hey guys...
can somebody help me how to measured air flow in your lugs like spirometer..what sensor can i use to measured it...please i really tired to see it works.
Try a thermistor fitted to the mouth piece intake. You need a very small one that can sense the temperature difference between inhaled and exhaled air. This idea was used for research to sense the breathing of babies, the thermistor was located at the nasal passage for that. Of course you need a very sensitive amplifier to get a recordable output.
We have pressure differential sensing air flow sensors here at the uni but they are way beyond reach of an individuals budget :wink:
You might try a little fan with a tachometer to detect air flow. Just put the fan in a tube and have the person breathe through the tube. It wouldn't be very accurate but it would be cheap and easy to build.
A thermistor is heated by radiated heat created by a small (very small) coil wrapped around it. When air flows past the coil, it draws heat away from the coil/thermistor, droping the resistance. Using a wheatstone bridge and a second thermistor upstream from the heated thermistor, you may use an op-amp to generate the delta in temp difference.
You might take a look at a rotameter or similar flowmeter. These use a plug or ball inside a tapered tube. The fluid (air in this case) flows from bottom to top and the height of the plug or ball is correlated with flow rate. Dwyer, among others, makes these. The nice thing is that they are relatively inexpensive and are relatively accurate.
You might then adapt some optical or magnetic means to indicate position of the plug or ball - and intergrate the data with a PIC or similar controller. It's possible that the rotameter manufacturer has already provided for this interface.
Along the same lines as the "fan" they do make flow indicators that spin a propellor or wheel that is visible in a sight window. A simple optical counter could be adapted easily - interface with a PIC or similar device then calibrate against a known standard.
In all cases you might want to provide for regular cleaning of the internals as well as provide a low resistance air filter to keep liquids and aerosols from gumming things up.
They do make relatively inexpensive pressure sensors that you could use along with a carefully selected orifice. If you know the pressure on both sides of the orifice you as well as the characteristics of the orifice then you can easily calculate the flow and integrate over time. I saw these sensors for sale at a flea market for $5 this past weekend. Made for automotive use but certainly adaptable.
Note that in all cases resistance to flow or backpressure can affect the flow measurement but more important it can impact the behavior of the lungs. You may want to do some research on the established standards if you plan on comparing data. Above all, don't create something that will hurt someone.