280/DPS310 and BME390. Note the SPI pins are NC/reserved so its not purely pin-compatible, and of course there's some firmware updates you'll need to code up. So if you need a altimeter, and want one with waterproof casing, these could be an easy swap into an existing design to upgrade it! Order today an you could have them in hand by tomorrow morning.
See at Digi-Key at www.digikey.com/short/r248d9n8