Spirometer with ESP32 and Venturi Tube
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Spirometer with ESP32, display 3.5". It is a blower based on the Venturi effect. Consist in a blower and a unit box.
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Spirometer with ESP32-S3 and Venturi Tube
This project is based on a Venturi-effect flow tube connected to an independent central unit, featuring a 3.5” Freenove TFT display and an integrated ESP32-S3. An SDP810-500 Pa pressure sensor is used to measure the differential pressure between its two ports. It does not measure liters directly; instead, flow rate and volume are estimated based on these pressure readings and an experimental factor derived during calibration using a 1.5L syringe. Professional-grade calibration is very costly (€500), so a calibration method using a 1.5L syringe was adopted. While the precision is not extremely high, it provides a reasonable approximation of actual values. Naturally, these results cannot be medically validated; the device is intended solely for home use.
The Venturi Effect:
When air passes through a narrower section, its velocity increases. In an ideal horizontal model, the static pressure decreases in that zone. Assuming approximately constant density, the continuity equation relates the two sections (1 and 2).
The data obtained includes:
Estimated FVC (Forced Vital Capacity): Total net volume.
Estimated FEV1 (Forced Expiratory Volume in 1 second): Volume exhaled during the first second.
Estimated PEF (Peak Expiratory Flow): Maximum flow rate recorded during the measurement window.
Duration of the exhalation (s).
Peak pressure (Pa).
Total recording duration.
The device accommodates disposable cardboard mouthpieces measuring 28 x 26 x 65 mm.
It consists of a main body containing the Venturi ports, a housing for the pressure sensor, and a handle 3D-printed using TPU 95A. During the slicing process, the design was split: the upper clamp section is printed in white PLA, while the handle section is printed in black TPU. The output cable connects to the port on the... Freenove board (see wiring diagram).
The 3D-printed enclosure for the central unit—printed in two colors—features a USB-C port for programming the board, two holders for a stylus, an on/off switch, and a rear cable entry point. On the front, there is the Freenove TFT display and an indicator for the 18650 lithium battery status. The bottom houses the battery holder for an 18650 Li-ion battery.
Required materials:
1 Freenove 3.5” ESP32 320x480 TFT touchscreen board (https://amzn.eu/d/04Kj58dS)
1 Sensirion SDP810-500Pa sensor
1 Mini on/off switch
1 18650 lithium battery
1 3.7V BMS for an 18650 battery
1 1S battery capacity indicator
1 18650 battery holder
30 cm of silicone tubing (2 mm inner diameter)
M3 screws, 3 mm plastic-threading screws
IMPORTANT: The .ino program file is not included. Once assembly is complete, you can customize the on-screen display layout, how data is presented, and which parameters are measured.
In my setup, the information is transmitted via USB in CSV and PDF formats.