The sensor which I am looking at here is a PS-2152 Pasport Spirometer. Spirometers are devices used to measure the volume of air inhaled or exhaled by the lungs. The device uses differential pressure transducers to measure the flow rates or the amount of air breathed in or out in a given duration of time.


Spirometry is the most basic and common methods to understand pulmonary lung functions. It may be useful to do the following:

1.To determine how well the lungs receive, hold, and utilize air 2.To monitor a lung disease 3.To monitor the effectiveness of treatment 4.To determine the severity of a lung disease determine whether the lung disease is restrictive (decreased airflow) or obstructive (disruption of airflow)

The above has been taken from this Respiratory Disorder link. More details can be found on it.

How a Spirometer works

The Pasport Spirometers comes with a mouthpiece which has a thin screen in the middle it. This mouthpiece gets connected to the flow head and the electronic enclosure. When the user blows into the piece, a small amount of resistance to the airflow is generated across the screen. Resistance leads to pressure difference which is measured by two airlines that lead to the 'differential pressure transducer' in the elctronic enclosure. The flow rate is determined by comparing the measured differential pressure to an onboard stored reference data. Flow rates over time are integrated to measure the total volume exchange.

Hence a number of readings and measurements concerning the ventilatory function of the respiratory system can be obtained from this method.


Graphic recordings of expirations are called Spirograms and help to visualise measuremtents.


The Forced Vital Capacity (FVC) measures the total volume of air exhaled during the maneuver. Speed of the expiratory airflow is quantified by the Forced Expiratory Volume in One Second (FEV1), and by the relationship of the FEV1 to the FVC, expressed as the FEV1/FVC ratio. These measurements are usually compared with average values "predicted" for a subject based on their sex, age, height, and race. An FEV1/FVC that is below the lower limit of a subject's normal range for this ratio indicates probable airways obstruction.

More Details on this can be obtained on Principles of Spirometry

More Details on the Interpretation of Pulmonary Function Test (PTF)/ Manual

Types of Spirometers

There are broadly two types:

1. Volumetric Spirometers: Directly measures air volume as a function of time. Eg Water-sealed, dry rolling seal and bellows spirometer

2. Flow-Type Spirometer Measures airflow during a period of time and integrates the flows to get expired volume. Eg pneumotachometer, turbine, hot wire anemometer spirometers.

Difference between pneumotachometer and hot wire anemometer spirometers I am putting this extra bit of information as it confused me for a while. I was under the impression that that principally differential pressure sensors were the only mode of breath measurment. I saw this link with the anemometer and it clarified some of that confusion. Spirometer and attached flow head function together as a pneumatachomater

Pneumotachometer Hot Wire Anemometer Spirometer

Electrical Characteristics

The Pasport PS-2152 Spirometers use the Integrated Silicon Pressure Sensor from the MPXV5004G series.

DATASHEET copy.jpg

The pressure signal is transmitted to the silicon diaphragm inside the sensor. Dry air is used as the pressure media.The output signal relative to the pressure input is as follows:

Pin Descriptions

Pins 1,5,6,7 and 8 are internal device connections and are not connected to external circuitry or ground. Pin 2 is the Input Voltage pin and works at 5.0Vdc and I am supposing that it gets connected to the microprocessor. Pin 3 being ground and Pin 4 being the Output Voltage.

Microcontroller Connections

I have not had the opputunity to hook up the sensor with a pic myself. Here is a how it is connected in the device.

Using the MPXV5004GC7U(absolute pressure sensor) instead of the MPXV5004DP (differential pressure sensor)

[|Datalogging by Sending Raw Values]

Other Links and projects

Similar sensor with two outputs
Thermistor-based Breathing Sensor for Circadian Rhythm Evaluation
Motion Capture
Frequency Content of Breath Pressure and Implications for Use in Control
Breathe Actuated Triggers