Some projects I did during my bachelor's in ITU.
An electronic flow meter is built to measure the gas flow rate during a person inhales and exhales.
A differential flow-meter is built with two connected tubes varying in diametersand they equipped with Bosch BMP180 sensors.
The sensors are connected to an Ardunio Mega to process the data. Then the data is sent over USB to a PC where they are plotted on the spot in MATLAB.
In order to check and calibrate the system, a low cost simple mechanic respirometer is bought and connected to the tubes.
For details, you can read my report.