Overview

Sometimes you need to sense pressure when it's wet. And sometimes you need to know the relative changes in pressure as well as the absolute pressure. For the times you need to do both (or either), the LPS35HW is the pressure sensor for you. Combining protection from water intrusion with support for high precision relative and absolute measurements, this sensor will do what you need. With drivers for CircuitPython, Arduino, and Raspberry Pi, and support for I2C or SPI (Arduino only SPI support, for now) you'll be measuring pressure in moist situations in no time.

The sensor itself is advertised as Water Resistant but the breakout board for testing out this sensor is not! If you want to use it in wet environments you'll need to pot the rest of the board in a wateproof epoxy!

The LPS35HW has a fraternal twin, the LPS33HW. In nearly all respects the LPS33HW is the same as the LPS35HW however the LPS33HW has a bonus feature: a nozzle that can be used to seal it against an enclosure or perhaps a properly fitted tube of some sort. You'll want to make sure to use an appropriately sized o-ring to ensure a good seal. Like the LPS35HW, the LPS33HW chip inside is encased in a protective gel, however in the case of the LPS33HW, the gel is mentioned as being

...designed for and proven to protect electronic components from long-term exposure to harsh environments such as water mixed with chlorine, bromine, commercial washing detergent and fuels, solvents and chemicals.

Wow! That's a resilient sensor!

The LPS33W like its sibling is advertised as being protected from all kinds of horrible things however THE BREAKOUT BOARD IS NOT. For use in icky environments, you'll want to protect the rest of the board with appropriate measures. Since the LPS33HW has a sealable port, you may be able to use the information in the application note on the downloads page to make a suitable enclosure

Capable sensors

The ST LPS35HW is a water resistant barometric pressure and temperature sensor that is also safe to use in wet environments. The sensing element is nestled safely in a ceramic package and is encased in a waterproof gel that prevents water that gets into the sensor from interfering with readings. It does not carry any ratings for resistance to moisture so you probably don't want to take it to the bottom of the Mariana Trench, but it should work well for normal wet situations like weather stations or high humidity.

Similarly the LPS33HW is ensconced in a protective gel that protects it from harsh environments. Additionally it is called out by the manufacturer (ST) in the datasheet as being suitable for applications such as weather station equipment or a moist, mouth-adjacent activity that we don't encourage. Let's just say it seems well suited for things like sip-and-puff switches.


Along with not being afraid of getting wet, the LPS35HW and LPS33HW have 24bit pressure data and 16 bit temperature data, allowing it to deliver pressure readings with +/- 0.1% hPa accuracy. It can measure from 260 to 1260 hPa and is able to withstand pressure up to 20 times their measurement range.

To help you take measurements to your requirements, the sensors also offer an adjustable data rate, as well as a low pass filter to remove noise from the signal. Finally, the onboard temperature compensation makes sure that your readings are always good and won't vary as the temperature changes.

We placed these sensors on a breakout board with a 3.3V regulator and level shifting circuitry so it can be used by 3V or 5V power/logic devices. A small piece of header is also included, so you can solder it in for use with a breadboard.

A Family Affair

The LPS33HW also joins our growing family of boards with SparkFun qwiic compatible STEMMA QT connectors, allowing you to combine it with all sorts of other sensors, and even displays, all without needing to solder! Just plug and go/blow!

This guide was first published on Jun 11, 2019. It was last updated on Jun 11, 2019. This page (Overview) was last updated on Dec 05, 2019.