Having recently been advised I need to use a CPAP machine, I decided to toss together a pressure tester as one of the machines we have I was unsure if the calibration was correct.
Here is the first rough test version. The slot the BMP180 is inserted through is just taped up at the moment. Later, I intend to make a full case.

The pressure sensor I have used is the BMP180 as that is what I've got on hand.
The processor is an Arduino Pro mini, and a small I2C OLED display is added.

The sensor housing has a 4mm hole to allow the airflow.

Push the sensor housing into the end of the CPAP hose.
Then, power up the Ardiono without the CPAP running. The current air pressure is read and used as a reference.
Next, turn on your CPAP machine and the display will read the air pressure.

The Arduino code is supplied. You will need the included libraries installed to Arduino IDE via the library manager as normal.

Deltaprintr

Deltaprintr Kit

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Source file https://www.tinkercad.com/things/2dQq8NaDeFQ-cpaptester